Archive for random phases

WMAP: The Last Judgement

Posted in The Universe and Stuff with tags , , , , , , on December 21, 2012 by telescoper

It seems the the Wilkinson Microwave Anisotropy Probe, or rather the estimable team of people working on it, have produced yet another set of maps and key results. I believe this will be the final release from WMAP. The paper is on the arXiv here and it represents a synthesis of no less than nine years of measurements of the cosmic microwave background radiation:

Here’s the abstract:

We present the final nine-year maps and basic results from the WMAP mission. We provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate CMB anisotropy from foreground emission, and both types of signals are analyzed in detail. The WMAP mission has resulted in a highly constrained LCDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that Big Bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (3.26+/-0.35). The model fit also implies that the age of the universe is 13.772+/-0.059 Gyr, and the fit Hubble constant is H0 = 69.32+/-0.80 km/s/Mpc. Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity reported earlier by WMAP now has high statistical significance (n_s = 0.9608+/-0.0080); and the universe is close to flat/Euclidean, Omega_k = -0.0027 (+0.0039/-0.0038). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter LCDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness-of-fit, the inflationary flat LCDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology.

The main reason for posting this is to acknowledge the remarkable impact WMAP has had on the field of cosmology. The standard model does indeed account for most available cosmological data extremely well. I’m not entirely sure about the “no significant anomalies” bit in the last sentence, in fact, but I won’t argue with it as it depends entirely upon what you mean by significant. It’s not exactly proven that the fluctuations have “random phases” either. We’ll just have to see whether data from Planck, due to be released next year, will reveal evidence of any physics beyond the standard framework WMAP did so much to establish.