Field of Science

The Cosmos isn't strange, people are strange

The cosmos isn't strange, people are strange. The universe on the largest of scales is actually simple compared to the complexities of the human mind or even the weather. In a statistical sense all current observations indicate that universe is homogeneous and isotropic everywhere. The best evidence for this statement is the cosmic microwave background (CMB) radiation which is light from the big bang that has traveled unimpeded through the universe since recombination. A simple and consistent model for the universe is that just after the big bang an inflationary field with quantum fluctuations rapidly expanded. These fluctuations seeded the CMB with a Gaussian random field of temperature perturbations. The seventh year Wilkinson Microwave Anisotropy Probe (WMAP) data is consistent with an inflationary ΛCDM model that specifies just six parameters (see Larson et al. 2010): the baryon density Ωb, the cold dark matter density Ωc, a cosmological constant ΩΛ, a spectral index of scalar fluctuations ns, the optical depth to reionization τ , and the scalar fluctuation amplitude Δ2R. These results are not new. They are further refinements on previous WMAP data which have all been consistent with the ΛCDM model showing that the universe is flat, with a nearly (but not exactly) scale invariant fluctuation spectrum seeded by quantum flucuations during inflation, with Gaussian random phases, and with statistical isotropy over the entire sky. When WMAP data are combined with additional cosmological data, the ΛCDM model remains robust, and stronger constraints are placed on allowed parameters.

However, if you keep looking closer you can find surprises in the data. The human mind is a readily adept tool at recognizing patterns so a visual inspection of the WMAP image is always a good idea. You can find many statistically unlikely events in the WMAP sky map, but because the human mind is naturally a poor estimator of probabilities strange observations more often only mark the strange patterns of human thought and not fundamental inconsistencies of the cosmos. Exactly what is hidden in the cosmic microwave background is like asking what you see in the clouds, but some claim to see the secret masters of the universe at work. In fact you can see Stephen Hawking's initials in the WMAP image!

Stephen Hawking's initials in the WMAP sky, secret masters of the universe, CMB anomalies
This seems like an outrageous claim so the first thing I did when I heard this was to look at my desktop, which of course is an image of the WMAP sky, and indeed this is no ruse. All I have done in the above image is to outline what was already present; to corroborate this I encourage you to observe the original images of the microwave sky from the WMAP collaboration.

There are many other strange occurrences in the WMAP sky which are not so easily observed by the casual observer or with the human eye. However when you go bowling with the CMB even statistics can lead you astray. You have to ask yourself is physics cognitively biased? Some striking visual anomalies that cosmologists have pointed out include the extremely large cold spot at the center, the four blue ridges in the lower hemisphere, the 'SH' initials, etc. Despite these observations the standard cosmological interpretation (see Komatsu et al. 2010) is, not surprisingly, standard. There are no anomalies to account for, but many researchers are searching for them. The situation is similar to particle physics where if the LHC finds the Higg's boson at the expected energy range then the standard model is validated, but if something unexpected is found new physics, answers to open questions, or a new direction for discovery other than the standard model may be opened (indeed, some find the prospect of merely finding the Higg's boson a disappointment). For example if there is statistically significant support for a hemispherical or dipole power asymmetry across the sky this could point to evidence for a unique inflaton field and, out on a limb here, evidence for physics beyond our universe. The real question is whether or not there are anomolies in the data which are significant. In Bennet et al 2010 the prospect for CMB anomalies is seriously addressed. An excerpt from the abstract
In this paper we examine potential anomalies and present analyses and assessments of their significance. In most cases we find that claimed anomalies depend on posterior selection of some aspect or subset of the data. Compared with sky simulations based on the best fit model, one can select for low probability features of the WMAP data. Low probability features are expected, but it is not usually straightforward to determine whether any particular low probability feature is the result of the a posteriori selection or non-standard cosmology. Hypothesis testing could, of course, always reveal an alternate model that is statistically favored, but there is currently no model that is more compelling. We find that two cold spots on the map are normal CMB fluctuations. We also find that that the amplitude of the quadrupole is well within the expected 95% confidence range and therefore is not anomalously low. We find no significant anomaly with a lack of large angular scale CMB power for the best-fit CDM model. We examine in detail the properties of the power spectrum data with respect to the CDM model and find no significant anomalies. The quadrupole and octupole components of the CMB sky are remarkably aligned, but we find that this is not due to any single map feature; it results from the statistical combination of the full sky anisotropy pattern. It may be due, in part, to chance alignments between the primary and secondary anisotropy, but this only shifts the coincidence from within the last scattering surface to between it and the local matter density distribution. This alignment has been known for years and yet no theory has replaced CDM as more compelling. We examine claims of a hemispherical or dipole power asymmetry across the sky and find that the evidence for these claim is not statistically significant. We confirm the claim of a strong quadrupolar power asymmetry effect, but there is considerable evidence that the effect is not cosmological. The likely explanation is an insufficient handling of beam asymmetries. We conclude that there is no compelling evidence for deviations from the CDM model, which is generally an acceptable statistical fit to WMAP and other cosmological data.
In case no one ever told you, the answer to any question asked in a paper's title is no. So if you make an arbitrary decision on how to run statistical analysis on your data (like something as a trivial as a tuned bin size in a histogram) this imposes a posterior selection on the data which will likely effect your conclusion. In order to draw conclusions about such a complicated observation (I began by saying this was all simple and I maintain that, but the instrument and detectors taking the observations are not simple) you must run Monte Carlo simulations to determine expected deviations from your model. So in conclusion cosmic variance limited data will necessarily show probabilistically unlikely events, and the cosmos isn't strange people are strange. Though this certainly isn't the end of probing the CMB with the PLANCK mission currently flying and CMB polarization just being explored. We still want to know how closely natures matches our theory, exactly or not exactly? And I will give you a hint here, you can always measure again so if you have to ask...

C. L. Bennett, R. S. Hill, G. Hinshaw, D. Larson, K. M. Smith, J. Dunkley, B. Gold, M. Halpern, N. Jarosik, A. Kogut, E. Komatsu, M. Limon, S. S. Meyer, M. R. Nolta, N. Odegard, L. Page, D. N. Spergel, G. S. Tucker, J. L. Weiland, E. Wollack, & E. L. Wright (2010). Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are
There Cosmic Microwave Background Anomalies? ApJ arXiv: 1001.4758v1

1 comment:

  1. Like always, great post. I too found the Bennett WMAP 7 write up on the CMB anomalies interesting.

    "The universe on the largest of scales is actually simple compared to the complexities of the human mind or even the weather."

    Isn't that the truth.


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