Caustics

There are many sublime examples of physics in everyday life that I have come to appreciate. Given that it is summer I will talk about something that you are likely to see, but perhaps you can see it with new light soon.

I am simply going to talk about light rays, shadows, and shimmering in your pool. Watch the video. Notice the brightening of light into little wavering filaments (at about 40 seconds notice the nice filamentary structure of closed loops). The waves in the water's surface are bending the incoming light just like your glasses, a telescope, or a magnifying glass and focusing this diffuse incoming light into the bright areas and lines which you observe. The bright areas shimmer according the to shape of the surface of the water as waves perturb that smooth surface. The pattern of light can then be traced to the waves in the water and then to source of light. In theory there is a direct mathematical mapping to the light rays and the water waves. The places on the lensing plane (in this case the surface of the water) which cause a critical increase in brightness on the imaging plane (in this case the side of a pool) are known as caustics (and would roughly map out the crests of the tiny waves in the pool). In astronomy these shimmering lights rays in a pool are a great analogy for the physics underling some observed phenomena.

Gravitational lenses are a bonanza of science and beautiful images tied together. One of the more famous examples of gravitational lensing is Abell 2218 which is an entire galaxy cluster lensing the background field of galaxies.

At first glance I would not say that the similarities between this image and lights in your pool are particularity striking, but the redeeming factor here is the mathematics. It turns out that the math that describes the critical paths that a given photon will travel from the distant background galaxies through the massive gravitational pull of the foreground lensing cluster uses caustics. Imagine riding a photon from one of the distant galaxies relatively unimpeded until you finally interact with the gravitational field of a cluster of galaxies and then you continue to travel again relatively unimpeded until you are observed as a strongly lensed photon. This is exactly what a photon does as it enters the pool. It starts off at some light source, travels unimpeded, hits the surface of the water where it may be bent to some extreme at a caustic, and then it travels relatively unimpeded again until it is observed.

Large scale structure is another aesthetically pleasing astronomical example that takes cues from the dancing lights in your pool. We can start exploring this strange similarity by looking in a strange place: the millennium run. It is a massive simulation astronomers created to examine the evolution of matter in the universe and the result has a clear visual and physical analogy to the filaments of light seen above. In the image below we see a slice through a three-dimensional dark matter distribution showing the structure of the cosmic-web.

The ripples of dark matter evident in the image were seeded by quantum fluctuations during the period of inflation just after the big bang. These minuscule primordial fluctuations expanded with inflation and continued to grow under the influence of gravity. While galaxies individually remain extremely complex statistically the universe has turned out to be simple and has followed closely to astrophysicist's linear predictions on scales greater than about 100 Mpc (that is a mega parsec which equals 1000 parsecs and that is about 2/3 of the way up our cosmic distance scale). We can examine statistics from our data to show that Fourier components of the density field are random, independent in phase, and are nearly scale invariant in power spectrum just as the theory predicts. If that didn't make any sense, don't worry because all you need to observe is that the theory and simulations display similar patterns to actual data that has been taken of galaxies, such as the image below from SDSS.

This image from the SDSS survey shows the distribution of galaxies we actually observe. Each dot represents a galaxy. Notice that their are voids and over densities in filaments and there is a preferred void and filament size. Galaxies merely cluster and form on top of the gravity dominating scaffold of dark matter; although this image and the millennium run are displaying two fundamentally different types of matter they look similar (and although they seem totally unrelated they also look just like the pool). The physics behind these patterns and the imprints seen in the Cosmic Microwave Background are known as acoustic peaks. They are literally oscillations of energy in the early universe and like an instrument's string that has been plucked the modes which resonate can tell us about the object resonating (also, the astute listener that the music accompaniment to the video is Johann Sebastian Bach's Cello Suite #1 in G major and this is no coincide). This may sound like all smoke and mirrors, but these acoustic peaks have been seen in the 2dFGRS and the SDSS. So if this all went over your head just realize that the striking part of all of this is that the patterns from astronomy match the patterns of light seen in any pool!

There is even more science you can think about in the pool this summer. Notice that the focused light on the sides or bottom of the pool is directly related to the current shape of the water's surface between where the light is being focused and the source of light. The really crazy thing to think about is this: there is roughly a certain size of focused light ray that is most common, meaning there is a certain size of wave disturbance in the pool that is most common, meaning that... Often the light rays form loopy circles of sort, but notice that the loops of light are not several meters in diameter nor are the less than a few centimeters in diameter. Nature has chosen a preferential size scale for these loops of light, just as it has chosen a preferential size scale for galaxy clusters! Why is this? Well, we could go through the looking glass here, but maybe it is time to let you just think it out on your own or relax by the pool.

This is just to say

A poem inspired by William Carlos.

I can not
detect you dark matter
save your influence
on gravity

and neutrinos
I don't care
for the way you pass
through my hands

You and neutrinos
deserve each other
when cosmology ends
keep your secrets

Apollo Landing Sites

As I promised a few weeks ago here are the Lunar Reconnaissance Orbiter's images of the Apollo moon landing sites, here on the NASA mission page. In the future there will be more images with much higher resolution so stay tuned.

These images of relics on the moon remind of us the past history that we have had there (yes, we were really there), but the purpose of the current missions is to scout landing areas looking forward to future missions. However, there are some troubling aspects to the moon endeavor. Michio Kaku points out in this article in Forbes that the economic cost of space exploration has historically been prohibitive. I believe this cost argument is particularly poignant in light of other basic research that is underfunded when space missions indulge in such large portions of research budgets. Yet, there is also the possibility that space/lunar operations could be a multi billion dollar industry, a private industry. The Lunar X Prize will be the first incentive for private companies, but a mere drop in the bucket compared to the flood of investments a successful company could take in. In the future there are several key points to keep in mind that will make space exploration a lasting destination and not a fleeting race.

• Robots: Robots are cheaper, hardier, and more reliable than humans. Any mission that involves humans faces skyrocketing costs and redundant backup life support systems increasing complexity and timescales for viable missions.
  
• Economics: A good program for space must be a profitable program. The government should fund high risk scientific projects and let private industry lead the way in other areas.
  
• Science: Many of NASA's missions don't have clear scientific goals, nor do they objectively analyze their missions in retrospect to determine what scientific goals they have achieved. NASA should examine the work it does on a scientific basis and not merely from their engineering perspective which they have historically done (and historically they have been great engineers). If the space station is a "station to nowhere", will a lunar station be a station nowhere?
  

SpaceX

SpaceX was zero out of three for their commercial rocket launches until last year in September when their Falcon 1 launch vehicle made it to space. It was merely a proof of concept (after they destroyed payloads including at least three satellites for the department of defense and NASA and the ashes of some 200 people everyone thought it would be a good idea not to risk anything valuable). Now they have done it again with an actual satellite on board and the company's future is bright.

This is revolutionary for space flight because of the cost margin advantage SpaceX will offer to those wishing to place things in space. A profitable space company is a step towards a space economy. The owner of SpaceX, Elon Musk, is revolutionizing all modes of transportation with his electric car company, Tesla, which is already producing viable all electric vehicles. Further SpaceX may eventually carry cargo to the International Space Station when the shuttle has retired (read NASA can't cut it in this economy).

Astronomy is Dangerous

Photo by Abulic Monkey on Flikr.

Astronomy is a rather sheltered and tranquil endeavor, unless your telescope spontaneously snaps itself in half and crushes you. I thought the warning sign above was hilarious, but it got me thinking. Astronomy is dangerous. No, seriously astronomy is dangerous. The historical precedents tell a clear story. Long ago emperors and kings would stake their claims on the constancy of the heavens. The rulers employed astronomers (or astrologers, in the past these two professions were not distinguishable, but today their differences could not be more evident. Astronomers are like astrologers they way car is to carpet) to predict such things as the traverse of the Sun each day, the waxing and waning of the Moon, the procession of the constellations with the seasons, eclipses, comets, and supernovae. Astronomers had a good thing going working for kings. Alas, all good things must come to an end. Eclipses, comets, and supernovae sapped the precision prediction power of would be astronomers and the cosmic forecasters paid the price in their blood. In the case of supernovae the astronomers didn't stand a chance. Take for example supernova 1054. Chinese, north American, Persian and Arabic astronomers all observed and recorded it as being bright enough to see in daylight for 23 days and visible 653 nights! All of Europe failed to notice the brightest star in the sky? Perhaps the church saw to it that everyone who saw the star would also see their heads removed from their bodies.
Astronomers are clever in the face of danger and have always gotten the last laugh. Take one last historical anecdote. Galileo was persecuted by the Catholic church for his scientific views, but through cosmic karma Galileo's middle finger (I have seen it with my own eyes at the Museum of History of Science in Florence) has been stickin it to the Vatican for the last three hundred years.

Dinosaurs

Dinosaurs via the New York Times.

Extraterrestrial Imaging

The Lunar Ranger Orbiter did indeed release some images today, but they were just shadows on the moon. These images of Mars geography from Pruned are much cooler:





The maps are from USGS Astrogeology Research Program who also make great things like globes of Mars and Venus which you can construct.

Waiting is the hardest part

The New Horizons craft launching on the most powerful Atlas V rocket ever. Image by Ben Cooper

The New Horizons spacecraft took off in 2006 bound for Pluto. It took nine hours to make it past the moon. It wont arrive at Pluto until 2015. While we are waiting...

The Lunar Reconnaissance Orbiter recently arrived at the moon; it took five days. That is slow, but the good news is that soon I think we may have images of the Apollo moon landing sights. So have excuses ready moon conspiracy enthusiasts. In the mean time, keep waiting...