The Astronomist

Sunset

2012-01-10T10:29:00.000-08:00

Proffesor Frédéric Pont at the University of Exeter has simulated what sunsets on planets orbiting distant stars would look like.

What does the sunset look like on HD 189733 b? Amazingly, we know quite accurately. This is because the colour of the sunset is exactly what is measured when collecting the transmission spectrum of the atmosphere of a transiting planet. We have measured the transmission spectrum of ’189 with the STIS spectrograph on the Hubble Space Telescope. STIS covers visible wavelengths, and HD 189733 is bright enough that the precision of the spectrum is sufficient for a precise translation into colours perceived by the human eye.

What does the sunset look like on HD 209458 b?

Temporal Cloak

2012-01-08T19:10:00.000-08:00

The physics and optics blog, Skulls in the Stars, ask this what is a “temporal cloak”, anyway?

I’ve been saying for a few years that optical science has entered a truly remarkable new era: instead of asking the question, “What are the physical limitations on what light can do?”, we are now asking, “How can we make light do whatever we want it to do?” Among other things, we can make light travel “faster than light“, we can focus light through a highly scattering material, we can take high-resolution pictures with low-resolution sensors, and even make particles “fly” on a “wind” of light!

Inevitably, though, many of these discoveries get misinterpreted in popular news accounts to the point that their real significance is lost in a haze of science fictional, or even supernatural, hype. A good example of this is the “picosecond camera” that I described last week, which is an amazing achievement but also possesses a number of technical limitations that make it not quite a “camera” in the ordinary sense of the word.

This week, the experimental realization of a “space-time cloak” or “temporal cloak” by researchers at Cornell University has made national news.

Read on.

Nothing

2012-01-04T17:02:00.000-08:00

Ethan Siegel over at his blog Starts With a Bang has some more interesting ideas on the physics of nothing and everything here and here.

This Year

2012-01-01T22:19:00.000-08:00

The Boundary Between Knowledge and Belief

2011-12-26T13:56:00.000-08:00

The director of CERN, Rolf-Dieter Heuer, talks to European Magazine.

It’s a quest for knowledge. The questions we are examining have been asked since the beginning of mankind. We are humans, we want to understand the world around us. How did things begin? How did the universe develop? That distinguishes us from other creatures. If you go outside at night and look up into the sky, you cannot help but dream. Your fantasy develops, you are naturally drawn to these questions about being and existence. And at the same time, our work has very practical consequences. When antimatter was introduced into the theoretical framework 83 years ago, nobody thought that this had any practical relevance. Yet today, the concept is used in hospitals around the world on a daily basis. Positron Emission Tomography (PET) is based on the positron, which is the anti-particle to the electron. Or take the internet. The idea of a worldwide network started in 1989 here at CERN, because we needed that kind of digital network for our scientific work. That’s the beauty of our research: We gain knowledge but we also gain the potential for technological innovation.

More here.

The First Quantum Computer

2011-12-12T12:10:00.000-08:00

In a nondescript office park outside Vancouver with views of snow capped mountains in the distance is a mirrored business park where very special work is being done. The company is D-Wave, the quantum computing company. D-Wave's mission is to build a computer which will solve humanity's grandest challenges.

D-Wave aims to develop the first quantum computer in the world, perhaps they already have. The advent of quantum computers would be a sea change in the world that would allow for breaking of cryptography, better artificial intelligence, and exponential increases in computing speed for certain applications. The idea for quantum computers has been bubbling since Richard Feynman first proposed that the best way to simulate quantum phenomena would be with quantum systems themselves, but it has been exceedingly difficult to engineer a computer than can manipulate the possibilities of quantum information processing. Hardly a decade ago D-Wave began with a misstep which is the origin of their name. D-Wave got its name from their first idea which would have used yttrium barium copper oxide (YBCO) which is a charcoal looking material with a superconducting temperature above that of the boiling point of liquid nitrogen. This means that YBCO is the standard science lab demonstration of superconducting magnetic levitation. Ultimately the crystalline structure of YBCO was found to be an imperfect material, but the cloverleaf d-wave atomic orbital that lends YBCO its superconducting properties stuck as D-Wave's name. The vision of D-Wave did not change, but their approach did. They realized they would have to engineer and build the majority of the technology necessary to create a quantum computer themselves. They even built built their own superconducting electronics foundry to perform the electron beam lithography and metallic thin film evaporation processes necessary to create the qubit microchips at the heart of their machine.

I recently got to visit D-Wave, the factory of quantum dreams, for myself. The business park that D-Wave is in is so nondescript that we drove right by it at first. I was expecting lasers and other blinking lights, but instead our University of Washington rented van pulled into the wrong parking lot which we narrowly reversed out of. In the van were several other quantum aficionados, students, and professors, mostly from computer science who were curious at what a quantum computer actually looks like. I am going to cut the suspense and tell you now that a quantum computer looks like a really big black refrigerator or maybe a small room. The chip at the heart of the room is cooled to a few milikelvin, colder than interstellar space, and that is where superconducting circuits count electric quantum sheep. The tour began with us milling around a conference room and our guide, a young scientist and engineer, was holding in his hand a wafer which held hundreds of quantum processors. I took a picture and after I left that conference room they did not let me take any more pictures.

Entering the laboratory it suddenly dawned on me that this wasn't just a place for quantum dreams it was real and observable. The entire notion of a quantum computer was more tangible. A quantum computer is a machine which uses quantum properties like entanglement to perform computations on data.The biggest similarity between a quantum computer and a regular computer is that they both perform algorithms to manipulate data. The data, or bits, of a quantum computer are known as qubits. A qubit is not limited to the values of 0 or 1 as in a classical computer but can be in a superposition of these states simultaneously. Sometimes a quantum computer doesn't even give you the same answer to the exact same question. Weird. The best way to conceive of a quantum computing may be to imagine a computation where each possible output of the problem has either positive or negative probability amplitudes (a strange quantum idea there) and when the amplitudes for wrong answers cancel to zero and right answers are reinforced.

The power of quantum computers is nicely understood within the theoretical framework of computational complexity theory. Say for example that I give you the number 4.60941636 × 10¹⁸ and ask for the prime factors of this number. Now if someone were to give you the prime factors you could verify them as correct very quickly, but what if I asked you to generate the prime factors for me (I dare you. I have the answer. I challenge you). The quintessential problem here is the P versus NP question which asks whether if a problem can be verified quickly can it also be solved quickly. Quickly is defined as polynomial time meaning that the algorithm scales as the number of some inputs to some power. Computational complexity theory basically attempts to categorize different kinds of problems depending on how fast a solution can be found as the size of the problem grows. A P class problem is one in which the solution can be found within polynomial time. A NP class problem is one in which the solution can be verified in polynomial time. So if I ask you for the prime factors of my number above that is an NP problem because given the numbers you could verify the answer quickly, but it would be very difficult to calculate the numbers just given the number. It is an open question, but it appears likely that all P problems are a subset of NP. This means that problems verifiable in polynomial time are not necessarily solved in polynomial time. The issue is that for some very interesting problems in the real world we could verify the answer if we stumbled upon it, but we won't even be able stumble upon the answer in a time shorter than the age of the universe with current computers and algorithms. What we know we know and what we think we know is a sea of confusion, but the popular opinion and where people would take their wagers is that P is not equal to NP.

Suddenly, with mystique and spooky actions at a distance, quantum computing comes swooping in and claims to be able to solve some NP problems and all P problems very quickly. A general quantum computer would belong to the complexity class of BQP. There is a grand question at hand, is BQP in NP? (More generally, is BQP contained anywhere in the polynomial hierarchy? The polynomial hierarchy is a complexity class which generalizes P and NP problems to a particular kind of perfect abstract computer with the ability to solve decision problems in a single step. See this paper here on BQP and the Polynomial Hierarchy by Scott Aaronson who is a outspoken critic of D-Wave) At this time we cannot even claim to have evidence that BQP is not part of NP, but most scientists close to the problem think that BQP is not a subset of NP. Quantum computing researchers are trying to get better evidence that quantum computers cannot solve NP-complete problems in polynomial time (if NP was a subset of BQP then the polynomial hierarchy collapses). A reasonable wager I would take is that P is a (proper) subset of BQP and BQP is itself is a (proper) subset of NP. This claim has not been rigorously proved but it is suspected to be true and further there are some NP problems which it has been shown to be true for such as prime factorization and some combinatoric problems.

There might be an elephant in the room here. The D-Wave architecture is almost certainly attacking a NP complete problem and reasonable logic says that quantum computers will solve P problems and some NP problems, but not NP complete problems (this is also not proven, but suspected). An NP complete problem is a problem in which the time it takes to compute the answer may reach into millions or billions of years even for moderately large versions of the problem. Thus we don't know if this particular quantum computer D-Wave has built even allows us to do anything efficiently we couldn't already do on a classical computer efficiently; it doesn't seem to be a BQP class computer thus it cannot for example solve prime factorization cryptography problems. So, yes it is a quantum machine, but we don't have any evidence it is an interesting machine. At the same time we don't have any evidence it is an uninteresting machine. It is not general purpose enough to be clear it a a big deal, nor is it so trivial it is totally uninteresting.

The D-Wave lab was bigger than I expected and it was at once more cluttered and more precise than I thought it would be. It turns out the entire process of quantum computing follows this trend. There are a lot of factors they contend with and on the tour I saw people dead focused with their eyes on a microscope executing precise wiring, coders working in pairs, theoreticians gesturing at a chaotic white board, and even automated processes being carried on by computers with appropriately looking futuristic displays. The engineering problems D-Wave faces include circuit design, fabrication, cryogenics, magnetic shielding and so on. There is too much to discuss here so I will focus on what I think are scientifically the two most interesting parts of the D-Wave quantum computer which are the qubit physics and the quantum algorithm which they implement; in fact these two parts of their computer are deeply intertwined.

In the image above is a wafer of Rainer core superconducting microchips. The chips are built to exacting specifications and placed at the center of the D-Wave quantum computer in isolation from external noise such as magnetic fields and heat. In the quantum world heat is noise so the chips are kept at a temperature of a few milikelvin to preserve the quantum properties of the system. On each chip are 128 superconducting flux qubits. The qubit is the quantum of information with which this computer works. There are various ways with which to create a quibit such as quantum dots, photons, electrons, and so on, but D-Wave has gone with the flux qubit design for engineering conerns.

A flux qubit is a micrometer size loop of conducting material (in this case Niobium) wherein a current either circulates the loop clockwise or counterclockwise in a quantized manner such that the loop is either in a spin up (that is +1 or ↑) or a spin down (that is -1 or ↓) state. There is an energy potential barrier between the loop spontaneous flipping spin (or current circulation direction) which can be modulated through various control schemes. They control these loops using compound Josephson junctions and SQUIDs using their own propriety techniques, but borrowing heavily on decades of advancement in solid state physics.

Perhaps even more important than the qubit itself is the architecture and the algorithm implemented by the computer. They use a quantum adiabatic algorithm based on the Ising model. When I realized that their algorithm was based on the Ising model I couldn't help but marvel at the powerful simplicity. The Ising model is a statistical mechanics model of ferromagnetism where the atoms (vertices or variables) in a metal (crystal lattice or graph) are discrete variables with spin values that take on spin up or spin down values and each spin interacts with its nearest neighbors. It is a simple model that leads to beautiful complexity (for example see this article on the Ising model here) especially when you allow the interaction of each spin with its neighbor to be finely controlled or when you allow the connectivity of the vertices to be varied. The Ising model is easily extended to more abstract problems. For example we can connect every single vertex to every other vertex, it wouldn't look like a crystalline structure any more, but it makes sense on paper or with wires on a chip.

The quantum adiabatic algorithm borrows ideas from physics such as the process of annealing and spin states in the Ising model to solve a generalized optimization problem. During my tour of D-Wave we continued to talk about the algorithm and what was possible and the whole concept slowly crystallized for me, but it is not immediately obvious why they designed the computer they way they did because their implementation would not create a universal quantum computer. Why the quantum adiabatic algorithm?

Quantum annealing is physically motivated method for a quantum computers which is not thwarted by thermodynamics or decoherence.
Real world optimization problems can be modeled using the Ising spin glass. The hardware mirrors this.
More complicated architectures will borrow from the quantum annealing approach such as a universal adiabatic quantum computer.

D-Wave has not created a general purpose quantum computer. They have created a quantum computer which solves the adiabatic quantum algorithm or equivalently an optimization problem. They use quantum annealing to solve the global minimum of a given objective function with the form of... Wait, wait, let me have a kitten tell you instead (math warning next to paragraphs):

Here E is the value to be minimized over the total system state s subject to the constraint of J_ij (where J_ij<1) acting between each element s_iand s_j(where all s=+/-1). Each element s is weighted by the value h_i(where h_i >-1). The nearest neighbor spins of each ij pair is calculated according to the connections between vertices in a physics application or depending on the microchips graph architecture of actual physical connections on the D-Wave chip. ) The coupling between ij is determined by J_ijso this means that J represents your knowledge of how each component of the system interacts with its neighbors. Immediately we extend the above minimization parameterization to the physical implementation of quantum flux qubits.

In this new form the optimization problem is written as a Hamiltonian which determines the interaction and evolution of the system. The variables are modified, s_j→σ_z ⁱ and s_i→σ_z ⁱ where σ_i ^z are are Pauli matrices at site i for a spin 1/2 qubit. Then h_i is the transverse field that represents transitions up and down between the two spin states ↑ and ↓, of each spin. Here K_ij is the weighting that defines the interaction between the qubits. The problem is to anneal the system as closely as possible to its classical ground state with the desired K_ij.

The D-Wave computer solves the the quantum adiabatic algorithm by initializing the spins of the flux qubits in their ground state with a simple Hamiltonian. Initially the potential well for the spin of qubits is U shaped; the ground state of the of the qubits when they are configured in this mode is a superposition of the |↑> and and |↓> flux basis. Then the qubits are adiabatically, or slowly, evolved to the specific Hamiltonian which encodes the optimization problem that is to be solved; the potential is evolved to the double-welled configuration at which point the ↑> and and |↓> states start to become the dominant basis. Actually, the final configuration is not exactly a double-welled symmetric state, but it has some relative energy difference between the to states which biases the machine towards the encoded problem. Evolving the Hamiltonian can be thought of as modifying the energy barrier between the spin up and down states for each flux qubit. In a real system each potential well has multiple energy levels possible in it besides the lowest energy state which is where the ideal calculation is performed. According to the adiabatic theorem the system remains in the ground state so that at the end the state of the system describes the solution to the problem. However, in a real machine noise, such as the ambient local heat, can still disturb the system out of the ground state. A key advantage to the D-Wave approach is robustness to noise in many situations. The slower the Hamiltonian is evolved, the more the process adheres to the ideal adiabatic theoretical calculation. Performing the calculation more slowly decreases the chance of jumping out of the ground state. Adding more qubits makes the energy gap at the tipping point smaller. Thus engineering is a machine with more qubits is hard. Interestingly, because quantum machines have statistical uncertainties each computation will have uncertainties which can be reduced by either running each calculation slower (and we are talking a few microseconds here) or by running the same calculation many times and seeing what different answers come up. As it turns out it is usually faster to run the calculation many times and compare answers than run one long calculation.

The theoretical minimization problem that is solved is best understood separately from what the actual quantum qubits are doing. Over at the D-Wave blog, Hacking the Mulitiverse, they liken the optimization problem to finding the best setting for a bunch of light switches that have various weightings. Each light switch can be either on or off and can have an either positive or negative weighting, the h_iterm above, and it can have a dependency on any other switch in the system determined by the J_ijterm. It turns out to a be a really hard problem as for just 100 switches there would be 2¹⁰⁰ possible ways to arrange the switches.

Traditionally the first program a coder writes in a new language is a simple print statement which says Hello world. On a quantum computer the first program you write says Hello multiverse! You could write this program on a D-Wave. Yes, you really can because you can go out any buy one. Lockheed Martin bought one earlier this year for ten million dollars. The detractors to D-Wave would say you are not getting a real quantum computer, but then why did Lockheed Martin buy one? It is legitimate to ask, is D-Wave if the first true quantum computer? This of course depends on your definition of a quantum computer. The answer is probably no if you want a universal quantum computer (which belonged to the BQP complexity class discussed earlier). Probably no here means that reasonable computer scientists studying quantum computers have excellent reason to believe the answer is no but they lack rigorous mathematical proof. On the other hand if you are looking for a computer which exploits quantum effects to implement a specific purpose quantum algorithm then I think you can safely say, yes, this is a quantum computer. I am just a naive astronomer though so don't take my word for it. So let me clarify and say that just because a computer exploits quantum mechanics does not make it a quantum computer. All microchips today are small enough that the designers know something about quantum mechanics, maybe they even have to account for it in the chip's design, but crucially the compilers and the code that is written for the machine has no knowledge of the quantum mechanics. The algorithms run on the machine assume nothing about quantum mechanics in our universe. However, a real quantum computer would obviously be programmed according to the rules of quantum mechanics. Indeed the the D-Wave computer is executing an algorithm which explicitly takes into account quantum mechanics. Further, whether or not the D-Wave computer is actually a quantum computer that will satisfy computer scientists definition is a mute point compared to asking if it is useful. Currently D-Wave is running experiments that show that the speed scaling of their machine as a function of inputs is, hopefully, better than classical computers and algorithms. In the future they will have to show with double blind experiments that their machine scales better than classical machines. If they can execute calculations in a few microseconds which take classic computers decades I don't care if you call it the one true quantum computer or an oracle, I will just want one.

References

Harris, R., Johansson, J., Berkley, A., Johnson, M., Lanting, T., Han, S., Bunyk, P., Ladizinsky, E., Oh, T., Perminov, I., Tolkacheva, E., Uchaikin, S., Chapple, E., Enderud, C., Rich, C., Thom, M., Wang, J., Wilson, B., & Rose, G. (2010). Experimental demonstration of a robust and scalable flux qubit Physical Review B, 81 (13) DOI: 10.1103/PhysRevB.81.134510

Harris, R., Johnson, M., Han, S., Berkley, A., Johansson, J., Bunyk, P., Ladizinsky, E., Govorkov, S., Thom, M., Uchaikin, S., Bumble, B., Fung, A., Kaul, A., Kleinsasser, A., Amin, M., & Averin, D. (2008). Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling Physical Review Letters, 101 (11) DOI: 10.1103/PhysRevLett.101.117003

Superluminal claims require super evidence

2011-09-26T19:30:00.000-07:00

Neutrinos, those mercurial smidgens of the particle world, travel faster than the speed of light. That's the claim the OPERA collaboration makes in a paper subtly titled: Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. This is a big claim that could have implications for particle physics and time travel. It has made the news, news, news, news, but what does it all mean? Lets talk about neutrinos.

First, let me say that if neutrinos do travel faster than the speed of light then physicists have a lot of explaining to do. The repercussions of faster that light travel for any particle (also known as superluminal travel) would be revolutionary. So revolutionary that most physicists I spoke to this past week at a conference did not take the news too seriously: it was too extraordinary to comment on without further thought and details. The OPERA collaboration is actually very brave for putting this paper out there (i.e. on the ArXiV) and asking for outside analysis. They don't even pretend to begin to consider the ramifications. The last line of the paper sums up their position:

We deliberately do not attempt any theoretical or phenomenological interpretation of the results.

So let me ignore the wild theoretical implications and discussions of tachyons and just talk about the experiment and an astrophysical constraint on the velocity of neutrinos.

Why are physicists so confident that neutrinos travel at the speed of light? Well, start with the fact that every piece of credible data ever taken has never seen anything—be it particle or information—travel faster than the speed of light. Given previous observations it is hard to understand how neutrinos could be any different. Of course neutrinos are very difficult to measure because they interact very weakly with regular matter. Consider that 60 billion neutrinos generated from the core of the sun pass through your pinky each second and none of them interact with you (nor do they interact with the Earth, they are passing through you day and night).

The creation and detection of neutrinos is complicated. The process begins for the OPERA experiment over at CERN where the Super Proton Synchrotron (SPS) creates high energy (400 GeV/c) protons that collide with a graphite target producing pions and kaons which decay into muons and muon neutrinos. The neutrinos coming out of SPS are almost pure muon type neutrinos with an average energy of 17 GeV. The neutrinos travel through the solid Earth in a straight path unimpeded into a cavern below a mountain, Gran Sasso, in Italy. The OPERA neutrino experiment was designed to look for the direct appearance of muon to tau neutrinos (ν_μ → ν_τ), but their anomalous findings on the velocity of neutrinos is much more interesting.

The OPERA experiment found that the velocity of neutrinos was about 0.00248% faster than the speed of light. This measurement was made by precisely measuring the distance traveled by neutrinos and the time of travel. The OPERA collaboration did a lot of work to measure both parameters precisely. They found this velocity by measuring that the time of arrival of neutrinos at their detector by using atomic clocks. Their measurement was precise to a few nanoseconds. Wow, that is quick. Light only travels about a foot in a single nanosecond.

In order to measure the distance between CERN and Gran Sasso the OPERA team used very precise GPS systems. For example, they noticed a 2009 earthquake in that area produced a sudden displacement of 7 centimeters. So the exact distance the neutrinos traveled was 730534.61±.20 meters (or about 2.44 light milliseconds), however some have suggested that the GPS based positioning they used has errors introduced by atmospheric refraction. Intriguing possibility.

In order to measure the time, what OPERA calls the time of flight measurement, they used atomic cesium clocks. But the 'time' cannot be precisely measured at the single interaction level since the protons from the SPS source have a 10.5 microsecond extraction window. They had to look at time distributions where the most likely time for a burst of neutrinos to be created was inferred to higher precision. Additionally, the actual moment where the meson produces a neutrino in the decay tunnel is unknown, but it introduces negligible inaccuracy in the time of flight measurement. So, these distance and time measurements are really important, but really subtle. I recommend reading the paper if you are a glutton for punishment.

There is a very interesting constraint on the speed of neutrinos that comes from astronomy. It was the neutrinos and photons released from the death of a star. Supernova 1987A (SN 1987A) exploded 168,000 years ago when fusion in the core of an old star ceased and the weight of the outer layers of the stars caused the core to collapse. The protons in the atoms of the core of the star merged with the electrons present and converted themselves into neutrinos and electron neutrinos. A mega amount of electron neutrinos, about 10⁵⁸, were generated and they began their epic journey to Earth. Some of these neutrinos arrived on Earth one morning in February of 1987 in a burst lasting less than 13 seconds. Of those many neutrinos two dozen interacted with detectors on Earth.

Astronomers observed light from SN 1987A just three hours after the neutrinos arrived. Just such a delay is expected as the fireball of the supernova had to have some time to expand and become transparent to photons, whereas neutrinos could escape much sooner. The explosion occurred at a known distant out in the Large Magellenic Cloud. This distant explosion created photons and neutrinos in a timed race to the Earth. With the these measurements in hand (the distance to the supernova and the time of arrival of the photons compared to neutrinos) we can determine the speed of neutrinos from SN1987A.

The accuracy and precision of measurements from SN 1987A are actually much greater than measurements taken at Gran Sasso despite the three hour time window difference between neutrino and photon travel. It comes down to the fact that the relative distance between Earth and SN 1987A is about 10¹⁶ times larger than the distance between CERN and Gran Sasso. This means that time measurements from SN 1987A can be extremely imprecise and still be much more precise than the OPERA measurements.

If the neutrinos from supernova 1987A had been traveling as fast as the neutrinos detected at Gran Sasso they would have arrived about four years sooner than the light from SN 1987A.

This supernova constraint on the velocity of neutrinos is very nice, but it doesn't answer every question because the comparison may not be apples to apples. The OPERA neutrinos are tau type, not electron type. And they are traveling through the Earth, not empty space. And they were much higher energy. The neutrinos from SN 1987A were only about 10 MeV, about one hundred times lower energy than the neutrinos in this study. Some may argue that higher energy neutrinos travel faster than lower energy neutrinos. However, a velocity-energy dependence should have stretched out the 13 second arrival time of neutrinos. Further, part of the OPERA collaborations analysis involved splitting the data into two bins with mean energies of 13.9 and 42.9 GeV; a comparison between the two bins indicated no energy dependence on velocity. Thus, while it may still be true that GeV neutrinos move faster than MeV neutrinos, the theoretical wiggle room is shrinking.

This experiment may be a signal of new physics or a case of systematic errors. Yet, even physicists who have developed theories that allow for superluminal velocities are doubtful so I would not bet on proof of hidden extra dimensions or time travel to come from this experiment. Much more extraordinary evidence is necessary to confirm such an extraordinary claim as breaking the speed limit of our Universe.

Turtles all the way down

2011-09-08T20:45:00.000-07:00

The beginning was heralded by an elephant's trumpet.

The universe is carried on the back of an ancient turtle.

There were once ten suns embodied by crows. All but one crow was shot by an archer.

The moon is a decapitated head. Her face is painted with bells.

The stars are your ancestors eyes worth remembering.

In time you too will have nine tails and be older and wiser.

All the things which you do not know are vague. Drift clouds.

Having come so far is a matter of vagueness.

I wrote this poem because even modern cosmology faces infinite regression paradoxes with respect to the initial impetus of the Universe. The various creation stories independently formed in different cultures create some stunning mental images for me. The funniest idea for me is that the Universe is resting on the back of a giant turtle. What is the turtle resting on? Why it is turtles all the way down. Oh, and I almost forgot the best blog posts always have a picture; here is a picture of a turtle.

You've been Westinghoused Mr. Edison

2011-08-25T13:58:00.000-07:00

Recently while glancing through an old physics text I found a line I had underlined, Westinghouse Electirc Corporation, and I remembered a little phrase that I used to use with other physics students. The phrase was, you've been Westinghoused. Let me explain. There is a curious episode in history know as the the war of the currents wherein the early pioneers of electricity were trying to commercialize the transmission of electricity. Nikola Tesla with the financing of George Westinghouse supported alternating current (AC) against Thomas Edison who supported direct current (DC). Edison tried to discredit the idea of AC transmission by showing how dangerous it was. Edison attempted shenanigans like electrocuting an elephant in public, but in the end practicality and economics prevailed. AC transmission is much more viable than DC transmission because of the pure physics: with DC transmission in order to get adequate power transmitted either the wires would have to be copper as thick as your arm or you would have to have power stations every block or so. It was probably a combination of physics and the shrewd business sense of Westinghouse that it came to pass that Edison lost the war of the currents. This history, like the story of Bohr and Heisenberg, has interesting characters and a certain mystique that lends itself to historical plays and documentaries.

Tesla was a modern Prometheus. Some say that history overlooked Tesla, however, there is a current (pun intended) revival in interest for Nikola Tesla, if not always for his science, for his eccentric personality. This documentary about Tesla talks about his life and work. The part about the war of the currents begins at 18:35.

Now, as Edison fought against AC current he tried to be really clever and he wanted to brand death by electrocution as being Westinghoused. However, Edison's electric empire faded and history summarily shows that he was bested by Tesla and Westinghouse. Scientists are a competitive bunch, so I propose that when one colleague bests another colleague in an academic pursuit, we proclaim that the the defeated has been Westinghoused. It isn't the worst thing to be Westinghoused, it just means you were bested in that pursuit. Edison was a great inventor and is still famous to this day, but he surely got Westinghoused.

Sailing

2011-08-19T16:28:00.000-07:00

There was an amazing article up on Wired today about the America's Cup. It reminded of just how cool competitive sailing is. I wrote about sailing upwind in 2009 before the last America's Cup race and I mentioned a revolutionary solid wing multihull boat created by team Oracle. That boat was in fact as fast as promised and it won the race and by doing so team Oracle won the right to dictate the rules of the next America's cup. What they did was create the America's Cup World Series of standarized fixed wing catamaran sailing boats (you can read more about the entire thing in the Wired article). These boats are super fast and super intense. The America's Cup World Series is the water equivalent of Formula 1, but instead of crashes there are capsizes. Well, actually there are crashes too. Here is a hectic highlight real of these boats racing in the first ever event a few days ago in Cascais, Portugal.

Modern sailing is a paradoxical mix of elements. The boats are designed with advanced knowledge of physics and constructed of carbon fiber, yet they are powered by the simplicity of the wind. I think there is an appeal to working with nature to accomplish work rather than fighting against it. Working with nature always seems to be the most graceful option. In space travel rather than firing rockets to propel ships it is advantages to use gravitational assists by swinging by planets. And then of course there are solar sails in space too. The Japanese IKAROS satellite recently successfully unfurled itself in space and is now being pushed by photons on a unique journey. If you think about it astronomy and sailing go together.

A Cubic Millimeter of Your Brain

2011-07-27T01:15:00.000-07:00

Are there more connections in a cubic millimeter of your brain than there are stars in the Milky Way? We are going to answer that question in a moment, but first take a look at this image of hippocampal neurons in a mouse's brain. It is an actual color image from a transgenic mouse in which fluorescent protein variations are expressed quasi-randomly in different neurons. This kind of image is known as a brainbow and is aesthetically awesome further it may be one way to empirically examine a cubic millimeter of the brain (neuron tomography).

In reality mapping even an entire cubic millimeter of the brain is an extremely daunting task, but we can still answer my original question. First, I know that there are different kinds of neurons that vary in size and that some neurons can have a soma (the big part that has the nucleus from which the dendrites extend) spanning a millimeter in size. Thus if you picked a random cubic millimeter of brain you could run right into the heart of a neuron and you would find very few connections. Given this fact, we can very easily answer this question with a resounding no, however, this seems like an unsatisfactory trite approach. So I looked up some numbers on how many neurons are in the brain, how many connections are in the brain, and how many stars are in the Milky Way. Lets answer the question using the 'average' number of connections per cubic millimeter.

How many neurons and connections there are in the brain? This is kind of a tricky question and I am not a nuerobiologist so I have gone to several resources for the answer. Professor of Computational Neuroscience at MIT Sebastung Seung says in a TED talk

your brain contains 100 billion neurons and 10,000 times as many connections

Professor of Molecular Cellular Physiology at Stanford Stephen Smith says in a press release on brain imaging that

In a human, there are more than 125 trillion synapses just in the cerebral cortex alone

René Marois from the Center for Integrative and Cognitive Neurosciences at Vanderbilt Vision Research Center states in a recent paper ^[1]

The human brain is heralded for its staggering complexity and processing capacity: its hundred billion neurons and several hundred trillion synaptic connections can process and exchange prodigious amounts of information over a distributed neural network in the matter of milliseconds.

I have enough expert sources now to confidently say these experiments agree that the human brain has some 100 billion neurons (10¹¹). The number of connections seems less precise, but it is at least several 100 trillion connections (10¹⁴) as judged by Marios and Smith and as much as 10¹⁵ as judged by Seung.

The number of connections in the brain is tricky to define. We may define a synaptic connection as each place the neuron touches another neuron and a synapse is present. It doesn't seem to make sense to simply count incidental contact. Further, there is the question of whether we should count redundant contacts between neurons. We can obtain an upper bound on the number of connections in the brain by considering the case in which every neuron is connected to every other neuron. Coincidentally the operation of connecting every node in a network with every other node is a process I am familiar with from cross correlating radio signals. Anyways, the equation we are looking for is N(N-1)/2 where N is the number of nodes in the network. Thus, for our N=10¹¹ neurons the maximum number of non-redundant connections is about 10²². This maximum bound is huge! But how huge is it really? Hilariously, while searching for an answer to my original question I found a message board pondering the grand statement

There are more connections in the brain than atoms in the Universe.

A really clever person pointed out that

Theoretically, if we took all the atoms in the universe; wouldn't that include the atoms within the brain?

People have this feeling that the number of connections between items can be much larger than the number of actual items in the collection and while this intuition is true the idea that there are more connections in the brain than there are atoms in the universe is absurd. Lets put it in perspective that a few grams of any substance, like water, is measured units of moles. A mole is standard unit of measurement corresponding to the absolute 6.02 x 10²³. Thus even a drop of water contains more atoms than there are connections in the brain.

Now we need to know how many neurons and connections are in an average cubic millimeter of the brain. How big is the brain? John S. Allen of the Department of Neurology at University of Iowa stated in a recent paper that^[2]

The mean total brain volumes found here (1,273.6 cc for men, and 1,131.1 cc for women) are very comparable to the results from other high-resolution MRI-volumetric studies.

We can take the volume of the brain as 1000cc as a low estimate (which will only over estimate the density of connections).

The final thing we need to know to answer the question at hand is the number of stars in the Milky Way. Like every other number we have been working with it is rather uncertain. Even if we define a star as only those spheres of gas which are large enough to fuse hydrogen at some point in their lifetime we don't know the answer because we can't see the multitudes of dim stars. There are probably at least 500 billion star like objects in the Milky Way. Lets take 100 billion as the number to be conservative.

Finally, lets bring all the numbers together. One cubic millimeter is 1/1000 of a cubic centimeter and 1/1000000 (10^-6) of the entire volume of the brain. We can scale the total number of connections in the brain (using the high estimate of 10¹⁵ connections in the brain) then we find that there are 10⁹ connections in a cubic millimeter of the brain. The 10⁹ connections in a cubic millimeter of the brain is two orders of magnitude smaller than a low estimate of the number of stars in the Milky Way. No, on average there are not more connections in a cubic millimeter of your brain than there are stars in the Milky Way.

My first response to this question was bullshit! This question (or rather statement) is made by David Eagleman here at a TEDx talk and here on the Colbert Report. Colbert also called out Eagleman when he dropped this factoid, but it didn't stop the interview. I have also contacted some actual neuroscientists to see what they thought of this statement and they agree with me that it is not true. Maybe there is special part of the brain particularly more dense in connections than the brain on average, but that would be misleading like saying the density of the Milky Way is that of water because, you know, certain parts of the Milky Way are water. The better statement would be to say that there are are more connections in the brain than there are stars in the Milky Way. As Colbert would say, I am putting you on notice Eagleman.

While we are on the subject I want to mention my favorite talk about the brain which mixes just the right amount of wonder and fact. It is the TED talk I mentioned earlier by Sebastian Seung on what he calls the connectome - the network of connections in your brain between neurons which physically dictates how you think. In the video he discusses another volume tomography technique in the brain using a cube of mouse brain tissue just 6 microns on a side. It is another great visualization for what is actually in a cubic millimeter of your brain.

References

[1] Marois, R., & Ivanoff, J. (2005). Capacity limits of information processing in the brain Trends in Cognitive Sciences, 9 (6), 296-305 DOI: 10.1016/j.tics.2005.04.010

[2] Allen, J., Damasio, H., & Grabowski, T. (2002). Normal neuroanatomical variation in the human brain: An MRI-volumetric study American Journal of Physical Anthropology, 118 (4), 341-358 DOI: 10.1002/ajpa.10092

On Replications

2011-07-14T15:14:00.000-07:00

Repetition is ubiquitous and has many different meanings in education, art, literature, science, and life Ideas replicate and mutate; cultural memes spread through culture seamlessly. Manufactured goods are produced as nearly identical as possible. Deviations from the mold are discarded and parts are interchangeable. Digital data is almost limitlessly replicable. Any data or idea committed to the digital world is perfectly copied (sparing the occurrence of a flipped bit) until it is intentionally modified. This characteristic of digital ideas presents a unique challenge for creators of content, distributors, and bored people on the internet. And of course animals and plants on Earth have the ability to self replicate themselves with minor variations. What do we make of all of this?

I am keen on the intersection of art and science on this matter. I like making collages and have highlighted repeated images before with 35 images of space helmet reflections and 100 images of macchiatos. Through repetition and distortion images may be amplified or diminished. It depends on perspective. Generally in artistic endeavors, as in life, the slight variations of a repeated theme are aesthetically pleasing. On the other hand technical work such as engineering, data analysis, or manufacturing requires precise replication. I work in radio astronomy where each radio telescope in the array is nearly identical and the need for precision trumps all other considerations. I find that randomness is never particularly interesting, but neither is absolute order. Somewhere in between these extremes we have something really beautiful.

Looking back and looking forward

2011-07-08T13:55:00.000-07:00

This photo was taken on the last US manned space flight in 1975 before the first shuttle launch in 1981. Portrayed is the historic handshake between Tom Stafford and Alexey Leonov through the open hatch between the American Apollo and Russian Soyuz ships. Today the Atlantis shuttle lifted off for the the last shuttle mission. It is the end of an era. Alas, all good things must end.

Mars Rover Curiosity

2011-07-06T18:01:00.000-07:00

This animation depicts what will happen in August 2012 if all goes as planned for Curiosity, NASA's next Mars rover. This rover is much larger and and more competent than the previous rovers. It is about the size of a small car and has an entire suite of experiments on board. During entry it uses a series of thrusters to maneuver to the designated landing area. Once the ship has slowed down to Mach two (keep in mind that the atmospheric pressure on the surface of Mar's is of the order .05% that of Earth's) a parachute is deployed. As the vehicle slows the heat shield comes off and a radar detects how close the surface is approaching in order to slow for a smooth landing. The last daring step is a so called 'sky crane' which lowers the rover with a long cable from the rocket thrusted ship above. Eventually Curiosity will begin roving, but it won't be limited to roving only during the day by solar panels as the previous rovers were. The large tilted box on the back of the rover contains 4.8 kg of plutonium dioxide which emits heat serving as the power source of the rover. The power should keep flowing for much longer than the minimum specked science mission of two Earth years. The rover will seek out rough rocks such as ancient Martian riverbeds or canyons where evidence of early environments on Mars can be found. The ability to navigate to these areas is an important science requirement for the rover and is one of the reasons for the rover's large size and nuclear battery which should allow it to travel at least 20 kilometers during its lifetime. Geologists and astrobiologists also want to know if certain conditions such as those necessary for organic molecules are present. In the video a laser and a drill are shown performing experiments. The laser is ChemCam which will project onto hard to reach rocks and detect the reflected light in order to discern the chemical composition of rocks. The drill is about a centimeter in diameter and will extract the dust from the holes it creates to run experiments in mineralogy (the laser device inside the rover shown in the video) or detecting organic molecules. All of these experiments aim to answer the question, could Mars have had an environment capable of supporting life at one time?

If the sky crane works we may soon know the answer to this question. Curiosity has a launch window from November 25 to December 18, 2011 from Kennedy Space Center in Florida. And in other news NASA's James Webb Space Telescope is being threatened with the axe in budget bill in the U.S. House of Representatives today. NASA will never run out of adversaries pulling it down: Gravity and the budget.

Gödel's Proof

2011-06-24T16:35:00.000-07:00

There is an idea of reason in the Universe. It is an abstraction which mathematicians have never been content with. Given that scientists exclusively use logic (or mathematical reasoning) for theories and experiments it is of incredible importance to know the limits of logic. It turns out that the study of math itself, metamathematics, has amazing insights on what is knowable.

In 1931 an unassuming paper was published in a German mathematics journal, the title of the paper (translated to English) was 'On Formally Undecidable Propositions of Principia Mathematica and Related Systems I'. It is a confusing title and the kind of paper which I would not understand. The author was a 26 year old Austrian named Kurt Gödel and he had just created a revolutionary idea, but as with so many great ideas it was not simple and it took great minds to fully appreciate it.

The ideas he put forth have been extremely influential and the collective name for the theories that grew from it are known as Gödel's incompleteness theorem. This theorem is a revolutionary outcome in mathematical logical that has implications for not only the philosophy of mathematics, but philosophy in general. It is thus surprising how relatively unknown the theorem is to the general public and even many scientists. I recently read the book Gödel's Proof by Nagel and Newman in just a few sittings at a coffee shop. It is a short and concise explanation of the proof that incrementally brought me closer to understanding the intricacies of Gödel's works.

Gödel's incompleteness theorem is a massive mountain of ideas that I will not attempt to conquer, but I think it is important that everyone at least gets a view. Gödel basically found that no solid guarantee is possible that mathematics is entirely free of internal contradiction. However, Gödel was not out to trash mathematics, contrarily he used mathematics itself to temper the reach of mathematics and place constraints on what is possible to known through mathematics much like a physicist theorizing that a black hole's event horizon places a limit on spaces which the physicist could actually go and measure. Gödel created a new technique of analysis and introduced new probes for logical and mathematical investigation.

The specifics of Gödel's proof even as outlined on wikipedia are extremely complicated (the entire proof is long and there are on the order of 200 links in the article so by the time you were done reading all of the prerequisite mathematical definitions you would have read thousands of pages) for anyone without (or with) extensive mathematical training, so I must admit that I don't understand it completely and not have I attempted to read the actual paper. I want to present here the shortest definition of Gödel's theorem not the the most rigorous.

The key to Gödel's incompleteness theorem is a concept of mapping. In the information age the concept of mapping or coding is familiar to many as in the case of mapping Morse code dots to letter characters. In the explanation that follows take it as a given that it can be shown that all logic systems are equivalent to or mappable to the operators we will be using; this assumption is vital, and I can't quite explain it without detail so I refer the inquisitive mind to read Nagel and Newman's book.

Let us construct a simple logic system using the arbitrary operators P, N, ⊃, and x that have certain properties which we take as given by the table defined below. In the left column a combination of operators is given and in the right column a definition in English of the operators meaning is given.

P⊃x	'print x'
NP⊃x	'never print x'
PP ⊃x	'print xx'
NPP⊃x	'never print xx'

We can combine these statements and create more complicated statements. For example P⊃y where y=P⊃x would mean 'print P⊃x' (note that implicitly I am also using the equals operator). Crucially then NPP⊃x would mean 'never print xx', and this statement could also be written NP⊃xx.

Next ponder what the last statement used on itself means. The statement NPP⊃y where y=NPP⊃ would mean 'never print NPP⊃NPP⊃', but this strange statement could also be written NPP⊃NPP⊃.

So either our system prints NPP⊃NPP⊃ or it never prints NPP⊃NPP⊃. It must do one or the other. If our system prints NPP⊃NPP⊃ then it has printed a false statement because the statement contradicts itself by self reference once it is printed. On the other hand if the system never prints NPP⊃NPP⊃ then we know that there is at least one true statement our system never prints.

So either there are logic statements which may be printed which are false statements, or there are true statements which are never printed. Our system must print some false statements if it is to print all true statements. Or our system will print only true statements, but it will fail to print some true statements.

In the example above I have taken arguments very similar to that in Raymond Smullyan's book Gödels Incompleteness Theorems in order to create an extremely concise, but hopefully accurate description of what lies at the core of Gödel's insight. In Nagel and Newman's book they explain Gödel's proof in much more detail by working out the details of mapping. For example in the explanation above I mapped mathematical statements to the idea of printing, but print could be equivalently be existence. Further, Nagel and Newman argue as Gödel did that all formal axiometric systems can be mapped in some way such that even the most complicated mathematical systems using the common operators of +,-,=, x,0,(,),⊃ and so on can be shown to be incomplete.

Gödel's incompleteness theorem has many forms and implications. Briefly I will demonstrate an analogous, but weaker form of Gödel's incompleteness theorem by analogy to the halting problem. I believe this demonstration is of importance to those of us immersed in the information age and perhaps easier to grasp or at least more applicable than Gödel's work.

The halting problem is to decide whether given a computer program and some input, whether the program will ever stop or will it continue computing infinitely. The key to the halting problem is the concept of computation and algorithms. In the original proof by the enduring Alan Turing specific meanings to the concepts of algorithm and computation were defined. He used a computational machine now known as a Turing complete computer, or a Turing machine. The definition of what constitutes a computer is to the halting problem what the mapping of symbols is to Gödel's theorem. It is at the heart of the problem, and thus actually one of the harder points to define so I will again leave that task as an exercise to the reader.

So lets look at two psuedocode programs and lets imagine that we also have a very special program written by a genius scientist which is called Halting. The scientist claims that Halting can correctly tell your own code B(P,i) whether a program halts.


Program B(P,i) 
  if Halting(P,i)==true then
    return true // the program halts
  else
    return false // the program does not halt

Now here is the important part. The genius scientist claims we can analyze any kind of computer program, this is indeed the crux of the halting program, we want to know if any and every program stops. Now imagine a program E that takes X, which is any program, as an argument.


Program E(X)
  if B(X,X)==true then
    while(true) //loops forever
  else
   return true

The first thing E does is take B and passes it X for both arguments. Program E will get back from B either true or false. If it receives back true it will enter an infinite loop and if it receives back false it will terminate.

So suppose I take B and feed it E for both arguments. What answer will B(E,E) give? Think about it.

We will be running our special Halting program on E(E) which will then run the program B(E,E). The answer to B(E,E) will either be either true or false. If the result is false the program E actually returns true and halts immediately; if the result is true then Halting thinks our program does halt, but the program E throws itself into a loop upon this condition and will never halt. Either way program E lies. E was written very craftily to break B on purpose, but nonetheless the damage is done. E cannot be made reliable even in principle. It matters not how clever you are and or how powerful your computer is. There is simply no reliable computer program that can determine whether another program halts on an arbitrary input. The incompleteness problem may have seemed a little bit distant and philosophical, but if you have read this far it should be evident that the halting problem has deep implications computing.

What does Gödel's theorem mean for the real word, experimental verification, and deductive sciences? Well take for example the Banach-Tarski paradox which states that a solid ball in three dimensional space can be split into a finite number of non-overlapping pieces, and then be put back together in a different way to yield two identical copies of the original ball. This process violates sensible physic notions of conservation of volume and area. It turns out that Banach and Tarski came to this conclusion based upon deductions from the Axiom of choice. Now, whether we know anything at all about the axiom of choice we do know that the deductive conclusions drawn from it are in violation of physics. Thus, a physicist could argue that the axiom of choice is not a valid axiom for our Universe. Within mathematics it is unknown, unprovable Gödel says, whether or not we should accept the axiom of choice, because it is after all an axiom. The argument for whether a given axiom is to be accepted must be discussed outside the confines of the logic structure one is arguing about. It turns out that the axiom of choice is important for many other really important mathematical proofs which are used in physics all the time. I don't know what to make of it really, perhaps a mathematician out their should weigh in on this question.

Another important theorem that goes along with Gödel's theorem is Tarski's undefinability theorem. Tarski's undefinabtliy theorem makes a more direct assertion about language and self referential systems. Basically any language sufficiently powerful to be expressively satisfying is limited. In summation we have two vital points to the concept of incompleteness.

If a system is consistent, it cannot be complete and is limited.
The consistency of the assumptions or axioms cannot be proven entirely within the system.

The repercussions of the meta analysis of logic are profound and subtle. Gödel really has thrown us for a loop. It is unclear if we should draw the line and say this is just a mere curiosity of mathematics or a deep truth about the Universe. It has been proposed by Douglas Hofstadter (author of Gödel, Escher, Bach) that consciousness itself comes from a kind of 'strange loop' induced by a self referential system in our minds. Primarily, I think we can conclude that Gödel's incompleteness theorem implies that in most situations the tools science has to analyze the world are more than adequate because the situations are not self referential. However, I do see a limit to what we can know about the Universe. As physicists forge forward, generally quite successfully, in understanding the Universe it appears that there really is some consistent mathematical basis for our Universe. Many physicists are searching for this mathematical basis to the Universe, it is the so called theory of everything. But does Gödel's result imply that this mathematical basis cannot be self consistent?

Consider this scenario. One day our most powerful, successful, and comprehensive theory ever will predict something that experiment cannot verify or worse an experiment will patently disagree with. Some will argue that the theory must be thrown out because classically the scientific method states that a theory disagreeing with experiment, or making nonsense predictions, is untenable. Another theory will be introduced that makes consistent and testable predictions, however this theory is not able to predict the most intricate traces of nature. Actually, that first case kind of sounds like string theory. Perhaps we will have to start talking about theories being incomplete instead of wrong one day.

G34.3

2011-06-19T15:29:00.000-07:00

Wow, there really is something new to learn everyday.

I Hate Astrology

2011-06-12T19:06:00.000-07:00

Perhaps it is cruel to snuff out the shinning gleam in the eyes of a person who upon hearing that I am an astronomer exclaims, "Oh, I love astrology!" and I reply, "No, I study ASTRONOMY." But they don't understand it. The subtle differences in syllables of the words belies the vast gulf in empirical tendencies between the separate endeavors and it is too much to explain. I simply walk away.

I hate astrology and I hate when people get astronomy and astrology mixed up. I could be more understanding, but I have to choose my battles. I meet a lot of interesting people in coffee shops, bars, airplanes, parties and wherever else life takes me and when someone gets excited about the fact that I study astronomy it means they have a deep curiosity about the skies above. That curiosity is occasionally deeply misguided with astrology and their questions are so fundamentally misconceived I struggle to answer them with candor and accuracy (for example they ask, 'Do the planets affect our daily lives?' and I hesitate to answer honestly that we must consider their gravitational pull, so the answer must be yes). On the other hand I meet people who are genuinely interested in massive collections of gravitationally bound glowing gas and I am very happy to answer their questions.

There is a real danger when logic, or pseudologic, is applied to astrology. Recently there was an uproar about the shifting of the zodiac that made it into some news headlines. Briefly I shared the frustrated sentiments of astrologers because the shifted zodiac has been well known for some time, why is the public just now hearing about it? The book in the image above is from the seventies and claims right there on the cover that, 'Most astrology is unscientific and inaccurate', and goes on to explain the shifted zodiac and how to have a movie ending romance. The ideas in this book are the apotheosis of dangerous thought. A little bit of knowledge is a very dangerous thing when combined with pseudologic in the guise of rigorous proof. It has also not escaped my observation that many of the people I have known who believe in astrology also believe in God as if to demonstrate the utter confusion and inconsistency of their minds. I don't mean to badger defenseless people here. This is simply an honest expression of how I feel. I have summed up my sentiments into a paragraph which I think would be nice to place on a card with which to hand out to people who confuse astrology with astronomy:

I cannot rightly conceive of a logic which would allow one to study such disparate phenomena of love, planets, stars and come to see any connection. Perhaps, desperate for meaning people find it wherever they look; conclusions are forged before the data has been taken. Those who would apply science to astrology may as well attempt to apply science on whom to love and sociologists do study what makes a lasting relationship and neurobiologists study what chemicals are active in the brain during feelings of love, but no scientist will claim that Romeo shouldn't love Juliet. I believe science and an understanding of natural phenomena adds to the beauty life, but pseudologic and lies even when propagated with good intentions ultimately lead to pain and suffering. The human mind has the ability to find patterns anywhere, indeed often where they do not exist.

Making sense of a visible quantum object

2011-06-07T10:56:00.000-07:00

Quantum mechanics predicts that nature is fundamentally uncertain. Particles are in multiple states at once; particles are here and there. As we extrapolate these properties of nature to macroscopic objects the results are counterintuitive. The counterintuitive predictions of quantum mechanics should be an observable phenomena, and indeed they are. In this talk the intuition is examined and in this paper by the same physicist, Aaron O'Connell, the physics is examined.

So I haven't been posting lately. I have been drowned in opportunities, hit by funding woes, and frankly it feels like my mind is melting. I will probably post more aggregated non-original content, like this post, but I also have lots of ideas and new things I am working on.

Flying is Unsustainable

2011-05-03T05:26:00.000-07:00

Today I am crossing Australia, the Pacific, and then the West Coast by airplane and I feel guilty. You see everything that I do in my daily life to be environmentally friendly is nullified by my airplane travel. Even if I was completely carbon neutral in my daily life the excessive amount of airplane travel that I partake in each year would place me me in the same ranks as the worst polluters in America. According to a green manifesto (also see this description of 'low-energy astrophysics') by astrophysicist P.J. Marshall and others the average energy consumption per day of a person in the U.S. is 250 kWh/day/person. An astrophysicist uses an extra 133kWh/day/astronomer, yet the vast majority of that additional energy usage, 113 kWh/day/astronomer, is contributed by flying. The key message of the manifesto is that while astronomers are not actually a significant energy consumer in the U.S. (they use 0.001% of the national total energy production) we are high profile scientists who must set an example. Astronomers believe global warming is real, and thus must act.

Astronomy in Western Australia

2011-04-30T03:33:00.000-07:00

Murchison, AUSTRALIA - Building a radio telescope is nothing like working on an optical telescope, except that both bring you to remote areas. Western Australia reminds me of the Texas hill country. I grew up in Texas and as simple as I can describe it Western Australia is like an upside down Texas. And the people they are nearly the same: they have thick accents, more land than they know what to do with, and national pride. It is hard to describe everything so here are a few pictures of what I have seen out here.

This is a massive 12 meter radio dish from the experiment next door. Western Australia is perfect for radio astronomy. There are very few people and no radio stations to interfere with the data. Several other projects, most importantly the Australian Square Kilometer Array Pathfinder (ASKAP), are very nearby to the Murchison Widefield Array (MWA). Australia is pushing to develop an infrastructure and technical knowledge base in a bid to host the Square Kilometer Array which will be the ultimate next generation radio telescope.

A Bungarra has come to visit MWA! A Bungarra or Sand Goana is a type of monitor lizard common in this part of Western Australia. They are big critters with a swaggering gate and curious yet skittish attitude. This one was wandering around our site for some time. I think he was as equally curious as to what we were doing as to I was about what he was doing. The big white box is a receiver that takes input from the antennas which we were testing.

The self reliant mind set is necessary out here. I am on what an American would call a ranch, but what they call a station. The stations muster, or as I would say drive, thousands of head of cattle and sheep to turn a profit. We were driving along the road one day on our 40 kilometer commute from the station to the antennas when we came upon this airplane. The station manager flies it around to help spot and muster the livestock because it is one of the only ways to find anything on 900,000 acres of land. There are lots of subtle differences to the stations round here to what I would expect in Texas actually. For example there are kangaroos instead of deer, and they don't use horses to muster they use dirt bikes.

This image is a track left by a Bungarra marching off into the distance. Long before the scientists, engineers, or even the ranchers converged onto this remote land an indigenous population known as the Wajarri lived here. Bungarra and their eggs were, or rather still are, a source of food for these people. The Wajarri, like other Aboriginal peoples in Australia, have a different cultural background which is hard for myself and many other westerners to comprehend. What is clear to me is that ancient wisdom still matters in this modern world because humans have a tendency to overreach; technology allows us to do many things, but what should we choose to do? The Wajarri people seem to agree that we should do astronomy as they have allowed us the use of their land for radio astronomy. Perhaps a desire to understand our place in the Universe is a shared cultural value.

A Primer on Radio Astronomy from Australia

2011-04-25T04:09:00.000-07:00

Murchison, AUSTRALIA - I am seemingly in the middle of nowhere, and yet I do not doubt that the Murchison Widefield Array (MWA) is at the center of the Universe. Australia is beautiful out here. The area is surprisingly green because of recent rains and the sunsets are a mix of pastel reds and blues. At night the sky is filled with shooting stars and the Milky Way cuts through the sky so bright that dust lanes and nebula, like the Cosack Nebula, seem to have been painted in black on top of the band of stars in our galactic plane. The radio sky as the MWA sees it would look very different. In order to grasp what the MWA does we will have to first explore what radio astronomy and interferometry is.

Radio astronomy is the alchemy of astronomy; shrouded by secrecy and perpeputated by false claims of being able to transmute raw data into gold. There was a time when radio astronomy was really hard, and that time is always, but technology is making new things possible. The Murchison Wide Field array that I am working on here in the outback is only one of the many next generation low frequency radio telescopes coming online or planned such as LOFAR, LWA, and others.

Modern astrophysicists can observe the Universe using light, particles, or (hopefully) gravity waves. Classically astronomers observed light through a telescope, but today we don't look through telescopes and we don't just vaguely see light; we precisley count photons from every part of the electromagnetic spectrum. Light is made of photons, but a photon can be thought of as a wave and a particle. Indeed, a photon is a wave and a particle at once. Longer wavelength photons have lower energy and lower frequency compared to short wavelength photons. In the radio regime of the electromagnetic spectrum the particle view of light is not very helpful, in fact many radio astronomers and engineers actually neglect to ever think about about photons and only consider wavelength or frequency. Radio astronomers view light as an electromagnetic waves impinging upon our patient antennas like waves on the beach.

Long wavelength photons come from some very interesting sources in the sky. Radio waves certainly come from the Sun, because the Sun emits some energy at just about every wavelength. Radio waves are also emitted by galaxies, pulsars, and neutral hydrogen (through the 21cm line). However, the wavelength of photons is not constant: it increases as the photons traverse the Universe due to cosmological redshift such that more distant objects are seen at progressively larger and larger wavelengths consider to more and more distant objects. In my research I am particularly interested in studying the distribution of matter in the Universe at the largest of scales and at the earliest epochs when there was an abundance of neutral hydrogen. Radio waves are perfect for studying these phenomena, but it is difficult to build a telescope that can see a widefield of view, can see a wide range of frequencies at once, and has good resolution.

As radio waves arrive at our antennas we can either immediately detect them or we can reflect them to a receiver. The Arecibo telescope in Puerto Rico is reflector type telescope, as are the antennas in the Very Large Array. The antenna on your car directly receives the electromagnetic wave because it induces an oscillation in the field inside the metal of the receiving antenna and then you can hook up a transistor, and a speaker - that is a radio like in your car.

The problem with detecting radio wavelengths is that they are not easy to catch and they act way too much like a wave. Waves have strange properties such as interference and diffraction. It can be shown from wave theory that a telescope of diameter D receiving light of wavelength λ has a fundamental angular resolution limit proportional to λ/D. For example the colossal 300 meter diameter Arecibo telescope can only resolve objects down to 3.5 arc minutes (or about half a degree) at a wavelength of .2 meters (or 1.4 Ghz) and that resolving power will only get worse as we move to longer wavelengths. So if you want to see small things in the sky you had better have a huge radio telescope. But wait, there is more. The field of view that a radio telescope can see is also proportional to λ/D. For example at a wavelength of .2 meters it would take Arecibo about 10 separate observations to make an image of the full moon which is about half a degree in the sky.

So if you want to look at the radio sky at high resolution you had better use a huge telescope, but if you want to look at the radio sky in huge swaths, like in survey, you had better use a small telescope. It would seem to be that we are at an impasse to find a decent resolution and decent field of view radio telescope. Enter radio interferometry.

The diagram above is a pictorial representation of the principles of radio interferometry. In box A we have a big radio dish like Arecibo and a radio wave incident upon it. The radio waves hit the dish and reflect to a receiver (not shown in the cartoon) at the focal point. In box B we have chopped our radio telescope into little bits and so while the dish would behave as a smaller dish it would operate via the same principles. Each part reflects the radio waves incident upon it to a single focal point. In box C we have moved the pieces of the dish into several independent dishes and wired them together. Each dish now has its own focus, field of view, and angular resolution limit (this setup is similar to the VLA). Finally, in box D we have gotten rid of even the dishes. Instead of turning the dish to point to a particular object we use the time delay due to the finite speed of light to 'point' the antennas. An object in the direction θ in the sky sends out radio waves that arrive at the antenna tilted. So to catch the same the wave on the antenna on the left and right spanning the arrow in the diagram we use the time delay τ. In this setup there is no pointing the dish there is only an electronic control of simple antenna elements; this is how the MWA works.

The most difficult part of pulling the telescope apart is reassembling the signals coherently. In the diagram this is the function of the box with the circle and x. In radio astronomy that box would be a complex supercomputer and is called a correlator. The computing power needed to operate a correlator scales as the number of antenna elements squared thus it really takes a powerful computer to operate an array with many antennas. The idea is that the signal from each pair of antennas is correlated together to determine the pattern of incident radio waves. This is the basic idea of radio interferometry; the beautiful thing is that you get the large field of view that each antenna would see and the excellent resolution that the large diameter of antennas provide. The description I have given here of radio interferometry is wildly simplified.

So here I am in a shed in Murchison. A generator is humming along and powering all our computers and equipment and importantly the air conditioner keeping me cool. Flies and strange insects pester us relentlessly the moment I step outside. There are a lot of great things about Australia, but it is also a very harsh environment out here. The array has not been cooperating perfectly: there are amplifiers, attenuators, analog to digital converters, correlators, and more that all have to act in symphony for the system to work. The last few days we have solved as many problems as we have created. The radio sky sends its nite rote down upon us and waits for us to complete the instrument.

Scratching the Surface

2011-04-20T08:53:00.000-07:00

Perth, Australia - I found myself in a coffee shop in downtown Perth today just as I would likely of been in Seattle. It was as if I were in a parallel dimension and indeed I talked about parallel dimensions with some new friends I met. I asked them about places in Perth and they asked me about the Universe; I think I learned as much about Perth as they learned about the Universe.

I walked north towards a pub they recommended, but on the way I discovered something much more interesting. I stumbled upon the Scratching the Surface art show. It was a visual art gallery opening by several young artists just beginning to make they mark upon they world, or as they said just scratching the surface. I was walking along the street when I took a double take upon seeing book pages folded upon themselves in a mysterious manner. It was Pascal Proteau's work from recycled books. One of the most imposing works was a massive balance of books holding upon itself a crooked balance of folded book pages.

Nathan Brooker presented a series of works that were reminiscent of Andy Warhol in their repetition and bright colors. Some of his work was shocking. The image below is tame, but the Nathan did many more interesting things which cannot be shown (here is a seriously not safe for general consumption, very intense and shocking do not click here if you don't want to be offended image of Booker with art).

There was lots of shocking art including strange embroidery by Carla Adams. She used homely materials to create dangerous and daring works. I assure you that the image here is the most tame possible from the work she had on display. I asked her what had turned her mind to think of such juxtaposed concepts and she said that it was exactly that, the juxtaposition itself of feminine handy work and male homosexuality.

I was drawn in by the strange folding of books, but it was Ian Williams piece that really stole the show for me. He called it 'Under the Influence', but whatever the influence was it was inspired. An acrylic on oil board piece it was a work of labor as he told me it was painted with acrylic then sanded down then painted again. The entire piece had a subtle checkerboard texture pattern which resulted. And the eyes. The eyes followed the viewer from every angle. This piece was also amazingly large (1.8 by 1.2 meters) which added to its captivating features. It was a stunning piece. He is a talented artist.

Finally, here is a piece of art created just this evening by a friend who I know only as Silvia. She was an art student at the same school in Perth (CIT) as all the artists featured above. I went to a bar (with the aptly artistic name Ezra Pound) with her after the art show and she drew this for (or rather of) me.

It was a strange day in a strange place, but it was fantastic. Tomorrow, I head north into the desert and the Outback.

Australia Trip to Murchison Wide Field Array

2011-04-14T23:50:00.000-07:00

I am going to Australia for two weeks on Sunday to work on data collecting and commissioning of the Murchison Widefield Array (MWA). The MWA is a next generation radio telescope being built in the radio free void of Western Australia. The radio sky is a largely unexplored area of astronomy. The radio sky holds many exciting scientific prospects and by observing it we can learn about cosmology, the first stars, our Sun, galaxies, the structure of the Milky Way, pulsars, dark matter, and dark energy. Studying the sky in radio wavelengths is tricky because of the complex electrical engineering problems its presents and the sheer computing challenge which arises from the fact that each antenna must be correlated with every other antenna thus thus computational cost of adding antennas goes as the number of antennas squared. Currently we have 32 'antennas' out (already more than the VLA); each antenna actually consists of 16 dual polarization dipoles (seen below in the image). The final MWA layout will have 512 antenna tiles with 8192 dipole elements sensing the sky in the frequency range of 80-300 MHz. We have already generated some fantastic images of Centaurus A and other fields, but I am not sure what images I am allowed to release. In the next two weeks I will write up what I am up to in my Australian travels and hopefully I will post some never before seen images.

Nostalgia de la Luz

2011-04-05T01:55:00.000-07:00

The present does not exist. All notions of the present are built upon the history of light. Patricio Guzmán's makes these surreal claims as he narrates in his documentary Nostalgia de la Luz (or Nostalgia for the Light) as he draws out the connections between astronomers and those searching for bones in Chile's Atacma Desert. Guzmán is obsessed with history and talented at drawing strange parallels in this compelling film. Chile under the rule of Pinochet in the '70s has a dark history of kidnapping, concentration camps, and mass murders of political dissidents. Chile also has clear dark skies which astronomers have fallen in love with.

I saw this film this evening and I was impressed. It takes one of the best parts of astronomy and projects it on to a real human conflict in a way that is scientifically tasteful and touching at once. There is a lot that could be said about the film and the director as well who was in exile from Chile in the '70s, but there is an easy way to summarize the film: the most profound questions about the Universe and human existence are the same. However, this summary doesn't do the film justice as it uses strong imagery to evoke what can't be said. I did not know that the half illuminated moon and a human skull looked so similar. In the end though you are left with the realization that those searching in Chile's deserts will not be able to change the past.

Naming the Unknown #1

2011-03-25T19:47:00.000-07:00

Naming the Unknown is a new series where I highlight interesting papers in astrophysics. Research papers which I find compelling or of general interest will be spotlighted. The title 'Naming the Unknown' comes from accusation that cosmologists have simply begun to come up with names for those things which are not understood; yet, I do not think that anyone would claim that science is at times anything other than coming up with names for the unknown. Scientists define the unknown in terms of the other unknowns and as time passes the first unknown has a context, but ultimately all we have a is a self referential group of symbols that isn't necessarily any more logically sound than where we begun. The relation of fundamental particles (μ⁺ compared to a π⁺, obvious relation no?), the definition words in a dictionary, and all information suffers from the flaw of self referential formalisms. I digress. On to the first paper.

* * *

Fermi Bubbles: Giant, Multibillion-Year-Old Reservoirs of Galactic Center Cosmic Rays. Roland M. Crocker , and Felix Aharonian. DOI: 10.1103/PhysRevLett.106.101102

The Fermi telescope recently discovered evidence for giant gamma ray lobes associated with our Milky Way (you should see my first posted about the Fermi Bubbles here if you are not familiar with this remarkable discovery). The original paper on the Fermi bubbles was an observation description of the evidence for the bubbles; it was found that there are lobes extending above and below the plane of the Milky Way symmetrically with an extent of ~10 kpc and a unique energy spectrum. Several possible formation scenarios for bubbles were put forward, but no single theory was advanced a definitive. In a paper published this month in Physical Review Letters Roland Crocker and Felix Aharonian conclude that the bubbles are naturally explained due to a population of relic cosmic ray protons and heavy ions injected into the bubbles by high density star formation in the galactic center.

There are two general lines of thought as to the source of the bubbles. In one scenario the black hole at the center of our milky way is somehow responsible for the gamma ray lobes. The black hole paradigm can further be broken down into two sub-categories: tidal disruption of a star and active galactic nuclei.

The tidal disruption of a star occurs when the super massive black hole at the center of our Milky Way, Sagatarius A*, disrupts, or basically eats a wandering star. The tidal disruption of stars by black holes is viable and certainly does occur (see work by Guillochon et al. 2009) with the release of energy, hot plasma, wind, and shocks which could heat up the halo and produces thermal x-rays (see ongoing work by Cheng et al. 2011, unpublished). However, this explanation for the Fermi bubbles is slightly ad hoc and it would have to occur on a periodic basis to account for the bubbles.
Saggatarius A* is dormant now, but if a star cluster or gas cloud fell/accreted into it in the past it may have undergone an active galactic nuclei like phase which could emit sufficient radiation and cosmic rays to explain the bubbles. This active galactic nuclei scenario would also have to occur periodically (10 million years or so) to explain the presence of the bubble.

Lets forget super massive black holes and look at a simple alternative. Crocker and Aharonian invoke ongoing star formation in the galactic center to explain the hard-spectrum, uniform intensity, vast extension, and the energetics seen in the bubbles. Extremely long time scale star formation (on the order a billion years) will have with it an associated cosmic ray population which will be injected into the bubbles by a wind. Cosmic rays are hadrons (mainly protons and some heaver ions) accelerated by non thermal process such as supernovae shocks which move at extremely high velocities and thus carry lots of energy. The cosmic rays will lose energy primarily though collisions with other protons (pp collisions) in the low density plasma of the bubbles and subsequently produce gamma rays electrons, positrons, and neutrinos (intermediate meson particles are also created). This would explain the gamma ray emission at >100 Mev seen form the galactic plane. Under many conditions this kind of gamma ray emission would be expected to trace the underlying ambient density of matter with which the cosmic rays are colliding with, however, in the case of the Fermi bubbles the time scale for proton collisions and time scale for the particles to escape from the system are comparable. The bubbles would be a saturated system wherein the gamma ray luminosity is only proportional to the power injected independent of the gas density; this is a vital point in explaining the morphology of the lobes: they have a hard spectrum out to their edge and then end abruptly.

Based on IRAS satellite data the galactic center star formation rate is ~0.08 solar masses per year in turn implying a rate of ~0.04 supernovae per century. These supernovae inject power at a rate of 10³⁹ ergs per second into cosmic rays. These cosmic rays are removed the from the immediate vicinity of the galactic center and transported into the bubble regions by a super wind generated by the ongoing star formation and supernovae themselves. A wind such as this is observed commonly in many other star forming galaxies such as NGC 3079. The wind speed is ~1200 kilometers per second and has sufficient velocity to escape locally, but it has been shown that the wind should stall at a height less than ~15 kiloparsecs above the plane and this would explain the exact height of the bubbles.

That continuous star formation (and subsequent supernovae) could be responsible for the Fermi bubbles is an Occam's razor kind of solution. It reproduces a number of observations seen in the bubbles and predicts some further properties. For example the electrons and positrons which are created along with the gamma ray emission will synchrotron radiate because of ambient magnetic fields with a luminosity of ~10²⁶ ergs per second which is exactly what is seen in the 20-60 Ghz band by the WMAP satellite (the so called WMAP haze). This kind of after the fact observation is not so impressive, but the authors make various predictions which will be testable in future observations.

***

A large aside on the mess of publishing, press releases, and open access. When NASA made the press release on the Fermi bubbles and I first blogged about them I stated that I didn't have anything to go on besides the press release because no paper was available. How wrong was I! The first paper was published in The Astrophyical Journal, titled Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?, in November of 2010 (at the same time as the press release), but it was posted on the arxiv on the 29th of may 2010. This paper I mentioned here today was published the 16th of August 2010 on the arxiv and then published just a few days ago in March in physical review letters. It is astounding how long the peer review process took for each of these papers, but it is deplorable that NASA doesn't make readily available links to the actual paper. I could have told you about the Fermi bubbles and given a natural explanation for them about a year ago if I had been on top of this.

References

Crocker, R., & Aharonian, F. (2011). Fermi Bubbles: Giant, Multibillion-Year-Old Reservoirs of Galactic Center Cosmic Rays Physical Review Letters, 106 (10) DOI: 10.1103/PhysRevLett.106.101102

Double Rainbow

2011-03-21T21:28:00.000-07:00

The Ring Nebula (M57) versus the Morning Glory geyser pool at Yellowstone National Park. How is that they look so similar? I can answer that.

M57 was once a star like the Sun which exhausted its hydrogen fuel and puffed up into a red giant giving off winds; it is a planetary nebula. At the center an aging super hot star emits ultraviolet radiation exciting the nearby gas the most thus giving off the blue color. Towards the edge the gas is cooler and appears red. This is a real color image. View M57 with even a pair of large binoculars (3 inch) and it will look like a smoky ring, moving up to a larger telescope the colors and structure will become visible.
The Morning Glory pool is a hot spring in Yellowstone National Park. It is an upwelling of water geothermally heated by the Earth's tectonic activity. The water at the center is blue because of the intrinsic color of water (it preferentially absorbs red light) and the depth at the center of the pool. At the edges of the pool bacteria in microbial mats grow (bacteria are absent in the center because of the lack of light and high temperatures). The color of the bacteria is determined by the amount of pigments in them particularly chlorophyll and carotenoids. This is a real color image (also see this even more vibrant picture of the Morning Glory Pool). Perhaps, life started in a hot bubbly pool like this on the primordial Earth.

Wow, these phenomena are self similar in their optical, geometric, and thermal properties. I will leave it as an exercise to the reader as to answer why nature is so amazing.

A Universe From Nothing

2011-03-12T15:36:00.000-08:00

Lawrence Krauss speaks humorously and frankly on cosmology. This talk is filled with insights on how we came to our remarkable knowledge of modern cosmology. I especially enjoy the opening quote:

The initial mystery that attends any journey is: how did the traveler reach his starting point in the first place. ~Louise Bogan

100 Images of Macchiatos

2011-03-10T22:31:00.000-08:00

I drink a lot of macchiatos. If you don't know, a macchiato is an espresso coffee 'marked' with steamed milk.

You can see a larger version here. I work in coffee shops almost daily here in Seattle, and over the last year or so I took these pictures of each drink I had. Each coffee shop and barista has a different way of making the drink and I didn't take each picture in any particular way to standardize them, but I really like the result: a collage of consumption of coffee: 100 images of macchiatos. A little while ago I posted Thirty Five Images of Space Helmet Reflections which was a similar image, alas, while I would like to of been wearing one of those space helmets the reality is that I spend my time merely dreaming of the stars in coffee shops.

Fusion for the Future: NIF

2011-02-25T15:12:00.000-08:00

Fusion is only 50 years away and it will solve all of the worlds energy problems. That is the good news. The bad news is that it has been 50 years away for the last 50 years. If that situation is maddening to you then you are not alone. Leonardo Mascheroni, a retired Los Alamos National Laboratory physicist, wanted funding to build a colossal laser for producing energy from fusion and was willing to trade the United States' nuclear weapons secrets to realize his dream. Mascheroni was recently indicted on charges of treason concerning selling nuclear arms secrets and is awaiting trial sometime this year. In the meantime the United States is pressing forward with a completely separate laser fusion project called the National Ignition Facility or the NIF which uses 192 lasers fired in unison to recreate the energy source of the stars harnessed on Earth.

In this post I am going to talk about the basics of fusion and the NIF. I also have questions and answers with a physicist on the project, Siegfried Glenzer, at the end of the post. I asked him some hard questions not just about the science, but also about the politics going on around the project. Physicists would like their experiments and budgets to work in a vacuum, but alas they never are. I deeply thank doctor Glenzer for answering my questions.

What is fusion?

Fusion is the joining of two or more separate atomic nuclei into a larger nuclei. Fusion can create energy because the mass of the input and output nuclei are not necessarily equal in mass. Specifically, if the mass of the output nuclei is less than the total mass of the input nuclei then the mass difference is made up by the production of energy as Einstein taught us E=mc² (conversely if the output nuclei are more in total mass than the input nuclei then the reaction would consume energy). In particular, stars like our Sun fuse lighter elements into heavier elements up until the point the star is attempting fusion of iron which does not produce energy because iron has the largest binding energy per nucleon. Actually fusion processes in stars normally involve several intermediate nuclei or elements. The most important process for our Sun is the proton-proton chain which fuses four hydrogen nuclei, ¹₁H, to form a single helium nuclei ⁴₂He with a mass difference of ΔM. Einstein's mass energy relation shows us how much energy this process releases.

4 ⋅ ¹₁H -⁴₂He = ΔM

ΔM c² ≈ 27 MeV

The key to joining two nuclei together is overcoming the repulsive electric Coulomb force between nuclei. The positive charge on nuclei repel each other until the two nuclei actually meet and then the attractive short range strong nuclear force takes over to bind the two nuclei into new larger nuclei. The fewer the number of protons in the nuclei the easier it is to fuse. The repulsive force between nuclei may be overcome in several ways. Inside stars heat and pressure, which comes from the stars gravitational contraction, occasionally forces two nuclei close enough together for them to fuse and all together the star burns consistently for a very long time. The more massive the star the hotter and denser it is at the center so larger nuclei can be fused. The production of heavier elements by stars fusing hydrogen is essentially the origin of all elements heavier than lithium; massive stars occasionally explode, and thus we are all made of stardust. The input elements for the first fusion reactors will be the hydrogen isotopes of deuterium (H with a neutron) and tritium (H with two neutrons) because this reaction has the highest nuclear cross section and high energy yield.

Why is fusion important?

Fusion is very important; this is the kind of physics that future presidents should understand. In this post I am focusing on the basics of fusion and the prospects for the National Ignition Facility and a in a future post I will talk about another project known as ITER. I should clarify that there are effectively many different kinds of fusion machines and an important distinction is net energy positive and net energy negative machines. The ratio of fusion power to input power (often denoted Q in the field) must be positive to have a viable energy solution. There exist at this moment very many fusion machines which take more input power than they make in output power (they have a fractional Q value). Some of the current machines seem fantastic like 'table top' pyroelectric fusion devices, but the reality is that they take energy to run and have no foreseeable future in the energy game. These devices play a role as portable neutron generators in labs for various research purposes or in security as nuclear material detectors. Net energy positive machines have not yet been invented. The NIF will not produce energy, but will be a testbed for fusion technologies. The fusion technology goal is the sustainable production of energy from abundant raw elements such as hydrogen, helium, or related isotopes (Helium 3, deuterium, tritium). Fusion using these light elements is cheap, safe, and green. Fusion is cheap (however the technology development is expensive!) because the raw elements like hydrogen are abundant, further as a consequence of this virtually infinite supply (one in every 6,500 atoms on Earth is a deuterium atom) it can be considered a renewable energy. Fusion is safe because when a fusion nuclear reactor malfunctions unlike a fission nuclear reactor the reaction will snuff itself out rather than proceed uncontrollably to the point of a thermonuclear explosion. Finally, fusion is green or environmentally friendly because it produces no climate altering products.

There are so many reasons fusion is important. Fusion is the future. It is the next step in humanity's technological evolution. This video from the BBC Horizons series with physicist Brian Cox gives a cursory look at the NIF, and puts the entire endeavor into perspective (and to boot in finishes with The Kinks This Time Tomorrow which has the most appropriate lyrics ever).

How do we use fusion to make energy?

Under the correct conditions of incredibly high density, pressure, and temperature a self sustaining fusion process can occur. These conditions are of course exactly what you find at the center of a star, but on Earth these conditions are engineered via the use of confinement and heating mechanisms. The NIF will use a symphony of lasers to simultaneously heat and compress a pellet of deuterium and tritium to simulate the conditions inside of a star. A deuterium and tritium target has been chosen for this first experiment because the fusion cross section between deuterons and tritons is three orders of magnitude larger than for any other atoms. Other fusion projects like ITER will use a toroidal (or doughnut shaped) chamber known as a tokamak to confine a deuterium and tritium plasma which is then heated through magnetic field confinement or radio frequency heating kind of like a big nuclear microwave. Once the fusion process is begun radiation and fast neutrons will be emitted which will be absorbed by the walls of the machine in order to gather heat to drive a steam-turbine generator to produce electricity pretty much just like every power plant.

How does NIF work?

It all starts with a single primordial laser source with very low power which is slightly preamplified and split into 48 parts. These pulses are then amplified by a factor of 10 billion in another set of preamplifiers then they are split into 192 parts and sent to the main amplifier. Then electrical energy stored in capacitors is dumped into 7680 xenon flashtubes which operate pretty much like the flash on your camera, except they are over 6 feet tall and take 30 kilojoules of input power each. The bright incoherent full spectrum light from the flashtubes passes through Neodymium doped glass and in a stupendously inefficient process amplifies the laser beams. The lasers bounce back and fourth a few times and finally go through the amplifier and the main optics system again before heading to the target chamber. At this point the primordial laser has been amplified by a factor of 10¹⁵ (in the video below he says quadrillion which apparently doesn't even have an agreed upon meaning, I think 10¹⁵ is right). The beams travel equidistant paths into the final optics assemblies which convert the original infrared light in to UV light that enters the target chamber. Inside the chamber the light focuses onto a little cylinder called a hohlraum and then, maybe, fusion starts. This process is very complex, this video explains it way better than I can.

Finally the lasers converge in the center of the laser chamber on the hohlraum. What is a holraum and what happens next? This was one of the questions I asked Dr. Glenzer and he responds,

A hohlraum is a radiation enclosure. The laser irradiates the inside of the hohlraum wall and is converted to soft x-rays. The soft x-rays homogeneously ablate the outer layer (the ablator) of a 2.2 mm spherical fusion capsule in the center of the hohlraum. Due to Newton's third law, the dense fuel on the inside the ablator layer is accelerated towards the center producing a hot plasma surrounded by dense deuterium and tritium (1000 times solid density). The center will get very hot launching a burn wave into the dense deuterium-tritium layer: A microscopic star is born.

This is in theory, exactly what happens. The 192 lasers induce densities and temperatures sufficient for nuclear fusion by not allowing the spherical fusion capsule to explode asymmetrically (technically this is called internal confinement fusion). The rate of fusion is proportional to density squared times the temperature to the fourth power, so the more rapidly the capsule can be made to implode the better. In reality the lasers impending on the capsule will create an imploding shock which will cause instabilities to grow under high acceleration of the shell during the convergence and allow energy to escape ruining the efficiency of fusion. Compression is maximized by keeping the fuel cool hydrodynamically with several laser pulses stepped in time such that the spherical deuterium and tritium fuel capsule is qausi-isentropically compressed. When the deutrieum and tritum nuclei get close enough for the strong force to kick in fusion results in 14 MeV neutrons and 3.5 MeV alpha particles being emitted. The 3 MeV alpha paricles have a short mean free path in the dense enviroment which causes local heating and facilitates sustained fusion.

However, no one has ever measured the dynamic compression and shock breakout pressures present in the shell and the nonlinear nature of the process means is must be determined experimentally. There is no equation anyone has to say how this is going to work because the system is so complex. An example of one specific issue the physicists at the NIF face is the so called Rayleigh-Taylor instability that originates from the interface between the solid shell and the deuterium and tritiutm fuel within it. It is this instability which causes the fusion reaction to proceed asymmetrically such that the necessary temperatures and pressures are not reached because instead the capsule explodes before the implosion is complete. Overcoming physics challenges like this will lead to efficient fusion.

Politics at the NIF

The politics of the NIF are as complicated as the fusion itself. The project is wildly expensive so that alone makes it controversial and beyond fusion the NIF has a second major task that doesn't fit in their public relations campaign so well. The NIF will provide needed data on the nuclear weapons status, capability and performance in this era of nuclear weapon testing abstinence. The United States has a stockpile stewardship and management program run by the DOE which tests nuclear weapons, but it can't go around nuking like it used to as a result of the comprehensive test ban treaty established in 1996 (edit: the United States has signed but not ratified this treaty, regardless live nuke testing is frowned upon in the modern age) . The NIF should be able to experimentally simulate on small scales the conditions of pressure, temperature, and energy density close to those that occur during a nuclear explosion. I have never read anything that describes how the NIF is meeting these goals in technical terms information is tight. As for our would be spy, Mascheroni, the evidence regarding his case was placed under a limited protective order by a judge last Tuesday. Documents containing sensitive nuclear weapons information will be crucial in his case, but, like so much else at the NIF, confidential.

Hope for the NIF

The NIF has everything: science, intrigue, spies, money, and hope. The hope is that it leads the path forward to sustainable fusion. The issue currently is that there is a physics and engineering problem at the NIF and based on what is known today it seems unlikely that NIF will produce any practical amount of fusion energy because it wasn't designed to. It is a scientific experiment which will give us answers about fusion. It will light a path forward, literally, with the power of the stars.

Questions and Answers on the NIF

I leave you with some questions and answers with Dr. Glenzer.

1) What are the design challenges of the NIF?

The NIF laser is finished and operational. At this point, we can deliver more than 1.2 MJ energy and 400 TW (yes, 400 TW) on target and we have calculations that indicate a good chance at ignition at these energies if everything else works as expected.
One of our goals is to increase the laser energy and power further to 1.8 MJ and 500 TW to increase ignition margin. This requires careful placement of beam smoothing optics and proper planning of optics maintenance. We are in the process of implementing this capability while we are doing experiments in the facility every day. A very challenging task.

2) What does focusing lasers at a hohlraum with a deuterium-tritium target at the center do? And what is a hohlraum?

A hohlraum is a radiation enclosure. The laser irradiates the inside of the hohlraum wall and is converted to soft x-rays. The soft x-rays homogeneously ablate the outer layer (the ablator) of a 2.2 mm spherical fusion capsule in the center of the hohlraum. Due to Newton's third law, the dense fuel on the inside the ablator layer is accelerated towards the center producing a hot plasma surrounded by dense deuterium and tritium (1000 times solid density). The center will get very hot launching a burn wave into the dense deuterium- tritium layer: A microscopic star is born.

3) This machine creates a star on Earth?

Yes, a microscopic star will exists for a billionth of a second burning deuterium and tritium into helium nuclei.

4) In an experiment in early November of 2010 a 1.3 megajoule laser shot run produced a world record neutron yield for laser-driven fusion in internal confinement target, thus fusion is being achieved at NIF, yet this is not considered ignition. What does ignition mean and what advancements are necessary to achieve it?

Ignition means producing a burning plasma where fusion processes occur on a much higher rate than observed so far. This is about the case when the energy produced by fusion processes is of the order of 1 MJ, i.e. of the same order as the laser energy used to heat the target.
This is of fundamental interest for laboratory astrophysics and dense plasma physics. To make this process useful for energy production using fusion we are further developing targets that produce about a factor of 100 more energy than initially used by the laser.

5) This machine is designed to do vastly more than just fusion. What other fundamental physics is explored?

The rough split is 40% fusion, 40% defense, and 20% basic science. There are calls for proposals on the NIF website, and Universities around the world have responded to the first call submitting more than 40 proposals. Eight experiments were selected to be scheduled on NIF in the next few years. The proposals include the study of supernovae plasmas or states of matter of ultra-high pressures and densities never produced the laboratory before.

6) The NIF has been accused of black ops, cost overruns, political pork-barreling, and misleading the public on the reality of fusion. Does this situation put additional pressure on the scientists on the project?

I do not believe that there is additional pressure when people are asking critical questions. Fact is that there are fewer world-leading science machines left in the US than before- see LHC in CERN or the upcoming XFEL at DESY. I believe that NIF will make a big difference in science and it will be worth the investment.

7) When will we have sustainable energy producing fusion on Earth?

Good question - I believe that I will live to see it happen (I was born in 1966).

References

Glenzer, S., MacGowan, B., Michel, P., Meezan, N., Suter, L., Dixit, S., Kline, J., Kyrala, G., Bradley, D., Callahan, D., Dewald, E., Divol, L., Dzenitis, E., Edwards, M., Hamza, A., Haynam, C., Hinkel, D., Kalantar, D., Kilkenny, J., Landen, O., Lindl, J., LePape, S., Moody, J., Nikroo, A., Parham, T., Schneider, M., Town, R., Wegner, P., Widmann, K., Whitman, P., Young, B., Van Wonterghem, B., Atherton, L., & Moses, E. (2010). Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies Science, 327 (5970), 1228-1231 DOI: 10.1126/science.1185634

Listening to the Universe

2011-02-23T00:19:00.000-08:00

The enigmatic people at VBS TV just posted a piece on LOFAR, a next generation radio telescope (my own research is on a very similar radio telescope, the MWA, which I will discuss another day). Mother Board, the technology focused side of VBS even has a radio astronomy portal. Radio astronomy has never seemed so cool:

For the longest time, astronomy centered around what could be observed with our most wonderful and yet meager visual tool, the eye. But in the last fifty years, the ability to gaze up into space using radio waves, infrared and ultraviolet radiation and X- and gamma rays have provided new and completely unexpected information about the nature and history of the Universe, yielding a cosmic zoo of strange and exotic objects. But we have yet to properly explore the low radio frequencies, the lowest energy extreme of the spectrum accessible from the Earth. (Astronomers don’t actually listen to the signals, but convert them into data and images.)

With more “resolution” than any other telescope, the 1500 km-wide LOFAR array will open this frontier to a broad range of astrophysical studies, including transient sources, ultra high energy cosmic rays, cosmic magnetism, and the Epoch of Reionization. [more from Mother Board, Listening to the Universe]

I want to give one more shout out to the strange and amazing VBS TV. It is a news source which I have heard described as '60 Minutes meets Jackass' which is a powerful combination whether your watching Shane Smith in the Vice Guide to North Korea or anything from the expansive Vice Guide to Everything so please check it out.

Man vs. Machine: Computable Knowledge and Language Processing

2011-02-19T12:46:00.000-08:00

Computers have come a long way since Charles Babbage's time. Babbage was the inventor of the concept of the programmable computer. He designed and attempted to build several machines including the Analytical Engine which was a programmable mechanical computer. It would have been the first Turing-complete (roughly implying it can simulate any other computer or proper program) machine ever. People at the time were confused by the entire concept of a computer.

"Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.

People thought that if a computer could do calculations it must be smart in the same way a person is smart, that is make deductions, inferences, and synthesize information to make conclusions. In the 1960's computers showed great promise and some researchers thought the age of truly intelligent machines was just a few years away. It turned out that the human mind is formidable opponent. Machines which think exactly like humans may not ever exist, but machines that 'think' are already here.

The final question, "William Wilkenson’s 'An Account of the Principalities of Wallachia and Moldavia' inspired this author's most famous novel." All contestants got the question right, but Jenning's knew he was not catching up.

Humans and machines were doing a lot of thinking this week when humans faced off against computers in a three day exhibition Jeopardy! match. The computer in the match was called Watson which was able to defeat Ken Jennings, the winngest ever Jeopardy player, and Brian Rutter, the all-time Jeopardy money winner. Watson is a purpose built technology demonstrating computer built by IBM which uses language processing and machine learning to play Jeopardy. A very good documentary produced by NOVA is available online which discuss the research and development that went into Watson, The Smartest Machine on Earth, which is a good watch even if you have been following the news on Watson. In the three day match things began slowly as Watson held is own, but occasionally stumbled. However, in the end Watson was light years ahead. Here is the recap:

This isn't the first time a human vs. machine battle has been played. In 1997 a highly publicized battle occurred between world chess champion Gary Kasparov and IBM's Deep Blue. Kasparov fell hard in the battle and even accused IBM of cheating. In retrospect his protests were in compete futility, as is proven by the fact that in 2006 world chess champion Vladimir Kramnik was beaten by a computer, Deep Fritz, running on a standard personal computer (running two Intel Core 2 Duo). Chess playing computers are not too 'smart'; they basically use their computing power to play out likely board configurations and so the techniques employed by chess playing programs have been excluded from some definitions of artificial intelligence. And of course maybe Watson isn't that smart either you could say. Watson uses knowledge humans have gathered, finds patterns, finds the relative strength of each answer, and returns the answer. It is hard to exactly define what intelligence is so I won't even try. Instead I will make two observations about the implications of machines besting humans. First, what takes a super computer at one point, will take a microchip in the future as indicated by the evolution of chess playing computers. Second, while the argument about what intelligence is goes on the pace and ability of computers also goes on.

How does Watson think? Watson uses machine learning. Basically Watson is fed a bunch of text documents like Wikipedia and IMDB (note that Watson was not online during the Jeopardy competition, but had access to these documents pre archived). Then programmers feed Watson questions and correct answer pairs which Watson can use to look through its database to find patterns. A complex architecture of rules and statistics allow Watson to choose the right answer, but amazingly programmers on the project don't explicitly tell Watson how or what the right answer is. Modern computer programs are big and complicated so it is best to let the computer take care of writing their own programs.

Watson's success means there is a bright future for language processing computers (at least IBM wants us to think so and buy their products). I have been contemplating the merger of Wolfram|Alpha and IBM's Watson as the ultimate language processing computational engine. Alpha if you have never used it is a live web program that anyone can use. The creator, Stephen Wolfram, calls Alpha a computational knowledge engine. This means that Alpha doesn't parse language in the most human receptive manner, but it has powerful database and computational algorithm resources such that if you want to know the error function of the GDP of Italy divided by the GDP of the US all divided by the 144th prime, well you can do that. Also, Alpha can do math, and how. IBM's Watson on the other hand could tell you the name of the country with its boot dipped in the Mediterranean. These smart computers are different for obvious reasons, they have access to different information databases and they are programed differently. An explanation of the difference recently came up on Stephen Wolfram's blog in pictorial form.

It would be a powerful combination to have Alpha's database and analytical skills paired with Watson's language processing. Perhaps we will have a Watson|Alpha soon. I remarked to a colleague in jest the other day that if they made such a machine I would be out of a job, but he replied that I would still have job as long as computers only have answers and not questions. True enough. I am reminded of the Hitchhikers Guide to the Galaxy where an immense computer calculates the answer to the universe, however, with the answer in hand it is realized a bigger more powerful computer must be constructed to determine the question.

The Universe and Life is asymmetric: Chirality

2011-01-21T17:40:00.000-08:00

The shadow of symmetry haunts physics. Symmetry is invoked to understand nature concisely, but broken symmetry is invoked to understand nature completely. Physics is filled with examples of shattered symmetries: there is more matter than antimatter, neutrinos only come in the left handed spin flavor, and quantum processes break symmetries constantly, but nature also violates symmetry in chemistry and biology in a very clever manner. Chemistry and biology are subjects I do no normally touch upon, but I am intrigued by the curious circumstance of life on Earth: many molecules are not superimposable upon their mirror images, a property called chirality, and life on Earth has a preference for these chiral mirror configurations. Physics and life is inherently asymmetric.

That something is not identical to its mirror image is a property known as chirality. Hands (etymologically the word chirality is derived from the Greek word for hand), spiral galaxies, and the DNA helix are all examples of chiral objects. In particle physics chirality is actually an abstract notion defined by transformations of the particle with respect to their right of left handed representation in the Poincaré group. In chemistry chirality is well described by analogy to your hands wherein left and right hands cannot be superposed on each other even though the fingers are the same and match up.

This article is an exploration of chirality in biochemistry. I want to ask what makes life chiral, why is life chiral, and how did life become chiral. In order to supplement my limited knowledge of the subject I interviewed a world expert and author of over twenty papers on the subject, Robert Compton, who I must give a deep thanks to for being willing to answer my silly questions.

It is important to accept that the concept of symmetry is tinted by the human notion of harmonious or aesthetically pleasing forms, but the strict mathematical interpretation of symmetry relies upon metrics of geometry. To this end many seemingly symmetric forms in the living natural world are actually examples of broken symmetries: spiral tree trunks, the human form, and sea shells (which generally only coil in one particular direction according to species). The remarkable thing is that this macro asymmetry can be traced back to a micro asymmetry in the chemistry of life. The arrangement of atoms in a molecule defines the function of that molecule, but even molecules with the same chemical configuration can behave differently as in the case of chiral molecules which are like mirror images of the same molecule that come in 'left' and 'right' handed forms. The great asymmetry of life is that all living organisms on Earth almost exclusively utilize the left handed (or levorotatory) configuration for amino acids and the right handed (or dextrorotatory) configuration for sugars belonging to DNA or RNA.

Perhaps it is trivial or obvious that life is chiral when looking at the nautilus, but this obvious chirality is a macroscopic feature which belies the fine arrangement of atoms which defines the chirality of biomolecules.

Different structural forms of compounds with the same molecular formula are known as isomers to chemists. A stereoisomer is an isomeric molecule which has the identical constitution and sequence of bonded atoms, but has a different three-dimensional geometry in space. An enantiomer is one specific steroisomer of the two possible mirror images that are non-superposable. The dominance of the left handed chiral enantiomer in biology is a massive blow to the idea that nature is perfectly symmetric and is an unsolved mystery as to why nature is this way.

Many molecules are chiral, however because molecules are constantly vibrating the instantaneous structure of a molecule may lack the exact structure or symmetry seen in an ideal model. Regardless, enantiomers have identical chemical properties except when they react with other molecules which are also enantiomeric in which case chiral forces yield a difference in behavior. Further, and perhaps more important for biology, particularly astrobiology, is that enantiomers have identical physical properties except with respect to the way they interact with plane-polarized or circularly polarized light or other chiral compounds. A pure enantiomer compound will rotate the plane of a monochromatic plane-polarized light by a certain angle in one direction, say clockwise, while the other enantiomer form of the compound will rotate the light by an equal amount in the opposite direction. Things that rotate light are said to be optically active. Measurements with a polarimeter allow chemists to determine if a compound is chiral or not. Polarization of light by organic compounds was discovered in 1815 by the French physicist and chemist Jean-Baptiste Biot. He found that organically produced chemical solutions consistently rotated plane polarized light, but laboratory synthesized chemicals did not reproduce the rotation. Beyond conjectures he had no explanation for the phenomena.Years later Louis Pasteur preformed a similar experiment with tartaric acid produced from grapes and tartaric acid synthesized in the lab. Pasteur went further and somehow used tweezers and a microscope (I do not conceive to understand how) to separate the tartaric acid crystals which he produced in the laboratory into piles of left and right handed molecules. He found that polarized light was rotated by the left handed molecules that he had selected in the same way the polarized light was rotated by the organic tartaric acid. He concluded that chiral molecules are responsible for the rotation of polarized light.

So chiral molecules rotate light, but actually so does an individual achiral molecule! In an ensemble of achiral molecules each individual molecule may rotate the plane of the polarization, but the net rotation averaged over the ensemble will result in zero rotation. A mixture of two enantiomers in a 1:1 ratio (which is what you get when you create chemicals in the lab) is optically inactive because the rotation results in a zero net polarization rotation. When a reagent or catalyst is optically active the chiral product will also be optically active, or in the presence of chiral forces such as circularly polarized light this may also induce optical activity via enantimoeric excess in the products as well. Generally you can get optically active compounds in two ways 1) The reagent in already optically active. 2) The reaction of achiral but optically inactive precursors in a chiral optically active environment occurs. It takes an optically active molecule or chiral force to produce a product that is optically active.

Most chemical reactions are not enantiomerically selective so that the initial reason for a completely homochiral biology on Earth remains a mystery just as when Biot and Pasteur discovered chirality through optical activity. Of course chirality is simply geometric in nature and thus this geometric asymmetry is what makes life chiral. Any molecule that contains a tetrahedral carbon or other central atom bonded to four different atoms or constituents will exist in enantiomeric forms; given that all biological molecules are at least this complicated, then (almost?) all biological molecules exist in enantiomeric forms. It may be that the chirality of biomolcules is simply a consequence of the emergent complexity of basic physics. The conditions necessary for a solution initially containing near equal number of chiral forms to evolve towards pure chirality has been explored (see Frederick Frank 1953) and is plausible. A tiny initial imbalance has spiraled out of control and now each successive generation of biomolecules on Earth is produced by the previous generation of chiral reagents, thus this is the why life is chiral. None of this explains how life is chiral, but a common answer is that because life can be chiral it is chiral.

From this persepctive this topic is not so interesting, honestly. I have come to the conclusion that chriality is as it must be given that each generation of life is spawned from the previous generation under conditions which do have enantiomeric selection forces present. The question is why was left handed chirality chosen for life on our Earth?

Now actually, the chirality of biomolecules is not just a philosophical diversion; it a serious issue of biochemistry in balance. There are over 530 synthetic chiral drugs worldwide today. It is technically and economically prohibitive to make enantiomerically pure drugs in all cases. This results in drugs that may have strange, null, or fatal interactions with human subjects. In some cases the difference between two enantiomeric forms is simple, as in the case of the olfactory exciting chemical carvone; in one configuration it smells like spearmint and the other configuration like caraway seeds. So, "Perhaps," as Alice said to her cat in Lewis Carroll's Though the Looking Glass, "looking-glass milk isn't good to drink".

I digress. Before we hear what Dr. Compton has to say on this matter lets look at what fundamental physics would bias the chirality of life on Earth and how homochirality was selected on Earth. There are three distinct mechanisms that seem plausible.

The weak force. Of the fundamental forces, nuclear, electroweak and gravitational, only the weak force can distinguish between left and right parity particles. The weak force it turns out does not conserve parity (although it does conserve CPT symmetry) during some interactions such as the radioactive beta decay corresponding to the emission of an electron with intrinsic spin 1/2 hbar. Also, the weak force induces a parity-violating energy difference, PVED, between molecules or the interactions of left-handed electrons emitted during beta decay with molecules. So the weak force could preselect a handedness in nature through either beta decay or PVED. The idea is that if one chiral configuration is a lower energy state then nature will prefer that configuration (in fact the exact scaling from thermodynamics is that the reaction rate for the oppositely chiral molecules is proportional to the canonical partition function in physics going as e^-PVED/kT where e is the Euler's number, k is Boltzmann's constant, T is the temperature in Kelvin). The difference in energy from the PVED can be theoretically calculated from a Hamiltonian operator that is scaled by the Fermi electroweak coupling constant. The energy difference between chiral configurations is predicted to be small, around 10^-14 Joules per mol which means that not only is this energy difference believed to be minimally important to early life's synthesis, but it is also out of reach of current experimental techniques. However, it turns out that the PVED predicts that the left handed chiral states would be of lower energy, just as they are found dominantly in life on Earth. The weakforce influences chemical reactions because during beta decay, spin polarized electrons produce a an abundance of left-circularly polarized gamma-rays which, if present during the synthesis of biomolecules would tend to create an enantiomeric excess of left handed molecules. However, laboratory experiments have not shown conclusively that this effect is strong enough to matter either. There is some debate as to the exact nature of the PVED which will depend on further experimental measurements. The weakforce seems to preselect a hand in nature, but it is a feeble force.
Polarization. Optically active organic molecules being synthesized in the presence of polarized light will be chiral. Sunlight is slightly polarized just before sunrise and after sunset. This averages out to zero, but chemical activity that dominates in the morning/evening or occurs in the presence of shadows could feel a net polarization effect. Also plausible are astronomical sources of polarized light outside the solar system. Supernovae have been known to emit circularly polarized light as have star forming or nebulae regions. These sources while weak would create conditions necessary for the synthesis of homochiral biomolecules.
Vorticity. A chemical solution being stirred or agitated results in the synthesis of homochiral biomolecules, however, the handedness of the chirality is random. Certaintly there were chaotic turbulent conditions on the early Earth.

There is no conclusion to be drawn as to how life became homochiral. I found more questions than answers. So I asked Robert Compton for some answers.

1) Enantiomers are allotropes then?

Interesting question but allotropes are "two or more existing forms of an element" such as graphite, diamond and fullerenes. There are a number of fullerenes which are chiral, e.g. C84. The C84 molecule has an R and and S enantiomer as well as the meso- form (the meso is a combination of the R- and S- form). This is illustrated below. One goes from the left to the right by rotating two of the carbons twice and reconnecting the dots going through the achiral meso-form.

2) Life on earth is overwhelmingly 'left-handed' homochiral. Is this merely a coincidence of history? Do you think a fundamental effect like PVED or an environmental effect like polarized light from a local supernova or nebula was responsible for primordial chirality on Earth?

This is the 64 million dollar question. Did life end up as “left-handed” (or better L-amino acids) due to some fundamental bias or was it pure chance and there may be a planet out there that is made up of D-amino acids. I have discussed the possibilites in my review article on “Chirality of Biomolecules” but to summarize it may be due to 1) the influence of circularly-polarized light on biomolecules giving rise to life over long periods of time, or 2)the chiral weak force making one enantiomer be lower in energy than the other ( this is certainty true but the effect is really, really small) or 3) chiral beta – rays interacting with matter to produce handed biomolecules. At the present time I favor the interaction of circularly polarized light on molecules in interstellar space (maybe chiral microwaves). Meteors then bring these molecules to Earth to begin life forms.

I really feel that PVED is too small. My bet is on circularly polarized light from a local supernova or nebula.

3) Subsequent proteins formed in the presence of a particular enantiomer protein will be preferentially homochial to that primordial protein. Assuming 'the spark of life' only occurred once with a particular enantiomer protein present, would you agree that it isn't surprising that life is homochiral? Is this assumption realistic?

Homochirality is understandable. Everyone agrees that life molecules are preordained to be homochiral. But there is no reason that they will be of only one handedness, of a specific chirality. That’s the rub. It has always been a big surprise to me that ALL life is made of L-amino acids ( and chiral sugars in the backbone of the DNA).

4) Imagine we went to planet X and found the same flora and fauna as Earth, but planet X's organisms were dominated by the opposite chiral form as that found on Earth. Could we mate with or consume nutrients from creatures on this planet?

No. I don’t think I would like to try this.

5) It is obvious in biology that chirality is a function of emergent complexity in the system. In physics chirality is often considered to be a function of the deepest laws of nature. Could chirality in physics also be a function of emergent complexity from unseen laws of nature?

I believe the current view is that the Universe began as both matter and anti-matter but bifurcated into matter due to some fundamental reason. Thus the Weak force gives rise to left spinning beta particles. There are a lot of scientists trying to understand how the Universe ended up as matter. This may be the “emergent complexity from unseen laws of nature” that you asked about.

6) In biology and chemistry symmetry breaking on macro scales is understood through chiral selection processes which act on micro scales. That symmetry breaking on micro scales may be traced back to an asymmetry in fundamental physics. Is the universe fundamentally asymmetric?

I think this is ture. You may have seen the book “The Left Hand of Creation” by Barrow and Silk or “The New Ambidextrous Univesre” by Martin Gardner. They touch on this subject. Gardner is fun reading and can be (should be) read by high school students.

Robert N. Compton, Richard M. Pagni, & Volume 48, 2002, Pages 219-261 (2002). The chirality of biomolecules Advances In Atomic, Molecular, and Optical Physics, 48, 219-261

Our Terraqueous globe

2011-01-15T16:18:00.000-08:00

Carl Sagan's Pale Blue Dot is a resonating vision of human's future in space. Sagan combined elements of science, philosophy, and sincere humanity in his public works that has made him a cosmic ambassador. His words seem timeless and in combination with music and visuals his message is even more powerful. Most humans who have ever looked up will enjoy these two videos created by NASA fan Reid Gower, and Sagan fan Michael Marantz.

I was struck by the strange wording that Sagan chooses at the beginning here.

We were hunters and foragers.

The frontier was everywhere.

We were bounded only by the Earth, and the ocean, and the sky. The open road still softly calls.

Our little terraquious globe as the madhouse of those hundred thousand millions of worlds.

Little terraquious globe sounds a little bit like an archaic way of saying pale blue dot. Indeed, I think it is. And the phrase 'the madhouse of those hundred thousand millions of worlds' seems rather forced compared to Sagan's usual poetic ease. I did some searching and found a usage of this term in François-Marie Arouet's (better known by his pen name Voltaire) short story Memnon, the Philosopher of Human Wisdom. The story tells of Memnon who decides to become a philosopher one day and upon that same day he loses his eye, his health, his fortune, and his reason. He passes into sleep in despair at the end of the day and is visited by a celestial spirit in a dream. The spirit says that things could be worse, in fact the spirit states that there are a hundred thousand million worlds and in each world there are degrees of philosophy and enjoyment, but each world has less than the next; there is a world of perfect philosophy and enjoyment somewhere the spirit implies. Memnon is afraid that the Earth must be on the low end of the list and replies, “that our little terraqueous globe here is the madhouse of those hundred thousand millions of worlds”. It is clear to me that Sagan had read this; Sagan's entire attitude to humanity's existence is identical to the thesis of Memnon, the Philosopher of Human Wisdom. Sagan (as does Voltaire in this story) holds that

For All Our Failings, Despite Our Limitations And Fallibilities, We Humans Are Capable Of Greatness.

Thus the great 18th century philosopher Voltaire has profoundly influenced one of the most popular 20th century scientists. Finally, Sagan's work may influence the direction that humanity takes in exploring outer space in the 21st century. I will end this strange tale with the tale itself, Voltaire's short story Memnon, the Philosopher of Human Wisdom.

Memnon one day took it into his head to become a great philosopher. There are few men who have not, at some time or other, conceived the same wild project. Says Memnon to himself, To be a perfect philosopher, and of course to be perfectly happy, I have nothing to do but to divest myself entirely of passions; and nothing is more easy, as everybody knows. In the first place, I will never be in love; for, when I see a beautiful woman, I will say to myself, These cheeks will one day grow wrinkled, these eyes be encircled with vermilion, that bosom become flabby and pendant, that head bald and palsied. Now I have only to consider her at present in imagination, as she will afterwards appear; and certainly a fair face will never turn my head.

In the second place, I will be always temperate. It will be in vain to tempt me with good cheer, with delicious wines, or the charms of society. I will have only to figure to myself the consequences of excess, an aching head, a loathing stomach, the loss of reason, of health, and of time. I will then only eat to supply the waste of nature; my health will be always equal, my ideas pure and luminous. All this is so easy that there is no merit in accomplishing it.

But, says Memnon, I must think a little of how I am to regulate my fortune; why, my desires are moderate, my wealth is securely placed with the Receiver General of the finances of Nineveh: I have where-withal to live independent; and that is the greatest of blessings. I shall never be under the cruel necessity of dancing attendance at court: I will never envy anyone, and nobody will envy me; still, all this is easy. I have friends, continued he, and I will preserve them, for we shall never have any difference; I will never take amiss anything they may say or do; and they will behave in the same way to me. There is no difficulty in all this.

Having thus laid his little plan of philosophy in his closet, Memnon put his head out of the window. He saw two women walking under the plane trees near his house. The one was old, and appeared quite at her ease. The other was young, handsome, and seemingly much agitated: she sighed, she wept, and seemed on that account still more beautiful. Our philosopher was touched, not, to be sure, with the beauty of the lady (he was too much determined not to feel any uneasiness of that kind) but with the distress which he saw her in. He came downstairs and accosted the young Ninevite in the design of consoling her with philosophy. That lovely person related to him, with an air of great simplicity, and in the most affecting manner, the injuries she sustained from an imaginary uncle; with what art he had deprived her of some imaginary property, and of the violence which she pretended to dread from him. “You appear to me,” said she, “a man of such wisdom that if you will condescend to come to my house and examine into my affairs, I am persuaded you will be able to draw me from the cruel embarrassment I am at present involved in.” Memnon did not hesitate to follow her, to examine her affairs philosophically and to give her sound counsel.

The afflicted lady led him into a perfumed chamber, and politely made him sit down with her on a large sofa, where they both placed themselves opposite to each other in the attitude of conversation, their legs crossed; the one eager in telling her story, the other listening with devout attention. The lady spoke with downcast eyes, whence there sometimes fell a tear, and which, as she now and then ventured to raise them, always met those of the sage Memnon. Their discourse was full of tenderness, which redoubled as often as their eyes met. Memnon took her affairs exceedingly to heart, and felt himself every instant more and more inclined to oblige a person so virtuous and so unhappy. By degrees, in the warmth of conversation, they ceased to sit opposite; they drew nearer; their legs were no longer crossed. Memnon counseled her so closely and gave her such tender advices that neither of them could talk any longer of business nor well knew what they were about.

At this interesting moment, as may easily be imagined, who should come in but the uncle; he was armed from head to foot, and the first thing he said was, that he would immediately sacrifice, as was just, the sage Memnon and his niece; the latter, who made her escape, knew that he was well enough disposed to pardon, provided a good round sum were offered to him. Memnon was obliged to purchase his safety with all he had about him. In those days people were happy in getting so easily quit. America was not then discovered, and distressed ladies were not nearly as dangerous as they are now.

Memnon, covered with shame and confusion, got home to his own house; there he found a card inviting him to dinner with some of his intimate friends. If I remain at home alone, said he, I shall have my mind so occupied with this vexatious adventure that I shall not be able to eat a bit, and I shall bring upon myself some disease. It will therefore be prudent in me to go to my intimate friends, and partake with them of a frugal repast. I shall forget in the sweets of their society that folly I have this morning been guilty of. Accordingly, he attends the meeting; he is discovered to be uneasy at something, and he is urged to drink and banish care. A little wine, drunk in moderation, comforts the heart of god and man: so reasons Memnon the philosopher, and he becomes intoxicated. After the repast, play is proposed. A little play with one’s intimate friends is a harmless pastime. He plays and loses all that is in his purse, and four times as much on his word. A dispute arises on some circumstances in the game, and the disputants grow warm: one of his intimate friends throws a dice box at his head, and strikes out one of his eyes. The philosopher Memnon is carried home to his house, drunk and penniless, with the loss of an eye.

He sleeps out his debauch, and when his head has got a little clear, he sends his servant to the Receiver General of the finances of Nineveh to draw a little money to pay his debts of honor to his intimate friends. The servant returns and informs him that the Receiver General had that morning been declared a fraudulent bankrupt and that by this means an hundred families are reduced to poverty and despair. Memnon, almost beside himself, puts a plaster on his eye and a petition in his pocket, and goes to court to solicit justice from the king against the bankrupt. In the saloon he meets a number of ladies all in the highest spirits, and sailing along with hoops four-and-twenty feet in circumference. One of them, who knew him a little, eyed him askance, and cried aloud, “Ah! What a horrid monster!” Another, who was better acquainted with him, thus accosts him, “Good-morrow, Mr. Memnon. I hope you are very well, Mr. Memnon. La, Mr. Memnon, how did you lose your eye?” And, turning upon her heel, she tripped away without waiting an answer. Memnon hid himself in a corner and waited for the moment when he could throw himself at the feet of the monarch. That moment at last arrived. Three times he kissed the earth, and presented his petition. His gracious majesty received him very favorably, and referred the paper to one of his satraps, that he might give him an account of it. The satrap takes Memnon aside and says to him with a haughty air and satirical grin, “Hark ye, you fellow with the one eye, you must be a comical dog indeed, to address yourself to the king rather than to me; and still more so, to dare to demand justice against an honest bankrupt, whom I honor with my protection, and who is nephew to the waiting-maid of my mistress. Proceed no further in this business, my good friend, if you wish to preserve the eye you have left.”

Memnon, having thus in his closet resolved to renounce women, the excesses of the table, play and quarreling, but especially having determined never to go to court, had been in the short space of four- and-twenty hours, duped and robbed by a gentle dame, had got drunk, had gamed, had been engaged in a quarrel, had got his eye knocked out, and had been at court where he was sneered at and insulted.

Petrified with astonishment, and his heart broken with grief, Memnon returns homeward in despair. As he was about to enter his house, he is repulsed by a number of officers who are carrying off his furniture for the benefit of his creditors: he falls down almost lifeless under a plane tree. There he finds the fair dame, of the morning, who was walking with her dear uncle; and both set up a loud laugh on seeing Memnon with his plaster. The night approached, and Memnon made his bed on some straw near the walls of his house. Here the ague seized him, and he fell asleep in one of the fits, when a celestial spirit appeared to him in a dream.

It was all resplendent with light: it had six beautiful wings, but neither feet nor head nor tail, and could be likened to nothing.
“What art thou?” said Memnon.
“Thy good genius,” replied the spirit.
“Restore to me then my eye, my health, my fortune, my reason,” said Memnon; and he related how he had lost them all in one day. “These are adventures which never happen to us in the world we inhabit,” said the spirit.
“And what world do you inhabit?” said the man of affliction.
“My native country,” replied the other, “is five hundred millions of leagues distant from the sun, in a little star near Sirius, which you see from hence.”
“Charming country!” said Memnon. “And are there indeed no jades to dupe a poor devil, no intimate friends that win his money, and knock out an eye for him, no fraudulent bankrupts, no satraps that make a jest of you while they refuse you justice?”
“No,” said the inhabitant of the star, “we have nothing of what you talk of; we are never duped by women, because we have none among us; we never commit excesses at table, because we neither eat nor drink; we have no bankrupts, because with us there is neither silver nor gold; our eyes cannot be knocked out because we have not bodies in the form of yours; and satraps never do us injustice because in our world we are all equal.”
“Pray, my lord,” then said Memnon, “without women and without eating how do you spend your time?”
“In watching,” said the genius, “over the other worlds that are entrusted to us; and I am now come to give you consolation.”
“Alas!” replied Memnon, “why did you not come yesterday to hinder me from committing so many indiscreations?”
“I was with your elder brother Hassan,” said the celestial being. “He is still more to be pitied than you are. His Most Gracious Majesty the Sultan of the Indies, in whose court he has the honor to serve, has caused both his eyes to be put out for some small indiscretion; and he is now in a dungeon, his hands and feet loaded with chains.”
“’Tis a happy thing truly,” said Memnon, “to have a good genius in one’s family, when out of two brothers one is blind of an eye, the other blind of both: one stretched upon straw, the other in a dungeon.”
“Your fate will soon change,” said the animal of the star. “It is true, you will never recover your eye, but, except that, you may be sufficiently happy if you never again take it into your head to be a perfect philosopher.”
“It is then impossible?” said Memnon.
“As impossible as to be perfectly wise, perfectly strong, perfectly powerful, perfectly happy. We ourselves are very far from it. There is a world indeed where all this is possible; but, in the hundred thousand millions of worlds dispersed over the regions of space, everything goes on by degrees. There is less philosophy, and less enjoyment on the second than in the first, less in the third than in the second, and so forth till the last in the scale, where all are completely fools.”
“I am afraid,” said Memnon, “that our little terraqueous globe here is the madhouse of those hundred thousand millions of worlds of which Your Lordship does me the honor to speak.”
“Not quite,” said the spirit, “but very nearly; everything must be in its proper place.”
“But are those poets and philosophers wrong, then, who tell us that everything is for the best?”
“No, they are right, when we consider things in relation to the gradation to the whole universe.”
“Oh! I shall never believe it till I recover my eye again,” said poor Memnon.

American Astronomical Society Meeting

2011-01-13T17:38:00.000-08:00

The 217th American Astronomical Society Meeting was held here in Seattle this week. I attended every session I could, learned many new things, and met or reunited with many astronomy friends. I was too busy to blog during the event, but you can see what I and many others were saying during the conference by searching on twitter for #aas217 and below I have compiled a random selection of abstracts from interesting talks and posters I saw.

The History And Environment Of A Faded Quasar: HST Observations Of Hanny's Voorwerp And IC 2497. Keel, William C. Perhaps the signature discovery of the Galaxy Zoo citizen-science project has been Hanny's Voorwerp, high-ionization cloud extending 45 kpc from the spiral galaxy IC 2497. It must be ionized by a luminous AGN, either deeply obscured or having dimmed dramatically within 200,000 years. We explore this system using HST imaging and spectroscopy. The disk of IC 2497 is warped, with complex dust absorption near the nucleus; the near-IR peak coincides closely with the VLBI core marking the AGN. STIS spectra show the AGN as a low-luminosity LINER, with ionization parameter log U= -3.5, matching its weak X-ray emission. The nucleus is accompanied by an expanding loop of ionized gas 500 pc in diameter, opposite Hanny's Voorwerp. The loop's Doppler span 300 km/s implies kinematic age < 700,000 years. We find no high-ionization gas near the core, further evidence that the AGN is seen at a low radiative output (perhaps now dominated by kinetic energy). [O III] and Ha +[N II] ACS images show fine structure in Hanny's Voorwerp, including limb-brightened sections suggesting modest interaction with a galactic outflow. We identify small regions ionized by recent star formation, unlike the AGN ionization of the overall cloud. These H II regions contain blue continuum objects, consistent with young stellar populations; these occur where projected closest to IC 2497, perhaps meaning that the star formation was triggered by compression from an outflow. The ionization-sensitive [O III]/Ha ratio shows broad bands across the object, and no discernible pattern with emission-line structures or near the prominent "hole" in the ionized gas. These results fit with our picture of an ionization echo from an AGN whose ionizing luminosity has dropped by a factor >100 within the last 200,000 years. Such rapid fluctuations in luminosity could alter our understanding of AGN demographics. Supported by NASA/STScI.

The Discrete X-ray Source Population of M82. Roy E. Kilgard. M82 is the prototypical starburst galaxy in the nearby universe. As such, it is an excellent laboratory for studying high-mass X-ray binaries. We present an initial analysis of the discrete source population of M82, with an emphasis on the ultraluminous X-ray sources, using new and archival observations from the Chandra X-ray Observatory. M82 has been observed for more than 700 ks with ACIS and an additional 190 ks with the HRC, with observations spanning the entire Chandra lifetime to date. These data paint a portrait of the complex spectral and temporal variability of the high-mass X-ray binary population of a starburst galaxy. We will discuss the properties of these sources and the impact they have on the shape of the X-ray luminosity function.
3D Reconstruction of the Density Field: Using Redshift Information in Weak Lensing Analysis. Jake Vander Plas. We present a new method for constructing three-dimensional mass maps from gravitational lensing shear data. We solve the lensing inversion problem using truncation of singular values (within the context of generalized least squares estimation) without a priori assumptions about the statistical nature of the signal. This singular value framework allows a quantitative comparison between different filtering methods: we evaluate our method beside the previously explored Wiener filter approaches. Our method yields near-optimal angular resolution of the lensing reconstruction and allows cluster sized halos to be de-blended robustly. It allows for mass reconstructions which are 2-3 orders-of-magnitude faster than the Wiener filter approach, which will become increasingly important for future large surveys, e.g. LSST. Using this SVD framework, we discuss optimal redshift binning for 3D shear mapping, and explore how this informs the choice of binning in measurements of power spectrum evolution.
Subtraction Of Point Sources From Interferometric Radio Images Through An Algebraic Forward Modeling Scheme. Gianni Bernardi. Cutting edge cosmological investigations of the Epoch of Reionization (EoR) are driving a renovated effort in building low frequency radio interferometers. In order to detect the tiny EoR signal, high dynamic range (DR) imaging at frequencies below 200~MHz is required. High DR images are traditionally obtained by subtraction of bright sources from the ungridded visibilities, however, future generations of large-N radiotelescopes will generate such high volume data stream that the cost of storing the raw ungridded visibilities will be prohibitive. The DR will therefore be limited by well known pixelization effects. Further challenges for an image based deconvolution at low frequencies are a point spread function which varies significantly across the field of view, a time and frequency variable receptor response and ionospheric variability. In this presentation, we introduce a deconvolution algorithm which makes use of forward modeling to mitigate against the limitations of image-based deconvolution. Through forward modeling it is possible to generate a spatially variable point spread function and relate the sky brightness distribution to astrophysical parameters which are then retrieved through a non linear least squares minimization. We applied the method to the deconvolution of point sources on simulated observations of the Murchison Wide-field Array (MWA). MWA is the array with the largest number of correlated elements currently under construction (512 final elements) and will not have the option of storing the raw visibility data over long time integrations. We find that the accuracy to which point sources can be deconvolved/subtracted is only limited by their signal to noise ratio, not by their number or positions, therefore the DR increases with integration time. These results indicate this method to be promising for applications that require high DR imaging, like the detection of the EoR signal. This work was supported by the U.S. National Science Foundation.
Early Astrophysics Results from Planck. Charles R. Lawrence. Since August 2009 Planck has been observing the sky at frequencies from 30 to 857 GHz, measuring not only the cosmic microwave background, but also everything else in the universe that radiates at these frequencies. I will describe the first scientific results from Planck covering a wide range of galactic and extragalactic astrophysics.
Extracting The Astrophysics Of The First Sources From The 21 Cm Global Signal. Jonathan R. Pritchard. Low frequency radio observations of the redshifted 21 cm line of neutral hydrogen have the potential to open a new window into the period from redshift z=6-30 when the first galaxies formed and reionization occurred. Single dipole experiments targeted at the frequency evolution of the 21 cm global signal are likely to provide the first constraints on this epoch. In this talk, I discuss the science of this signal and quantify the prospects for these instruments using a Fisher matrix based approach. I will show that there is considerable room for these simple experiments to constrain the star formation rate and production of X-ray and UV photons by the first luminous sources, provided that issues of calibration, RFI, and the ionosphere can be controlled.
Radio Pulsars as Gravitational Wave Detectors: Recent Observational Results. Paul Demorest. The idea of using an array of millisecond radio pulsars as a nanohertz-frequency gravitational wave detector has continued to attract increasing attention over the past several years. Current experimental sensitivities are beginning to probe the upper limits of the predicted signal strength and a detection seems entirely within reach. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project has been regularly timing a set of 20 millisecond pulsars over the past 5 years. These observations use the two largest radio telescopes on Earth, Arecibo Observatory and the NRAO Green Bank Telescope. In this talk, I will present newly developed analysis procedures and timing results from the NANOGrav 5-year data set. These are then used to place a new experimental limit on the strength of the stochastic nHz-frequency gravitational wave background.
Imaging the Spatial Fluctuations in Cosmic IR Background from Reionization with CIBER. Chris Frazer. The Cosmic Infrared Background Experiment (CIBER) is a rocket-born absolute photometry imaging and spectroscopy experiment optimized to detect unresolved infrared signatures of first-light galaxies that were present during reionization. The signatures from reionization are theorized to be dominant at the wavelengths upon which CIBER surveys. CIBER consists of two wide field imagers to measure the extragalactic background fluctuations in the H and I-Bands (1.6 and 0.9 microns respectively) of the cosmic infrared background (CIB) as well as two spectrometers designed to take measurements of the foreground zodiacal light and the absolute Extragalactic Background Light (EBL) spectrum They imagers are capable of examining high-redshift (z ~ 10-20) CIB fluctuations which will facilitate in the study of surface densities of sources associated with reionization. Studies of galaxies with similar redshift parameters (z > 6) are largely unaccounted for. The spectrometer configuration consists of one low resolution spectrometer and one narrow band spectrometer. They are respectively designed to take measurements of the absolute Extragalactic Background Light (EBL) spectrum, and foreground zodiacal light. In this poster we present the specifications for both CIBER imagers and detail how the fluctuations from galaxies during reionization will be measured.
The 21cm Forest. Katherine J. Mack. Future observations of the 21cm forest -- neutral hydrogen absorption against high-redshift radio sources -- will allow us to trace out the structure of the pre-reionization intergalactic medium (IGM), provided bright radio sources can be found at sufficiently high redshift. I will present a calculation of the expected 21cm forest as might be observed in coming years and show how statistical detection techniques could be used to overcome the low signal-to-noise. I will also discuss the trade-off between the availability of large populations of high-redshift background radio sources and the requirement that the IGM be sufficiently neutral for strong absorption.
Gradual Mode Evolution in PSR B0943+10. Isaac Backus. 40 years after the discovery of pulsars, their emission mechanisms are still poorly understood. A problem which still lacks explanation is that of moding: it is observed that the average pulse profile of many pulsars switches between two or more discrete modes. We present an 8 hr observation of the well known drifting and moding pulsar B0943+10. While the pulsar has two discrete modes of emission, and switches between modes in less than a pulse, there is a gradual evolution of its properties within one of the modes: the linear polarization increases; the drift rate and the average pulse profile change with the same characteristic time. Under the subbeam carousel model, we infer from these dynamics that the ExB drift velocity may gradually vary during one mode which may imply a change in temperature at the polar cap.
Addressing Unconscious Bias: Steps toward an Inclusive Scientific Culture
Author Block. Abigail Stewart. In this talk I will outline the nature of unconscious bias, as it operates to exclude or marginalize some participants in the scientific community. I will show how bias results from non-conscious expectations about certain groups of people, including scientists and astronomers. I will outline scientific research in psychology, sociology and economics that has identified the impact these expectations have on interpersonal judgments that are at the heart of assessment of individuals' qualifications. This research helps us understand not only how bias operates within a single instance of evaluation, but how evaluation bias can accumulate over a career if not checked, creating an appearance of confirmation of biased expectations. Some research has focused on how best to interrupt and mitigate unconscious bias, and many institutions--including the University of Michigan--have identified strategic interventions at key points of institutional decision-making (particularly hiring, annual review, and promotion) that can make a difference. The NSF ADVANCE Institutional Transformation program encouraged institutions to draw on the social science literature to create experimental approaches to addressing unconscious bias. I will outline four approaches to intervention that have arisen through the ADVANCE program: (1) systematic education that increases awareness among decisionmakers of how evaluation bias operates; (2) development of practices that mitigate the operation of bias even when it is out of conscious awareness; (3) creation of institutional policies that routinize and sanction these practices; and (4) holding leaders accountable for these implementation of these new practices and policies. Although I will focus on ways to address unconscious bias within scientific institutions (colleges and universities, laboratories and research centers, etc.), I will close by considering how scientific organizations can address unconscious bias and contribute to creating an inclusive scientific culture.

Winter Solstice Lunar Eclipse Tonight

2010-12-20T12:31:00.000-08:00

As a young child I remember going outside in my pajamas on a cool evening to see a lunar eclipse. Interesting I thought that the moon disappears regularly, yet this event was clearly special. I have since always wished I could have lived thousands of years ago and been able to predict lunar eclipses.

The moon appears to phase in and out of darkness to an Earth bound observer on a monthly cycle, but in reality the Sun's rays are always falling upon the moon. The arced and crescent moon shapes are due to our perspective on Earth of the spherical moon being illuminated from a single direction. The rotation of the moon and the revolution of the moon are synchronously locked in a period of 27 days, 7 hours, and 43 minutes such that only one lunar hemisphere is ever visible from Earth and the other side is apparently locked in darkness. In reality the dark side of the moon sees just as much Sun as the near side on a lunar day cycle almost matching the revolution period. Despite the moon's serene appearance it is a place of extremes because without an atmosphere the Sun heats the moon to 250 Fahrenheit (123 Celsius) during its day and the moon cools to -390 Fahrenheit (-233 Celsius) during its night.

There is of course one time in which the Sun's rays are not falling upon the moon. During a total lunar eclipse the Earth blocks the light from the Sun and the Earth's shadow casts the moon into a dark red copper shadow. A total lunar eclipse will be viewable tonight in the Northern Hemisphere at U.T. 7:41 (or E.S.T. 2:41 am or P.S.T. 11:41 pm). NASA has some further information about the lunar eclipse here. Unfortunately, clouds may block your view so check the weather, indeed here in Seattle the weather may completely block this rare winter solstice lunar eclipse. That is right, this lunar eclipse occurs on the winter solstice. This really is a rare event!

As solace I have looked up several times recently in Seattle to see a moon dog or a moon ring. A moon dog and moon ring is a halo (the ring) and bright spots (the dog) to the left and right of the moon created by the moon's light refracting through ice crystals or high clouds in the atmosphere. Even if you can't see the Eclipse tonight look up this winter to perhaps see the Moon's winter halo.

Supermassive Black Holes

2010-12-16T17:54:00.000-08:00

A black hole is a massive object with such powerful gravity that not even light may escape from it. Black holes only have three unique properties which are mass, charge, and spin. At one time black holes were a speculative phenomena, but astronomers now understand that black holes are a relatively common and important occurrence in our Universe, unfortunately the public and science fiction still seems to be in dark. There are a lot of misconceptions about black holes:

If the Sun was replaced by an equal mass black hole then the Earth would fall into it. In reality we would continue to orbit about the center of mass of the new black hole object and about eight minutes later after the Sun was removed it would be dark on Earth (that is how long it takes light from the sun to get to us).
Supermassive black holes distort the space time around them in a very extreme way. Actually, the larger the black hole the smaller the distortion and tidal forces around it such that a very massive black hole hardly distorts the space time outside its event horizon, of course, every black holes does very strange things with space time inside the event horizon.
Tiny black holes created by particle accelerators like the LHC may destroy Earth. The truth is that these tiny black holes would evaporate extremely rapidly via Hawking Radiation and they have such a small gravitational interaction they would not pull in any other matter.
Black holes lead to extra dimensions. Why don't you jump into one and tell astrophysicists what you find?

Black holes are strange objects. Massive black holes shape the evolution of galaxies, charged black holes are thought not to exist, and spinning black holes pull space itself around at close to the speed of light. According to Einstein mass tells space time how to curve and space time tells mass how to curve. So all mass distorts space in a small manner, but black holes create what are known as singularities where the mathematics which describes the curvature of space time breaks down.

You can solve the equations of general relativity and see how black holes arise, but they also arise in the context of standard Newtonian physics. Consider a rocket launching from earth into space. In order for the rocket to free itself from the gravitational pull of Earth it must be moving at the escape velocity (the actual situation is much more complicated than this, but suffice to say it's... complicated). We can find the escape velocity for any object of mass, m, away from a more massive object of mass M by setting the object's kinetic energy, 1/2 m v ², equal to the potential energy of the object in the massive object's gravitational field, GMm/r, where G is Newton's gravitational constant. A terrible thing happens when you consider what happens if the object had a velocity equivalent to the speed of light, c. Suddenly you find there in a mass and radius combination which creates and object so dense from which not even light can escape. The radius to which an object must be compressed to form a black hole is known as the Shwarzchild radius or the event horizon.

Karl Schwarzchild was a German mathematician who was working as an artillery lieutenant during World War I when he was the first person to solve the Einstein field equations. He found a solution corresponding to a physical object with strange properties: apparently matter and energy could enter, but not exit ( again it is actually more complicated as Hawking has taught us, but I digress ). His solution known as the Schwarzschild metric is a rather succinct description of the spacetime around a non-spinning black hole:

The details of this equation aren't important here. I have shown it for two reasons. First, it really is a thing of beauty that some of you will hopefully appreciate. Second, is the realization that as the radius of the object r approaches the Schwarzchild radius r_s the denominator becomes zero and dividing by zero is next to impossible. This is the singularity. The singularity is unavoidable as no mathematical trick or coordinate transformation can rid the Schwarzchild metric of all singularities.

The astronomy of supermassive black holes

Observations of other galaxies, particularly nearby galaxies, reveal compelling evidence that nearly all galaxies have a super massive black hole at their center. The Milky Way has a supermassive black hole at its center known as Sgr A*. How these black holes form is not well understood, but it must have been long ago when the universe was very young such that the black holes had time to grow. They may form from the collapse of some of the first stars created in the Universe known as Pop III stars or they may form from the monolithic collapse of a cold could of gas in the early Universe. Many galaxies emit very high energy radiation from their centers (ultraviolet, X-ray or gamma ray) that is easily explained by a super massive black hole at their center. These galaxies are said to have Active Galactic Nuclei (AGN), but our Milky Way does not emit such high energy radiation. This an interesting and lucky fact that astronomers have explained by noting that if gas is actively falling onto a black hole it forms and accretion disk which heats up to very high temperatures. Thus matter falling into a black hole emits massive amounts of powerful radiation just before it falls into the black hole. Active galactic nuclei are especially correlated with galaxies which have just undergone mergers with other galaxies which are gas rich; the theory, which is backed up by simulations and observations, says that when gas rich galaxies merge gas funnels into the central super massive black holes and induces a period of high luminosity. The black hole at the center of our Milky Way also undergoes periods of gas accretion or luminosity spikes in the X-ray to radio bands. One such event in May of 2003 was a powerful flare seen located just a few milli-arcseconds from the position of Sgr A* which corresponds to less than ten Schwarzschild radii from the black hole position.

Observing supermassive black holes

How do we know that we have really observed black holes not something else? This is a hard question and astronomers may often talk about compact massive objects instead of black holes if they are not certain about a particular object in the sky. In the case of the supermassive black hole at the center or our Milky Way more direct observations are possible. Astronomers have been watching Sgr A* for decades, but only with modern instruments has powerful evidence come to light. Observations of flare events close to the Schwarzschild radius of a suspected black hole like the event described above are one way. Also watching the gravitational influence of the dark object is another:

The movie above was made with high resolution near-infrared observations over many years (in the bottom left corner is the year of the observations) on the 10 meter Keck telescope in Mauna Kea by a group at UCLA led by Andrea Gehez. These stars are right at the center of the Milky Way in the immediate vicinity of Sgr A* and they are moving in a Keplerian orbit around a central mass which is unseen in optical light. The stars are moving at speeds up to 1400 km/s (or 3 million mph) and so using Kepler's laws of motion the central object is estimated to be four million solar masses. The object is also very minute. Given this great mass and small size astrophysicists only have one explanation for the object. In the near future radio astronomers plan to use interferometry to directly image the event horizon of Sgr A*.

An unexpected relationship between black holes and galaxies

We have good reason to believe that nearly all galaxies contain a central supermassive black hole. Furthermore, the mass of the central black hole strongly correlates with the mass, velocity dispersion, and momentum parameter of the corresponding host galaxy. The most interesting relation is that of the central black hole mass with the velocity dispersion of stars in the host galaxy bulge. This is known as the m-σ relation which has a very simple basic scaling:

Thus the mass of the central black hole and the velocity of nearby stars is highly correlated. This is an empirical relation and so the value of 5 here is approximate (for example in the plot below the value is 5.8 and in some previous work was as low as 4). This relation was discovered and reported in the literature in 2000 by two independent groups (Gebhardt et al. and Ferrarese et al.), but astronomers are still seeking a theoretical model able to elucidate the origin for the correlation.

What is so amazing is how strong the correlation is over a range of galaxy and black hole sizes as seen in the log-log plot above from a very recent paper on the archive by Feoli and Mancini which complied data from Hu 2009. Even a hundred million solar mass black hole will not have a significant gravitational effect on the stars in the bulge of a galaxy (the black hole is big, but there are billions of stars and they are far away from the black hole's gravitational force which of course drops as distance^-2) so the m-σ relation is somewhat of a mystery. Likely the current relation is dependent upon the galaxy and black hole co-evolution (as evidenced by the fact that the empirical scaling is only measured for cosmologically very close galaxies). Theorists and rock bands continue to search for a coherent explanation.

Look up and find your local black hole

Lets try and bring black holes back down to Earth by stargazing. The nearest (super massive) black hole is at the center of our Milky Way Galaxy in the constellation Sagittarius. Sagittarius according to Greek mythology is a centaur archer who was shot with a poisoned arrow and in honor he was given a place in the sky in the constellation Sagittarius. The arrow of Sagittarius points towards the bright star Antares in Scorpius, but it also points to the galactic center and the super massive black hole that lies there. A modern interpretation of the constellation is as a teapot which is as I have outlined it here, but I think the image of a centaur shooting an arrow in the heart of our galaxy is much more dramatic.

Image by Stéphane Guisard

Sagittarius is best viewed during summer nights (this paragraph has been kind of western history and northern hemisphere centric, sorry) and can be found between the constellations Ophiuchus and Capricornus near the galactic plane. The actual object that is identified as the super massive black hole at the center of our galaxy is the luminous compact radio object Sagittarius A* (or Sgr A*) which is not visible in the optical spectrum. Another way to identify Sgr A* is that Scorpius almost wraps his tail around it. Look for Saggitarius's arrow and Scorpius's tail and you will have found a super massive black hole; happy sky hunting.

Gebhardt, K., Bender, R., Bower, G., Dressler, A., Faber, S., Filippenko, A., Green, R., Grillmair, C., Ho, L., Kormendy, J., Lauer, T., Magorrian, J., Pinkney, J., Richstone, D., & Tremaine, S. (2000). A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion The Astrophysical Journal, 539 (1) DOI: 10.1086/312840

Genzel, R., Schödel, R., Ott, T., Eckart, A., Alexander, T., Lacombe, F., Rouan, D., & Aschenbach, B. (2003). Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre Nature, 425 (6961), 934-937 DOI: 10.1038/nature02065

Ghez, A., Salim, S., Weinberg, N., Lu, J., Do, T., Dunn, J., Matthews, K., Morris, M., Yelda, S., Becklin, E., Kremenek, T., Milosavljevic, M., & Naiman, J. (2008). Measuring Distance and Properties of the Milky Way’s Central Supermassive Black Hole with Stellar Orbits The Astrophysical Journal, 689 (2), 1044-1062 DOI: 10.1086/592738

QR Codes

2010-12-06T21:27:00.000-08:00

Science doesn't stop, but blogging occasionally does. Some good posts are on the way, but for today I have something fun: QR codes. You may recognize them as those little matrix barcodes that carry text, numbers, binary, or URLs that are starting to crop up in the real world in augmented reality or hardlink applications where objects in the physical world get linked to the digital world. If you didn't know already you can use your phone or camera to read these things no matter where you see them. They can carry quite a bit of information and because of fault tolerance and error handling in some cases portions of the QR code can be lost and the data still read. I made a few artistic renditions of a QR code that link to The Astronomist. I removed some of the bits from the center and replaced it with an A and I found I was still able to read them handily with the code scanner on my iPhone so I assume they aren't corrupt. Now I just need to make some stickers out of them or something so the digital and physical world will meet at The Astronomist.

Antimatter trapped

2010-11-18T14:47:00.000-08:00

A Nature letter recently reported on trapping antihydrogen. Researchers at CERN snagged 38 antihydrogen atoms in magnetic trap in what promises to the begining of fruitful research on deep symmetries in nature like charge, parity and time. I wrote up an article discussing the research for Ars Technia (where I am now an occasional contributor in case you hadn't heard) and I figure I should shamelessly self promote. From the article:

Researchers at CERN have created and trapped antihydrogen in an attempt to study the underpinnings of the standard model of physics. Antihydrogen is made of antiparticles, specifically an antiproton and a positron, instead of the proton and an electron that are present in natural hydrogen. It has the same mass but opposite charge of its normal matter counterparts.

Antimatter has a bad reputation for being dangerous because it annihilates on contact with regular matter, releasing prodigious amounts of energy. However, the clever reader will note that they have not been annihilated by the antimatter produced at CERN. The reality is that if you gathered all of the antimatter CERN has ever created, you wouldn't garner enough energy to power your laptop through reading this article.

The Universe seems to be made of mostly regular matter, so any antimatter encounters matter and is annihilated immediately after it has been created. Production and detection of cold antihydrogen atoms also happened at CERN in 2002, but those were short-lived. The new Nature letter describes how to overcome the difficulty of containing antihydrogen so that it isn't immediately destroyed.

Continue reading CERN snags 38 antihydrogen atoms in magnetic trap.

A possible young black hole

2010-11-15T21:24:00.000-08:00

Thirty years ago a supernova exploded 50 million light years away (right, so it actually exploded 50 million plus thirty years ago if you take into account the space and time like separation from this event) in the grand spiral design galaxy M100. A year ago a paper titled Evidence for a Black Hole Remnant in the Type IIL Supernova 1979C appeared on the astrophysics preprint archive claiming that the continued X-ray emission from the object was consistent with a 5-10 solar mass black hole. Five days ago NASA announced it was going to make an an announcement. Today NASA made a press release claiming that NASA's Chandra satellite had found the youngest black hole ever. It is a beautiful discovery.

Or is it? Lets peer inside to see the inner beauty of this discovery. The original version of the paper was submitted to Astrophysical Journal Letters , but was not accepted and only after a revision was it submitted again this time to Monthly Notices of the Royal Astronomical Society Letters. Today along with the press release a third revision of the paper went up. The excitement really just boils down to the fact that SN1979c has been a remarkably consistent and bright X-ray source for its 30 year lifetime.

The object seems to have been an approximately 20 solar mass star before it collapsed, but the core which really counts when a star collapse was around 3 solar masses. A core that is much larger than 3 solar masses would collapse into a black hole, a core a little less than 3 solar masses would form a neutron star, but there is no way to know the exact size of the progenitor star's core. Previous theories suspected the object was a magnetar or pulsar wherein the super hot dense objected emitted vast amounts of energy as it cooled and hence this induced the X-ray brightness. The new theory posits that the object is an accreting black hole remnant.

But seriously, an announcement of an accoutrement? It is a little sad how this paper hiding in plane sight was overlooked by bloggers and science writers alike. Even blogs, like Bad Astronomy, that normally expose flimsy stories like this have taken it easy. I think all press releases should come with a warning, science in progress.

Milky Way Hides Gamma Ray Lobes

2010-11-10T19:54:00.000-08:00

The Milky Way has some nerve (or after you see the picture you may think, excuse my language, big cojones) for hiding a massive structure that about equals the size of the visible Milky Way. The Fermi gamma ray satellite observed the structure mired in a fog of gamma rays which are pervasive through our sky. Fermi has been making a survey of the complete sky for some time, but only through careful data analysis and removal of diffuse sources were the lobes readily apparent.

Spotting the lobes inside the Milky Way was difficult because from our view within we can't see the forest for the trees, but astrophysics expect that some galaxies have gamma ray lobes and Fermi has spotted such lobe structures like this in other galaxies such as Centarus A. So this result isn't that unexpected, except that it is. These gamma ray lobes are comparable to the entire size of our galaxy and they are just now being seen for the first time.

The structures are orthogonal to the plane of the Milky Way and have distinct edges; they are surprisingly geometrically perfect. They span about 7.5 kiloparsecs (or 25,000 light years). The lobes are composed of gamma rays which are super high energy photons; the photons obtain such high energies by interacting with particles, like free electrons, which are themselves moving close to the speed of light which then interact with the lower energy photons in their vicinity to boost the photons up to gamma ray energies.

The distinct edges of the lobes are indicative of a large and rapid formation event. The structures may have been formed by a massive burst of star formation followed by stellar explosions which seeded the lobes with gas, dust, and hot electrons over millions of years. There is a supper massive black hole at the center of many galaxies, including the Milky Way, which may create high energy lobes, but those lobes would only form when the black hole is actively undergoing accretion of matter. So this may be evidence that the 4 million solar mass black hole at the center of our galaxy underwent an active period where it accreted a large amount of matter and simultaneously released massive jets of energetic particles just a few million years ago.

It is an exciting discovery, but I don't have anything other than a press release to go on as of yet though a paper is accepted for publication in ApJ so more to come.

Very precise pulsar measurements

2010-10-30T19:02:00.000-07:00

A neutron star is made of neutrons, right? Astrophysicists ponder this question and forge theory after theory, but the only thing they conclude with certainty is that a neutron star by any other name would still be made of the densest form of matter know to exist in our Universe. Under certain conditions a star which has exhausted all of its fuel and is sufficiently massive will not be able to support its own weight with pressure support (as in a regular star) or with electron degeneracy support (as in a white dwarf) such that electrons and protons merge to form neutrons because it is a more energetically favorable arrangement of the matter. A neutron star is a sort of massive atomic nucleus, but without charge. The actual composition and detailed properties of neutron star are still theoretically uncertain.
New measurements of the pulsating neutron star and helium-oxygen-carbon white dwarf binary system J1614-2230 reported in a Nature letter are the highest precision determinations of a neutron star's mass to date. The data comes from the massive Green Bank Telescope using the new Green Bank Ultimate Pulsar Processing instrument which accurately records the time of arrival of each radio pulse sent out by the rapidly rotating neutron star (which is a pulsar). The quality of this instrument, having over a tera op of computing power, and the size of the telescope, 100 meters, made this measurement possible. For a quick rundown of this result you can watch these quick movies on the scientific implications and the technology behind the discovery which were created by the NRAO.

The analysis uses a general relativistic effect involving the time delay of light known as the Shapiro delay effect. When a light ray passes a massive object it follows a curved path. General relativity says that curvature of light rays can only take place when the velocity of the propagation of the light rays also varies with position. The Shapiro delay increases the light travel time through the curved space-time near a massive body. The equation to determine the time delay effect is delightfully simple.

The delay depends on the mass, M, of the time delaying body between the source and the observer, the gravitational constant G, the speed of light, c, and the geometry of the system. The geometry is that light has to be passing near the gravitating body before it gets to the observer for the effect to occur at all so the vector that points from the observer to the source, R, and the vector that points from the observer to the gravitating mass are vital. Pulsar J1614-2230 is a nearly edge on, 89 degrees, system meaning that when the white dwarf passes in front of the pulsar during the binary orbit the Shapiro effect will be very strong. I ran a quick calculation of the time delay and found it to be exactly on the order of a few microseconds. The first figure in the paper shows the geometry and the measured effect.

With this data in hand the standard Keplerian orbital parameters are calculated for this clean binary system and the masses of the objects are calculated. The mass of the neutron star was found to be 1.97 +/- 0.04 solar masses which is the most precise measurement of neutron star mass to date. Unfortunately this measurement technique does not provide any information about the radius of the neutron star, but because the mass was so high it already set a limit on the equation of state of the neutron star matter. This means that we can begin to answer what a neutron star is really made of. Different kinds of matter have a different behavior as you add more mass to them which is intuitive if you thought how discrepant with respect to size a planet made out of cotton candy versus rock would be. This result indicates that exotic models of hadronic matter including hyperons, kaon condensates are ruled out. Condensed quark matter is not ruled out, but highly constrained with this data. This is a big deal for particle physicists because this kind of system is an experiment that could never be carried out in a lab, but is necessary to probe fundamental physics.

This cool result on neutron stars glosses over another application of precise pulsar measurements that the authors of this Nature paper regarded as noise. The plot above is very neat and clean, but before the data looks like that a timing analysis must take into account the time delays associated with many more mundane effects. Effects that change the time of arrival of the pulsar include the variations in the Euclidean distance between the Earth and the pulsar resulting from Earth’s orbital motion, the proper motion of the pulsar, and its binary motion, dispersive delays in the interstellar medium, and time dilation of clocks in the observatory and pulsar frames and along the propagation path. The Earth's orbital motion about the solar system barycenter (known as the Roemer delay) is up to 500 seconds and so must be removed from the data. The powerful thing is that the Earth's orbital motion tells us about the mass and orbits of all the bodies in our solar system. A paper published in the Astrophysical Journal states that with ten years of careful observation of 20 pulsars the masses and orbits of solar system bodies could be determined better than with any other method and even undiscovered trans-Neptunian objects could be found.

Precise pulsar measurements are powerful. The first extrasolar planet ever discovered was actually made with pulsar measurements. Pulsars can tell us about the nature of neutron stars, the properties of own solar system, oh and even gravitational waves. If only astronomers had the money to build a pulsar timing array...

References

Demorest PB, Pennucci T, Ransom SM, Roberts MS, & Hessels JW (2010). A two-solar-mass neutron star measured using Shapiro delay. Nature, 467 (7319), 1081-3 PMID: 20981094

D. J. Champion, G. B. Hobbs, R. N. Manchester, R. T. Edwards, D. C. Backer, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, W. Coles, P. B. Demorest, R. D. Ferdman, W. M. Folkner, A. W. Hotan, M. Kramer, A. N. Lommen, D. J. Nice, M. B. Purver, J. M. Sarkissian, I. H. Stairs, W. van Straten, J. P. W. Verbiest, & D. R. B. Yardley (2010). Measuring the mass of solar system planets using pulsar timing ApJ arXiv: 1008.3607v1

White Cosmonaut, Red Cosmonaut

2010-10-19T10:13:00.000-07:00

Check out this lovely art by Jeremy Geddes. He is a Melbourne artist who works with mostly oil paints. His paintings have glowing colors and he has this recurrent cosmonaut theme that vaguely makes them seem relevant. Below are three of my favorite images that I have seen: The White Cosmonaut, The Red Cosmonaut, and Heat Death. Of his cosmonaut series he himself is vague,

I wanted to construct my own reality through my paintings, a quiet melancholic space that operates by it’s own set of underlying rules and runs it’s own oblique narrative. With each successive painting, I try to build the world and uncover it’s form. The cosmonaut paintings are the first step in this.

And on his piece Heat Death he again lets your mind linger on meaning and reasoning,

Hopefully, I communicate everything I want to say through the painting itself. I’m not interested in giving it a didactic final meaning. I just want to spark questions in the viewer.

Artists have the luxury of letting their art speak so that they don't have to. Scientists don't have this luxury and generally must have a didactic (although, not intending to imply moral) explanation of nature; an explanation which may or may not be close to the truth. Science ultimately doesn't self explain its emphases on truth seeking. Truth is like art, sought for its own sake. Oh and please, if someone wants to buy me the Red/White Cosmonaut diptych print feel free.

The Goldilocks Planet

2010-10-16T18:37:00.000-07:00

Once upon a time there was a planet named Earth. It orbited exactly one astronomical unity away from a G2V type star. Billions of years went by and Earth found that it lived right in the habitable zone where liquid water was maintained on it surface and life spontaneously arose. Pretty soon life on Earth became restless, questioned its own existence, and looked for life on Gliese 581. Earthlings found many planets and exclaimed, 'Gliese 581 b is too hot, Gilese 581 c is slightly too hot, Gliese 581 d is slightly too cold, Gliese 581 e is way too hot, Gliese 581 f is too cold, but Gliese 581 g is just right!' so the story goes.

Gliese 581 is an unassuming star: it is relativity close at 20 light years away (the 87^th closest cataloged star to earth), it is only a third the mass of the sun, and it is relativity quiet in terms of stellar activity (which is beneficial for life because flares scorch planets). It is the sixth planet from Gliese 581 denoted merely as g that harbors so much potential. It is not to hot, not too cold, it is just right. It is the Goldilocks planet. Vogt et al. 2010 recently reported on the discovery of this planet which is a 3.1 Earth mass (or larger) planet orbiting in the habitable zone of the M3V type star Gliese 581. The problem is that this planet may not exist.

The Media

I did not immediately discuss Gliese 581 here at The Astronomist because I wanted to read the paper before weighing in. However the authors were compelled to issue a press release about their findings before making their peer reviewed paper available. After I finally looked at the paper I was somewhat disappointed. The whole thing was a science journalism media circus. A selection of some of my favorite excerpts:

“Found: An Earth like Planet, at Last” Time magazine
“The chances of life on this planet are 100 percent,” Steven Vogt
“Could contain more gold than we could ever imagine” PR Fire
"Are the Gliesans going to Hell?" Huffington Post
"An Alderaan Moment: Earth-Like planet disappears" Death+Taxes

Media coverage is a double edged sword for science. Scientists strive to come up with compelling results that often fall flat when presented to the media or public, but other stories make waves disproportionately large relative to their scientific impact. Arguably the discovery of an earth like planet should have been accompanied by a much larger amount of media attention. The misinformation spread about Gliese 581 g is a symptom of the real problem which is the science. This is not a confirmed planet detection, there is no evidence this planet has a hospitable atmosphere anything like Earth, and there is certainly no evidence of life. This wont stop the media from speculating or spreading dangerous misinformation (like the idea we could travel there if we trash Earth). The quote from Steven Vogt is an example of poor journalism where he prefaced the statement by saying, 'my own personal feeling is that the chances of life on this planet are 100 percent,' but the crucial context was thrown away for headlines.

The Science

All the planets around Gliese 581 were discovered using the radial velocity technique. In any gravitationally bound system the bodies orbit their common center of mass. It is a subtle effect in a star-planet system where the central star dominates the mass. The central star will move at a characteristic speed depending on the orbits of the planets around it. The movement of the star is measured through the Doppler shift of the light emitted by the star. Modern instruments are super sensitive to even the smallest movements of stars down to as little as 1 m/s. Observations of the radial velocity of the star over a period of time (usually several years) is analyzed using Fourier analysis. The Fourier analysis identifies periodic signals in the data corresponding to the orbital period of the planet or planets.

The researchers used two data sets spanning almost two decades. Most of the data came from the researcher's own instrument HIRES, and additional data came from a Swiss group with the HARPS instrument. The HIRES data spans a larger time range, but the HARPS data is more precise. This combined data set is how the researchers identified two new planets f and g.

The Problems

A little after this new Goldilocks planet was announced the Swiss group announced that they could find no evidence of Gliese 581 g in their data. Does this mean it doesn't exist? Well this is tricky. A planetary researcher in my department, Rory Barnes, spoke to the New York times before the Swiss group had spoke up and said that the planet looked like the 'real deal'. After the announcement was made I spoke to Barnes again and he said that he would have to hold off further judgment until more information was available.

The onus of proof in science is upon those who make extraordinary claims. Vogt et al. were only able to find this planet by combing the available data sets; they actually state in their paper that they did not detect the planet in either of the data sets independently, only in combination. The damning part of the Swiss groups statement is that they say they have much more data available at this point that Vogt et al. did no have access to during their analysis. When the Swiss team forces planet g to fit their complete data they actually get a negative fit indicating that planet g really isn't there. The thing about this paper that I am least happy with is the quoted false alarm probability. The false alarm probability appears to be 1% based on the figures in the paper (see figure 3 specifically), but in the text it is quoted as ~10^-5. I don't know what is going on.

Then there is their error analysis (warning this is about to get technical feel free to skip this paragraph). Vogt et al. used the peaks in the power spectrum to identify the planets in the system then subtracted off the highest power modes corresponding to the planets they had found. The power spectrum for each planet carried with it a false alarm probability, but once the planet had been subtracted out of the power spectrum its false alarm probability was washed away (you can see this happening in figure 3). They compound their errors after the 1st, 2nd, 3rd, 4th, and 5th planets which have varying false alarm rates. The proper way to do this is a joint fit model to all planets in the system using Bayesian analysis.

The strangest thing about all this is that when this paper was first submitted to The Astrophysical Journal the Swiss group was reviewing the paper and it was rejected. This Vogt paper meta chronicles its own history and discusses why it was retracted previously over concern of systematics. Unfortunatly the quality of the paper may not have improved. The Swiss group has actually leveled one specific concern, Vogt used perfectly circular orbits to find planet g, but the evidence shows the orbits are probably slightly elliptical. In fact in 2009 Vogt used elliptical orbits, but in this new paper circular orbits have been adopted. The image above illustrates this and makes a pictorial argument as to how circular vs elliptical orbits could introduce errors.

The discovery of an Earth-like planet seems imminent. I do not know if this is it. I will hold off further judgment until more information was available.

References:

Steven S. Vogt, R. Paul Butler, Eugenio J. Rivera, Nader Haghighipour, Gregory W. Henry, & Michael H. Williamson (2010). The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the
Habitable Zone of the Nearby M3V Star Gliese 581 ApJ accepted : arXiv: 1009.5733v1

Also thanks to Amit and Rory for discussion and figures.

ATLAS Mural

2010-09-24T16:48:00.000-07:00

ATALAS commissioned an impressive mural of their detector that has just been completed. Artist Josef Kristofoletti created the massive mural of the Large Hadron Collider's ATLAS detector on the outside wall of loop point 01. The mural was commissioned by the ATALAS experiment after Kristofoletti first painted a similar, though much smaller, mural on the side of the Redux Contemporary Art Center in Charleston, South Carolina. Kristofoletti found inspiration for the art by merging his enjoyment of classic Italian Renaissance murals and his life long fascination with science. He says that the humongous size of ATALAS and the tiny particles it finds make the Large Hadron Collider fascinating, like an unprecedented modern cathedral of science. The event depicted in the mural shows an actual event recorded by ATALAS of a Z boson decay into two muons.

There are more concept pictures here or finished pictures from CERN here.

Skeptical: Philosophical Umpire

2010-09-22T21:30:00.000-07:00

Making good decisions is complicated. Game theory applies logic and mathematics to determine the optimal course of action for individuals when acting in the presence of other participants. Now, individual actions must take into account logic, morals, and personal preference, but there are general rules or situations in which the optimal course of action is clear. This comic (or infographic?) by SMBC illustrates the application of game theory to a classic problem, the prisoners dilemma, and by extension morality.

The prisoners dilemma is a great way to find your moral compass. We can apply a similar decision matrix as used above to many different kinds of situations, like Pascal's wager, where one attempts to bet on the existence of God. The logic of pascal's wager concludes that one should believe, or at least act as if one believes in God (this result is unsatisfactory to many, but wait I have a response). I was recently considering applying a decision matrix to answer the question, 'Should you believe in science?' There are other ways to phrase the question, like 'Should you be a skeptic?' or 'Should you follow logic?' Decision theory gets tricky here. In order to answer the question I recalled an analogy a professor used in a philosophy class I took long ago. My professor wanted us to consider a philosophical umpire calling a game. The umpire could either state that she was very vigilant such that she, 'calls em as I see em' (admitting fallibility), or the umpire could say that, 'I call them as they are' (denial of fallibility). In the situation before replays I could almost see the umpire taking either stance with reason because they are the final arbiter on the field. In this modern age it is completely untenable for an umpire to state that she calls everything'as they are because replays are available. In life any experience that can be repeated is like a game with replays; an experiment is a game with replays. We all must be like the philosophical umpire and we can reason out how to behave using these ideas.

Below I have made a logic table. On the left vertical axis is the true outcome of an event with respect to how you perceived it and on the top horizontal axis is how you see yourself judging the event. The conclusion of the table is that application of the scientific method is really powerful. Admitting that you make errors in judgement means that you always allow potential for improvements in the future outcomes, but insistence on being right leads you to a false world view. I think that scientists, skeptics, and atheist have essentially the same goal and are all standing in the top right corner there jumping up and down trying to get people to choose to be skeptical.

'calls em as I see em' (skeptic)

'calls em as they are'

right

positive result, skeptic world view, positive future results	positive result, superficially correct world view, positive future results
negative result, skeptic world view, potential for improved future results	negative result, false world view, negative future results

wrong

It almost seem to be a tautology that logic says you should use logic to understand the world. This decision matrix casts doubt on the result of all other decision matrices like Pascal's wager such that we can escape being certain that belief in God is best, but simultaneously this result casts doubt on itself. Paradoxically what this really seems to say is that you should be skeptical about being skeptical.

Magnetic Fields in Cosmology

2010-09-13T15:36:00.000-07:00

The existence of magnetic fields on cosmologically large scales is an unsolved problem in astrophysics. Theory favors a universe that did not begin with any magnetic fields present and classical magnetohydrodynamics restricts the spontaneous emergence of a magnetic state under the influence of ideal forces. In a paper entitled Twisting Space-Time: Relativistic Origin of Seed Magnetic Field and Vorticity appearing Physical Review letters Swadesh Mahajan and Zensho Yoshida propose a universal magnetic field generating effect using ideal special relativistic fluid dynamics. Mahajan and Yoshida's insight was that in describing magnetic fields, which are mathematically equivalent to a vorticity, a careful application of ideal dynamics in the framework of distortions caused by special relativity may result in the spontaneous emergence of a magnetic state in contrast to the previous theoretical result.

Magnetic fields are found to be important in every scale hierarchy of the universe. Most notably detailed images of galaxies paradoxically display regions of chaotic turbulence and beautiful grand coherent designs at once. Thus it is clear that turbulent motion on scales below hundreds of parsecs does not necessarily destroy coherent optical or magnetic features over scales of kiloparsecs. Indeed, magnetic fields are indirectly observed at optical and radio wavelengths by detecting the polarization of the electromagnetic field through the Faraday effect and also by the Zeeman splitting effect. The Faraday effect is the rotation of the linear polarization vector of light which occurs when polarized radiation passes through a magnetized and ionized medium. Radio observations are the most powerful technique and by measuring both the dispersion and polarization rotation the mean of the magnetic field along the line of sight can be measured. Such observations indicate a wide range of magnetic field are present in astrophysics. The image at right below shows the magnetic fields present in M51 which are likely similar in structure and strength to that of the Milky Way.

The total radio continuum emission from the "whirlpool" galaxy M51 (distance estimates range between 13 and 30 million light years) is strongest at the inner edges of the optical spiral arms, probably due to the compression of magnetic fields by density waves. The vectors give the orientations of the regular magnetic fields as derived from the polarized emission. The field lines follow nicely the optical spiral arms. Unexpectedly, strong polarized emission is observed also between the optical arms which indicates the action of a dynamo. This image was observed with the VLA in its most compact configuration at 6cm radio wavelength (broadband continuum). As the VLA cannot detect the diffuse, large-scale radio emission, data from the Effelsberg 100-m telescope in Germany at the same wavelength was added. Investigator(s): Rainer Beck (MPIfR Bonn, Germany), Cathy Horellou (Onsala Space Observatory). Image courtesy of NRAO/AUI

Microguass fields are present in galaxies at scales of a few kiloparsecs and on the much larger scales of megaparsecs ordered fields of perhaps a few orders of magnitude less are present in galaxy clusters. Magnetic fields in astronomy are controlled by induction of partially ionized gas. A common model for creating these magnetic fields is the dynamo effect wherein an electrically conductive fluid accelerated by some kinetic force generates convective motions in the fluid; it is plausible that a turbulent hydromagnetic dynamo of some kind coupled to an inverse cascade of magnetic energy wold give rise to regular galactic magnetic fields. Following the basic dynamo theory magnetic field lines can be simulated for galaxies which are consistent with observations. The dynamo theory is actually a mechanism for maintaining or growing fields rather than creating them, but it is expected that minuscule primordial magnetic field seeds in the early universe of cosmological origin drive the magnetic fields observed today.

The magnetic dynamo and the primordial magnetic seed theories are both unsatisfactory. The model wherein the the large scale magnetic field in galaxies is the result of the twisting of a cosmological magnetic fields by galactic differential rotation is not satisfactory because a primordial field wound up by differential rotation ultimately decays in an effect known as flux expulsion. The primordial seed theory must explain the presence of large magnetic fields in higher redshift objects when the universe was much younger when the fields should not have had sufficient time to grow. Researchers disagree over what initial primordial field strength is necessary to create the magnetic fields seen today; estimates vary from as large as 10^-9 gauss [1] to 10^-30 gauss [2], but either way an alternative model would be welcome.

Mahajan and Yoshida's work was motivated by the search for a universal mechanism for magnetic field generation. They key to creating a magnetic field is the vorticity of an ionized material which is analyzed in this paper with topological constraints. In mathematical terms fundamental cosmology requires a topological constraint on the vorticity of the universe (consider that you wouldn't expect the universe to have a preferred rotation), however this constraint can be broken by the application of special relativity. The problem of magnetic fields lies in the fact that vorticity must vanish for every ideal force such as the entropy conserving thermodynamic forces (this can be proven though the governing Hamiltonian dynamics of an ideal fluid where ultimately Kelvin's circulation theorem shows that if the initial state has no circulation the later sate will also be vorticity-free). Introduction of the Lorentz factor γ=(1-(v/c)²)^-1/2 from special relativity destroys the exactness of the ideal thermodynamic force and allows spontaneous vorticity.

The authors find a new term that provides a magnetic field growing mechanism as long as the kinetic energy is inhomogeneous. The authors mechanism can provide a finite seed for even mildly relativistic flows. They provide an example for very standard parameters (electron density n=10¹⁰ cm³, temperature T= 20 eV and velocity, v, compared to c of v/c=10^-2) and find their relativistic drive mechanism remains dominate over other effects until magnetic fields of 1 gauss or so which is much larger than most magnetic fields ever observed, thus the relativistic drive is the only dominant effect. The relativistic drive mechanism will likely help us understand, among other things, the origin of magnetic fields in astrophysical and cosmic settings.

References:

[1] Beck, R., Brandenburg, A., Moss, D., Shukurov, A., & Sokoloff, D. (1996). GALACTIC MAGNETISM: Recent Developments and Perspectives Annual Review of Astronomy and Astrophysics, 34 (1), 155-206 DOI: 10.1146/annurev.astro.34.1.155

[2] Davis, A., Lilley, M., & Törnkvist, O. (1999). Relaxing the bounds on primordial magnetic seed fields Physical Review D, 60 (2) DOI: 10.1103/PhysRevD.60.021301

[3] Mahajan, S., & Yoshida, Z. (2010). Twisting Space-Time: Relativistic Origin of Seed Magnetic Field and Vorticity Physical Review Letters, 105 (9) DOI: 10.1103/PhysRevLett.105.095005

The Future History of the Universe

2010-09-10T18:57:00.000-07:00

Current observations of our universe indicate that the universe is expanding at an accelerating rate. The expansion of the universe will eventually place all galaxies which are not gravitationally bound to the Milky Way beyond our observable horizon (yet I caution that the notion of a horizon is a subtle point and a source of expanding confusion). Galaxies will cease to be brilliant. The passing of time will see stars exhaust all of their fuel. Stars will cease to shine. Black holes will evaporate due to Hawking radiation dispersing a bath of dull photons into the universe. Black holes will cease to exist. The universe will cool as it expands to a uniformly frigid temperature. Entropy will be maximized. The universe will be cold, dark, and lonely.

The future history of the universe described above is an implicit result of the standard cosmology accepted today. It is an extrapolation of accepted theory into the distant future. There is good reason to be skeptical of extraordinary predictions which is why the big bang and the past expansion history of the universe is the major focus of cosmology and not predicting the future of the universe. We need to know exactly what happened in the past to understand the reasons for the accelerating expansion (what is dark energy?). The current observations and the 'standard cosmology' I speak of are part of what is known in physics as the concordance model of cosmology. Every peer reviewed research paper that discusses the universe has this one sentence in it that goes something like this (taken from generic research paper on cosmology and extragalactic astrophysics):

Throughout this paper we assume a Friedmann-Lemaître-Robertson-Walker metric with a standard cosmology with Ω_M=.3, Ω_Λ=.7, H₀=70 km s^-1Mpc^-1.

Lets break down this generic statement and see what it implies. The Friedmann-Lemaître-Robertson-Walker metric implies we are assuming a universe which is consistent with a homogeneous isotropic expanding universe, the Ω values are dimensionless energy density parameters which quantify the energy contribution from matter (mostly dark matter, denoted M) and dark energy (denoted Λ), and finally the H₀ value is the Hubble parameter in units of kilometers per second per megaparsec which describes how fast, v, an object at a given distance, d, is moving away from us such that H₀=d/v. The statement effectively means that the universe is flat (it is conceivably possible that you could travel a very long way in one direction and end up where you started, like what happens if you travel around the earth, but observations indicate that this is not the case so we conclude the universe has no curvature) and the universe is expanding in such a way that the universe will not collapse back down on itself. Thus our best guess is that the universe will keep expanding forever. The consequence of this, and this is the crux here, is that as time moves forward entropy inexorably increases (this is the second law of thermodynamics) to the point that all ordered processes, complex systems, life and semblance of thought is impossible.

If you lived forever it would be hard to avoid the situation where eventually you and your fellow space travelers were huddled around a few dieing stars in a bland galaxy in an exhausted void. There are small stars which are burning today and will be burning in 100 billion years and more stars will form for a while. But eventually, stars really will shut down and cool. You could try to travel to another galaxy, but that would take a long time (if the distance to our neighbor galaxy Andromeda was held constant it would take about 2.5 million years to travel there at the speed of light), and even then there would be few stars and most problematically most other galaxies would have receded beyond our horizon. Where would you want to head in this barren universe? Recent studies of the entropy of the universe indicate that the majority of the entropy in the universe is actually contributed by super massive black holes. Interestingly gravity is rather unlike most systems in thermodynamics. Generally entropy is increased by say smashing something into many pieces, but for gravity when energy is uniformly distributed gravity is quite low compared to the state where matter has collapsed into stars or to the extreme state of a black hole. There is one more step in producing more entropy which occurs as black holes slowly emit radiation in the form of Hawking radiation. A black hole the mass of the sun would emit Hawking radiation for 2 × 10⁶⁷ years which is much longer than the current age of the universe at 13.7 × 10⁹ years. A super massive black hole of 100 billion solar masses, about the mass of our entire Milky Way galaxy, would emit Hawking radiation for 2 × 10¹⁰⁰years. You could hang out near one of these black holes for a while as a source of energy because the black hole would still be producing entropy. Finally, all the black holes would also evaporate and the universe would consist of a diffuse gas of photons and leptons. Any activity in the universe would be very limited at this point and what did occur would take truly epic time scales.

The concordance cosmology, the theoretical models, and the measured parameters implicitly assume that the end of the universe is cold, dark, and lonely. The universe ending as cold void in which life can no longer be sustained is sometimes known as the Big Chill. At this point there is only speculation, perhaps it is philosophical. The universe may expand again in a secondary inflationary epoch or the vacuum may decay into an even lower energy state. Actually, there are other possible scenarios such as the Big Rip in which dark energy pulls apart the fabric of space through some exponentially increasing expansion. Revisionist history is the best kind of history, so when talking about the future history revisions are always welcome. There may already be information about universe which has been erased that would change our expectations. One example of the universe erasing information is if the radius of curvature of the universe is much greater than the horizon distance then observing this curvature would be like trying perceive the curvature of the earth just by looking at the horizon so as the universe, or earth, expanded observing curvature could more difficult. Paradoxically, conceding that there is information about the universe which has been erased which would indicate an ultimate fate other than the one outlined here also supports the argument that the ultimate fate of the universe is an extremely high entropy state.

Conceding that the universe may not be infinite or that the end is simply cold and lonely is very difficult for some. This theme was explored in Issac Asimov's story The Last Question in my previous post. In this story man ponders how the heat death of the universe can be avoided. Man asks the greatest computer created how the second law of thermodynamics can be reversed. [spoiler alert] After hundreds of billions of years the computer still cannot answer the humans. Ultimately all of humanities mental facilities from the trillions of humans spread throughout the universe merge their minds with this ultimate computer to from a singular unified mental process. The question is asked again and there is still no answer. Time goes on until space and time cease to exist, however the ultimate mind continues to ponder the question in hyperspace and eventually finds an answer. There is no one or no thing left to report the answer to so the mind decides to show the answer by demonstrating the reversal of entropy. The mind spends another eternity determining how to do this and writing a careful program to execute. Upon execution of the program the mind reverses entropy and thus creates the universe anew.

The Last Question

2010-09-06T14:08:00.000-07:00

The last question was asked for the first time, half in jest, on May 21, 2061, at a time when humanity first stepped into the light. The question came about as a result of a five dollar bet over highballs, and it happened this way:

Alexander Adell and Bertram Lupov were two of the faithful attendants of Multivac. As well as any human beings could, they knew what lay behind the cold, clicking, flashing face -- miles and miles of face -- of that giant computer. They had at least a vague notion of the general plan of relays and circuits that had long since grown past the point where any single human could possibly have a firm grasp of the whole.

Continue reading The Last Question by Isaac Asimov or hear it spoken below.

It is interesting to note that different versions of this story I have encountered state the the sun will burn for ten billion years or 20 billion years. The written story above says twenty while the spoken story says ten. I don't know what the original version said (does anyone out there?). Perhaps this reflects our changing understanding of our sun which suggests that ten billion years is more appropriate.

Richest Yet Planetary System Discovered: HD 10180

2010-08-24T22:54:00.000-07:00

The era of complex planetary systems is here. The solar-type star HD 10180 is just 39 parsecs away and hosts at least 5 extrasolar planets; this is the richest planetary system yet discovered. The ESO 3.6 meter telescope in La Silla, Chile made the observations of HD 10180 with the precise High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph for six years to confirm their findings.

Cylons and Smelloscopes: False Positives and False Negatives in the Search for Extraterrestrial Life

2010-08-20T10:35:00.000-07:00

Are there planets outside of our solar system? Is there life on other planets? Is life on other planets like life on Earth? These are questions that astronomers, astrobiologists, chemists, and geologists are trying to answer with current experiments. In order to answer these questions we must observe distant planets and we must determine what life on those planets may be like. Detecting extrasolar planets is tricky enough, but imaging what alien life is like may well be stranger than science fiction. Yesterday evening I attended a lecture sponsored by the Seattle Astronomical Society given by Shawn Domagal-Goldman titled Cylons and Smelloscopes: False Positives and False Negatives in the Search for Extraterrestrial Life. It was an excellent lecture and filled with interesting topics. Shawn touched on the philosophical problem of defining life in the broadest of senses (is Number Six alive?) and he pointed out that the verification of life on distant planets faces technical challenges and basic scientific limitations (a smelloscope sure would help!).

Dimitar Sasselov set off minor shock waves of gossip and rumors in the media and astronomy communities when claimed that the NASA Kepler mission had found 140 Earth-like planets a few weeks ago during a talk he gave at the TED Global 2010 meeting in Oxford. The media thought we had found earth's twin, but astronomers knew that Sasselov had exaggerated the situation. Sasselov had to post a redaction of sorts on the Kepler blog in order to clarify what he said. What he should have said is that the Kepler mission will find and verify the presence of potentially habitable planets and that Kepler currently had 140 candidate extrasolar planets. The candidates are not confirmed and so a pessimistic outcome could be that half of the candidates will be false. The difficulty in finding extrasolar planets or life is fraught with false positive and false negatives. A false positive is a detection that seems like exactly what you were looking for, and maybe it is, but the detection was either bad data or you were looking for the wrong thing. A false negative is a detection which you conclude is not what you were looking for, but either your data was fouled or your detection threshold was too constrictive.

How do we find planets outside of our solar system? There are at least five methods to find planets: Doppler shift, astrometric measurement, transit method, gravitational microlensing, and direct detection. Shawn discussed in depth the Kepler mission that is currently monitoring more than 150,000 stars in the direction of the Cygnus constellation for any signs of extrasolar planets that may be orbiting those stars. So, what method does Kepler use to find planets? It watches for eclipses! When a planet orbiting a distant star crosses in front of the star some of the light from the host star is blocked. The planet will transit (astronomers often use the world transit not eclipse for exoplanets) in front of the the star once an orbit and thus the period of orbit can be determined. A secondary eclipse also occurs when the day side of the planet is blocked by the star. The video below illustrates the whole process.

Yes, there are planets outside of our solar system. The current exoplanet detection count is 473 and counting; you can watch that count go up over at Planet Quest. Kepler may double that number, but more importantly it has the ability to find earth size planets. Most of the planets found to date have been large, hot, and inhospitable to most kinds of life anyone can fathom.

How do we detect signs of life on other planets? Astronomers look for bio-markers in the planet's atmosphere. Bio-markers are molecular signatures of certain compounds that could not be produced by non-biological process; bio-markers indicate that dynamic non-equilibrium chemistry is present on the surface of that planet. Astronomers can measure the light emitted as a function of wavelength, the spectra, that a planet emits to determine the molecular species present in the atmosphere. For example the Earth's atmosphere has the spectral signature of water which means it has conditions in which life as we know it can thrive. If we found an earth size planet that had water in its atmosphere which wasn't too hot we would say we had found a habitable planet. If we found oxygen or ozone (03) in an atmosphere it would almost certainly mean life was present on the planet because 03 is quickly removed from atmospheres through standard geological processes such as oxidation of iron, but it may remain present in an atmosphere if it is continually replenished by the photosynthesis mechanism of algae and plants. One of the topics Shawn talked about in his talk and a focus of his research was the problem of being certain that non-biological processes are not creating the oxygen rich atmospheres. The runaway greenhouse effect combined with the photo-disassociation of carbon dioxide can produce oxygen in a similar way to biological life. This is where the smelloscope would be useful: ozone along with other non-equilibrium species such as nitrous oxide and methane in specific ratios would be the scent we are looking for. Bio-signatures were not present on the early Earth. In fact the Earth probably looked a lot more like Venus. The diagram above shows that Venus, Earth, and Mars all have distinct spectral features that tell us about their atmospheres. The hardest part of looking for bio-signatures is that we do not have a telescope that is sensitive enough. Trying to take the spectra of a planet orbiting a bright star is like trying to tell the color of the wings on a gnat hovering around a spotlight on the moon. Like a baseball player holding up one hand to block the sun from his eyes as he focuses on the ball an occulter or star shade working with an existing telescope in space would do the trick. The current funding situation in astronomy is dire, but there is hope that a mission called New Worlds will one day work with the James Webb Space Telescope to allow us to take a closer look at planets which Kepler is finding.

Is there life on other planets? We don't know and it may be a more complicated question than is suspected. There is a bias towards looking for life that is similar to what life on Earth is like. There is a bias towards looking for life that alters its host planet's atmosphere significantly enough to detect it with telescopes on earth. There is a bias towards looking for life that is alive as we define it. These biases may lead to false negatives in the search for life, but as Shawn pointed out the possibilities for life to exist are much grander than our imaginations so we do the best we can. Also, despite the difficulties for finding life on other planets and the gulf between the public's perception of aliens and reality scientists are taking this as a serious venture. Scientists from diverse fields are coming together to forge a path forward. One such project is the Virtual Planet Laboratory which employs scientists in fields such as geology, chemistry, biology, and astronomy. The Virtual Planet Laboratory is a team of scientists who are building computer simulated planets to discover the likely range of planetary environments for planets around other stars so we can better look for habitable planets and distinguish between planets with and without life. However, we can't even discern with certainty the presence of life on Mars or Europa at this point, what hope do we have for finding life on distant planets?

I think there is a lot of hope and I am not alone in that sentiment. I don't search for planets or life in my research, but I think that the search for life, particularly intelligent life, is a fundamental question. It is natural to wonder about the Universe on the grandest of scales, but it is wise to be concerned with what happens on the smallest of scales because that is where we will find life. We expect to find the unexpected in the search for life.

References:

Beichman, C. A., Woolf, N. J., & Lindensmith, C. A. (1999). The Terrestrial Planet Finder (TPF) : a NASA Origins Program to search for habitable planets JPL publication

Limits on Lasers

2010-08-12T23:21:00.000-07:00

Physicists are planning to create a laser so powerful that it will tear apart spacetime, well, it won't destroy spacetime, but it will tear particles out of the vacuum with dire consequences for the laser. I first made the statement that 'lasers will tear apart spacetime' when referring to future ambitious projects planned by the Extreme Light Infrastructure (ELI) when I was writing for Lindau Nature on 50 Years of Lasers. It is a bold claim, perhaps a colorful interpretation of the physics, but none the less recent experimental and theoretical work indicates that there is a fundamental limitation on the attainable intensity of lasers.

The vacuum that makes up spacetime is teeming with virtual particles that are inconsequential to low energy phenomena. Particles and their antiparticles, such as electrons and positrons (e^- and e⁺), can be produced in pairs under certain conditions when energy is converted into matter. When enough energy is focused with laser pulses the peak electromagnetic field strength of the laser is enough to pair produce e^- e⁺ pairs which will cause an avalanche-like quantum electrodynamics (QED) cascade which will instantly disrupt the laser pulse.

A paper recently submitted to the arXiv (this paper hasn't been peer reviewed yet) by A Fedotov, N. Narozhny, G. Mourou, and G. Korn, Limitations on the attainable intensity of high power lasers, outlines how there is critical QED field strength that the authors state is unattainable and it is creeping up on experiments very fast. The idea that lasers could create particles or that there is limit in nature on the magnitude of the electromagnetic field is not new. Neils Bohr first suggested that a maximum field of E_s=2πm²c³/eh was physically unrealizable from theoretical considerations and the vacuum production e^- e⁺ pairs by a massive electromagnetic field was hypothesized in 1950 by J. Shwinger (who later received the Nobel prize for fundamental work in quantum electrodynamics). On the experimental front the limits to the laser was hinted at some time ago. In 1997 the Stanford Linear Accelerator (SLAC) collided what was then the worlds most powerful laser with electrons from the Stanford accelerator. The photons from the laser were boosted to produce backscattering gamma-ray photons which interacted with the oncoming laser beam. The energy of the laser and the gamma-ray photons was so high that real particles of matter and antimatter were created from the vacuum.

In this recent paper the authors argue that simultaneous pulses of lasers could reduce the maximum E_s field that may occur by two orders of magnitude to a mere ~10²⁵W/cm². The new analysis relies on the production of e^- e⁺ pairs at the Shwinger limit, but also takes into account the effect of secondary effects which the SLAC experiment did not have enough energy or speed of pulses to observe. Optimistically the ELI project or the XFEL project could reach the maximum laser intensity within the decade. A super high power facility is planned by the ELI with intensities of ~10²⁹ W/cm² and the European XEFL, pictured above, will create extremely short and intense X-ray laser flashes they may also reach this limit by 2014.

The authors point out that the critical difference with future experiments and previous analysis of electromagnetic field strengths produced by lasers is that the most powerful lasers will play not only the role of the target, but will also be responsible for the acceleration of any new particles created. Thus at high laser intensities electron and positron pairs will be created and will immediately be accelerated to relativistic energies and emit hard photons, which will in turn produce new e^- e⁺ pairs. Thus a back-reaction, an avalanche of new particles, will develop from the vacuum by short focused laser pulses. The authors show that creation of even a single e^- e⁺ pair may result in complete destruction of the laser field.

This year is the 50th anniversary of the first successful laser built by Theodore Maiman and so it is rather fitting that we may have come full circle from the first laser to a theory of the ultimate laser. Yet, hurtles remain in the theory with respect to actually calculating the back-reaction of particles within the laser field (my hunch is that the particle avalanche may act to defocus some energy thus restoring the maximum E_s QED field to a an immense energy...) and in experiment with respect to actually building the ultimate laser.

Thirty Five Images of Space Helmet Reflections

2010-08-12T00:57:00.000-07:00

Cool. Thirty five images of space helmet reflections via 3 Ton Gallery.

Colliding Particles

2010-08-06T14:52:00.000-07:00

Colliding Particles is a series of films following a team of physicists involved in research at the new Large Hadron Collider (LHC). It is a creative documentary series (catch more episodes here) which is really well done and worth watching. Colliding Particles follows Gavin, Jon and Adam and their project, code name Eurostar, in their attempts to find the elusive Higgs Boson. One of the main aims of the the LHC is to discover once and for all whether the Higgs actually exists or not, and ‘Eurostar’ might just hold the key to finding out:

Hubble Bubble

2010-07-29T12:51:00.000-07:00

The Copernican principle holds that humans are not privileged observers of the Universe. Copernicus stated that the Earth is not at the center of the solar system or at any particularly special position in the heavens. Modern cosmology has extended this idea to reason that the earth does not occupy any unique position in the Universe. Modern philosophy of science pushes the principle even further to conclude that every observer (even if they be they little green men) should reason as if they were the most standard observer. However, despite all these humble and rational thoughts it is still tempting to explain certain aspects of modern cosmology that seem finely tuned as consequences of observer selection effects. Namely I am speaking of dark energy or the accelerated cosmological expansion which supposedly could be explained if we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void in mass density. The idea that the region of the cosmos around us could be a void is colloquially known in astronomy as the Hubble bubble. Technically a Hubble bubble is defined as a region of space wherein there is an observed departure of the local value of the Hubble constant from its cosmologically averaged value.

Lets speculate a little further on what it would be like to live in a Hubble bubble. In the standard cosmological model of the Universe the structures we see today like galaxies and clusters of galaxies (and similarly the structures we don't see like the massive dark matter halos the visible matter is embedded in) formed from tiny primordial quantum fluctuations in the early universe. The fluctuations were random variations in density such that locations which were over-dense formed galaxies and those which were under-dense formed voids. It is possible, in fact statistically quite acceptable that there are voids of various sizes in the Universe. These voids would become increasingly under-dense as the Universe evolved and equivalently over-dense regions of the Universe became increasingly over-dense. Inside the void matter would expand outward due to the gravitational pull of matter in surrounding dense regions and thus an observer at the center of the void would see an accelerated expansion of matter outward. Now it is also possible that our entire observable Universe is a Hubble bubble, but that really flies in the face in all of cosmology. It is unfounded, absurd, and really the whole idea of a Hubble bubble may explain dark energy, but is hardly a very good explanation.

The Hubble Bubble is wildly speculative and precision cosmology has almost completely defeated it as a credible explanation. First, as the framework of cosmology has been successful resting on the Copernican principle it seems odd to throw it out now. It is odd and largely misguided. First, the probability of producing a void of necessary magnitude; to mimic aspects of dark energy is extremely small in the standard structure formation models. Second, the probability of an observer being at the center (the only location where the expansion effect would be noticed) is extremely low. Finally, the void would need to be close to spherical to match the observed spatial smoothness (or isotropy) of the universe. These qualitative arguments and many more quantitative arguments from precision cosmology data are laid forth in a recent paper by A. Moss, J. Zibin, and D. Scoot titled Precision Cosmology Defeats Void Models for Acceleration. The abstract follows:

The suggestion that we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y-distortion, and for the first time include the local amplitude of matter fluctuations, σ₈. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an "old age problem", and predict much less local structure than is observed.

The paper makes several quantitative arguments against the plausibility any kind of void model for cosmic acceleration by drawing together an impressive amount of cosmological data and technical expertise, however, they don't ever mention the term Hubble Bubble. A 2007 paper by Conley et al. takes the Hubble Bubble paradigm head on: Is There Evidence for a Hubble Bubble? The Nature of Type Ia Supernova Colors and Dust in External Galaxies. In Conley et al. they explore how dust effects the colors of type Ia supernovae because they reason if the dust can be modeled as a purely local Milky Way effect then the supernovae data would actually favor the Hubble Bubble. Of course, despite difficulties the analysis, they find that in their parametrization there is evidence for more than the simply effect of local Milky Way dust implying doom for the Hubble Bubble. So the Hubble Bubble has been burst.

References:

Adam Moss, James P. Zibin, & Douglas Scott (2010). Precision Cosmology Defeats Void Models for Acceleration arXiv preprint arXiv: 1007.3725v1

Conley, A., Carlberg, R., Guy, J., Howell, D., Jha, S., Riess, A., & Sullivan, M. (2007). Is There Evidence for a Hubble Bubble? The Nature of Type Ia Supernova Colors and Dust in External Galaxies The Astrophysical Journal, 664 (1) DOI: 10.1086/520625

Physics & Music

2010-07-24T17:07:00.000-07:00

I enjoy very much the intersection of classical music and physics (for example see my posts on the phenomena of lightning and on Quantifying Goethe) so if I was in the UK I would definitely be checking out the ongoing performance lecture about the legacy of Albert Einstein the scientist, the man, and the musician. Music was an important part of Einstein's life and his passion for music is what has inspired me to continue to learn the Viola after a fifteen year hiatus. The show is called Einstein's Universe and it is put on by particle physicist Brian Foster and British musician Jack Liebeck. The lecture tour will be a fusion of science communication and classical music. You can read a bit more about the show over at Physics World here and see a video about it below.

You can catch a Foster and Liebeck perform an arrangement of the Mozart violin sonata in C Major k.296 here.

Upper Bound on Neutrino Masses from Galaxy Surveys

2010-07-13T13:48:00.000-07:00

Cosmology not only probes the absolute mass scale of the neutrino but is a completely independent method to test against. In any case, it is imperative to include an accurate prescription for the neutrino in cosmology, as any failure to do so can bias the other cosmological parameters. A cosmological constraint on the sum of the neutrino masses is primarily a constraint on the relic big bang neutrino density Ω_ν. One can relate this density to the sum of the mass eigenstates ∑m_ν as given by Ω_ν= ∑m_ν/(93.14 h² eV). The direct effects of the neutrinos depend on whether they are relativistic or nonrelativistic and the scale under consideration. Neutrinos have a large thermal velocity as a result of their low mass and subsequently erase their own perturbations on scales smaller than the free streaming length. This subsequently contributes to a suppression of the statistical clustering of galaxies over small scales and can be observed in a galaxy survey. The abundance of neutrinos in the Universe can also have a direct effect on the primary CMB anisotropies if nonrelativistic before the time of decoupling (i.e., when sufficiently massive). However, one of the most clear effects at this epoch is a displacement in the time of matter-radiation equality. All these cosmological effects can be used to impose bounds on the neutrino mass. Previous studies have capitalized on these signatures and have started to place sub eV constraints on the absolute mass scale . We utilize the new Sloan Digital Sky Survey MegaZ luminous red galaxy (LRG) DR7 galaxy clustering data to provide the first photometric galaxy clustering constraint on the neutrino and, combining with the CMB, examine the complementarity of these early- and late-time probes. With an almost comprehensive combination of probes this renders one of the tightest constraints on the neutrinos in cosmology and therefore physics.

Cosmological observations provide independent constraints on the neutrino mass scale provided that a few assumptions (a flat universe with Gaussian and adiabatic primordial fluctuations and a constant spectral index for example) can be made. Compared to the prospects of current-to-next generation particle neutrino experiments (like KATRIN) it may be that astronomical surveys of the cosmic microwave background anisotropies or optical surveys of the large scale structure of the Universe will place the tightest constraints on neutrino masses for some time. Continue reading from the excerpt above written by Shaun Thomas, Filipe Abdalla, and Ofer Lahav on their invited viewpoint article in Physical Review Letters (freely available):Upper Bound of 0.28 eV on Neutrino Masses from the Largest Photometric Redshift Survey.

The Size of the Proton Measured with Lasers

2010-07-11T21:37:00.000-07:00

A little over a week ago in Lindau, Germany Theordor Hanch hinted at new measurements of the size of the proton which may impact the fundamental theory of quantum electrodynamics. Hansch's lecture was an overview of the history of lasers progressing from our realization of the wave/particle duality nature of light to new research published in Nature on the size of the proton. The new research relies on the fact that the energy levels allowed within an atom depend upon the quantum mechanical interaction of the proton and the electron (or in the case of this recent experiment the exotic muon particle). Each atom has its own energy levels and corresponding spectral lines like a fingerprint. Understanding the spectra produced by atoms was historically very important, to stress this Hansch called the simple hydrogen spectrum the 'Rosseta stone of atoms.' Tiny discrepancies in the expected spectra of the atom in experiment compared to theory have led to major advances in fundamental knowledge. The breakthrough that allowed for exploration of these discrepancies in the behavior of atoms occurred exactly 50 years ago with the development of the laser.

The Hansch lecture on the heartbeat of light is available to watch on the Lindau conference website here. It is at least worth watching what he explains at minute 18 on the nonlinear self organization of light pulses in pulsed lasers in analogy to mechanical pendulums. He shows a video of ten mechanical pendulums in a row with staggered frequencies ranging from 30 to 39 cycles per minute. Each pendulum corresponds to one of the frequencies present in a laser cavity and at the first moment all the lasers are in phase such that constructive interference occurs corresponding to a laser pulse or a large transfer of energy. Quickly the pendulums get out of phase and although they look chaotic there are smaller emerging and disappearing patterns. If you wait long enough the pendulums briefly line up in phase again and this is when the laser when emit the next big flash of light. This demonstration is lovely because it underlies all of physics, if you are a physicist you probably can immediately visualize what I am describing, if you are not a physicist you may have to see the video to visualize what I am talking about, but everyone will appreciate the beauty of the simple demonstration which was effective enough to illicit a round of applause from the audience.

Historically precision measurement of the hydrogen energy levels were difficult because Doppler broadening is large for the particularly light weight hydrogen atom. Hansch explained that with lasers you can pick out hydrogen that is standing still or at most moving sideways using saturation spectroscopy. The development of lasers allowed physicists for the first time to see single fine structure components in atoms particularity the Lamb shift discerning the 2S state where the electron comes close to the proton and the 2P state where it stays away. The saturation spectroscopy technique allows the Lamb splitting of energy levels to be seen plainly. The Lamb shift depends on the size of the proton, but to probe the proton size more finely tricks are needed.

The notion of size for a particle like the proton that resides in the realm quantum mechanics is tricky to define, but there are two classic ways of measuring its radius: scattering of electrons from a hydrogen atom or by looking at the exact energy levels of a hydrogen atom. The size of the proton has been based mainly on the precision spectroscopy of atomic hydrogen and calculations from bound-state quantum electrodynamics. It is known that a hydrogenic atom with a smaller Bohr radius would enhance the effects related to the finite size of the proton, that is to say a proton interacting with a bound oppositely charged massive particle would demonstrate effects in Lamb shift due to a contribution from the proton's size. A collaborative team of scientists lead by Randalf Pohl have spectroscopically measured the Lamb shift of muonic hydrogen and found the charge radius of the proton is 4% smaller than the previously accepted value.

Muonic hydrogen is like regular hydrogen but the electron has been swapped for a muon. The experiment called for muonic hydrogen in which a muon travels around the proton with a radius 200 times smaller than that of hydrogen constructed from and electron. A muon is an elementary particle similar to the electron, is has the the same negative charge and spin, but it is about 200 times more massive than an electron. The muon 'orbits' so close to the proton in fact that it actually spends some portion of its orbit within the radius of the proton. Muons decay quickly and creating muonic hydrogen is a task that could only be undertaken at the Paul Scherrer institute in Switzerland which is the sole location in the world where a muon beam of sufficient intensity could be generated.

The Lamb shift is the result of angular momentum conservation within the atom. The 2S state of hydrogen has zero angular momentum and the 2P state has an angular momentum of one (don't ask about units). As mentioned earlier the result is that in the 2S state the electron comes close to the proton and in the 2P state it stays away.

The experiment worked as follows. The researchers created muonic hydrogen at the Paul Scherrer Institute with equipment constructed especially for the experiment (it took ten years to build). Once the muonic hydrogen is created the researchers shine in a tunable infrared laser with a frequency corresponding to the splitting between the 2S and 2P states. The laser will excite some of the muons from the 2S into the 2P state (when the muonic hydrogen is created a tiny fraction of of it is naturally produced in the 2S state), but the muons will quickly decay to the ground state emitting a powerful x-ray in the process. The researchers measured the amount of x-rays emitted at each specific frequency they had their infrared laser tuned to and the exact frequency which generated the most x-ray flux is the Lamb shift measurement they made.

The new measurement is discrepant with previous results, but the team has done such a careful job of measurement, the first results indicating a discrepancy were discovered six years ago but the results were held, that theoreticians are questioning the accuracy of fundamental constants like the Rydberg constant and basic theories of quantum electrodynamics. There is some more discussion and interpretation of the experiment over at Uncertain Principles on how the proton is even smaller than we thought. I think that it is a very cool discovery. Hansch commented on discovery during his lecture with an anecdote about Arthuer Schawlow (who received the 1981 Nobel for his work with laser spectroscopy). Schawlow would ask students in the hallways at Stanford, 'What have you discovered?' and Hansch says the message to students is, 'I am not here to learn something old, I am here to discover something new.'

References:

Pohl R, Antognini A, Nez F, Amaro FD, Biraben F, Cardoso JM, Covita DS, Dax A, Dhawan S, Fernandes LM, Giesen A, Graf T, Hänsch TW, Indelicato P, Julien L, Kao CY, Knowles P, Le Bigot EO, Liu YW, Lopes JA, Ludhova L, Monteiro CM, Mulhauser F, Nebel T, Rabinowitz P, Dos Santos JM, Schaller LA, Schuhmann K, Schwob C, Taqqu D, Veloso JF, & Kottmann F (2010). The size of the proton. Nature, 466 (7303), 213-6 PMID: 20613837

Microwave Sky Seen by Planck

2010-07-05T10:24:00.000-07:00

The first image of the microwave sky was released today by the Planck collaboration. The image is the result of a year of observations from the Planck satellite. How far we have come since the first image of the cosmic microwave background by COBE! The most prominent aspect of the image is the bright band across sky caused by diffuse gas and dust emission from our own Milky Way. Also visible are local clouds of gas, nearby galaxies such as Andromeda, and more distant galaxies which host supermassive black holes in their center. The more subtle variations which will be visible when the foregrounds are removed are tiny temperature fluctuations which carry information about the cosmic microwave background and primordial density fluctuations seeded by the Big Bang. However, scientists are waiting to dive into detailed analysis of the multi-frequency data ranging from 30 GHz to 857 GHz until all of the foregrounds and telescope systematics can be understood. Ultimately the Planck data will give us the most precise constraints humans have ever had on the parameters of our cosmos.

Planck is a major step forward in cosmic microwave background (CMB) observations because it measures polarization of microwave photons. The polarization of photons may carry information about the universe from inflation or when the CMB was generated 400,000 years after the Big Bang. Generally when an electromagnetic wave or photon is incident upon a free electron the scattered photon is polarized perpendicularly to the incident direction. Different regions of the CMB may have a net linear polarization generated when radiation from perpendicular directions in the sky has different intensities. Different directions in the sky have different intensities dependent upon perturbations; there are three kinds of perturbations 1) scalar perturbations due to density fluctuations, 2) vector perturbations due to vorticity (like cosmic strings or defects, although these are not likely to be detected), 3) and tensor perturbations due to gravity waves. The Planck mission will be the first CMB space satellite to measure the as of yet unseen gravity wave or "B-mode" poarlization which will reveal the physics of primordial gravity waves when the Universe was in existence for just 10^-36 seconds.

The History of the Universe

2010-06-30T00:30:00.000-07:00

LINDAU, Germany — John Mather is humble when describing his measurements of the cosmic microwave background radiation despite the fact that Steven Hawking described this measurement as possibly the most important discovery humans have ever made. The cosmic microwave background radiation is the remnant glow of the Big Bang; it is the primary evidence. Mather is careful to place his work in context next to the original work of Penzias and Wilson who made the first measurement of the cosmic microwave background radiation.

The cosmic microwave background (CMB) was first measured by Penzias and Wilson in 1965, but it was predicted decades earlier independently by several astrophysicists. You can read about the journey Penzias and Wilson took to making their discovery in this previous post on pigeon waste, cosmic melodies and noise in scientific communication. Cosmologists were not content with the first tenuous measurement of the 2.7 kelvin background, but they would have to wait until the Cosmic Microwave Background Explorer (COBE) was launched in 1989 to measure the CMB to one part in 100,000 or 30 millionths of a degree difference in temperature. In 2006 John Mather and George Smoot received the Nobel Prize in physics for their discovery of the blackbody form and anisotropy of the CMB. Mather and Smoot's precision measurements indicated that the Big Bang produced radiation that was perfectly consistent with the theoretical predictions for a blackbody and that the anisotropy, or spatial variations, of the relic radiation were extremely miniscule. The observations fit the theory so well that when plotting the data the error bars must be enlarged to make them visible.

Mather told the attendees the entire history of the Universe during a morning lecture. First, there was the Big Bang. Then a brief period of stupendous growth occurred known as inflation. The early Universe was extremely hot and contained simple particles of matter as well as antimatter; the matter and antimatter annihilated upon contact until only one part per billion of of the early universe was antimatter (this is good for us, because we are made of normal matter, but a mystery to cosmologists). Within the first 3 minutes the formation of Helium nuclei had occurred. The Universe remained in a dense fog of mostly free protons, electrons, and Helium nuclei until about 400000 years after the Big Bang. At this point the Universe had cooled enough that electrons could become captured by the free protons and Helium nuclei to form neutral atoms. The photons which up until this point had been scattering off of the free particles suddenly found that they could effectively travel the entire distance of the universe before having another scattering. These photons cooled as they traversed the expanding Universe until they encountered the detectors on COBE.

If Mather is the stoic scientist, then Smoot is the adventuring explorer. In a break away afternoon session Smoot had the opportunity to tell young scientists a few more details about the CMB and the ramifications. The minor variations in the CMB are quantum fluctuations that were super sized during the period of inflation. Smoot says that our own galaxy was a quantum fluctuation at one time. Through analysis of the CMB with the technique of spherical harmonics Smoot is keen to to stress that the early Universe is extremely linear and that deviations from the known amount of dark matter, dark energy, or age of the universe creatures significant inconsistencies with the data and the theory.

Every galaxy we observe today is related to the small perturbations present in the early Universe. The cold spots in the CMB are slightly denser than the surrounding areas and so as the universe evolved gravity's long range attractive forces meant that over densities were inherently unstable. The over densities grew larger and larger until galaxies, clusters, and super clusters formed. Today, astronomers are measuring the result of this growth of structure through galaxy surveys such as as the Sloan Digital Sky Survey. The observed distribution of galaxies is perfectly consistent with the theories.

Telling the entire history of the Universe must be a humbling job. Astronomers, Mather says, actually have a simple job of describing the universe, galaxies, stars, and places where life may form. Astronomers don't actually have to say how life formed, but there are researchers and Nobel Laureates here at Lindau who are trying to answer that exact question. Mather finished his talk with more questions than answers. How did we get here? Are we alone? What happens next?

The Nobel Laureate Meetings in Lindau

2010-06-17T18:22:00.000-07:00

I have been on blog sabbatical for some time, but I am going to be back in full force in about two weeks blogging from a lake in southern Germany. I have been invited to Lindau Germany to cover the 60th Meeting of Nobel Laureates in about two weeks. You can follow what I have to say along with several other bloggers on the Lindau Blog and you can also submit an original and stimulating question you would like to ask a Nobel Laureate.

One of the goals of the Lindau conference is to facilitate dialogue between Nobel laureates and young scientists. The conference will consist of lectures by the Nobel laureates followed by panel discussions between the young scientists and laureates. There will be an exchange of ideas on basic research as well as applications in fields such as medicine, physics, chemistry and economics. It is great to see this atmosphere of exchange between the various generations and the encouragement to young scientists for the future. Personally, I am very excited to hear the talks and have the opportunity to ask Nobel laureates questions. I could use some recommendations on good questions to ask a Nobel laureate. Some questions I have thought of

What was an assumption you or your field had that has turned out to be completely wrong?
As a young researcher, how can we deal with the reality of daily failures and obstacles?
What kind of fundamental research could lead to unexpected applications in daily life?

So, what would you ask?

Busy

2010-05-12T21:05:00.000-07:00

I am overwhelmingly busy right now. I wont have any time for The Astronomist until the middle of June or so because apparently taking painful qualifying exams builds character. In the meantime here are some diversions...

The Myth of Gravity

here

The Holographic Universe

here

The World Cup

physics of soccer