The Sciences

WMAP 5-Year Results Released

Cosmic VarianceBy Sean CarrollMar 5, 2008 9:54 PM


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It doesn't seem like all that long ago that we were enthusing about the results from the first three years of data from the Wilkinson Microwave Anisotropy Probe satellite. Now the team has put out an impressive series of papers discussing the results of the first five years of data. Here is what the CMB looks like, with galaxy and foregrounds and monopole and dipole subtracted, from Ned Wright's Cosmology Tutorial:

And here is one version of the angular power spectrum, taken from the Dunkley et al. paper. I like this one because it shows the individual points that get binned to create the spectrum you usually see. (Click for larger version.)

The headline two years ago was "Cosmology Makes Sense." (That was my headline, anyway -- others were not quite as accurate.) This continues to be true -- the biggest piece of news isn't that the results have overturned any foundations, but that the concordance model with dark matter, dark energy, and ordinary matter continues to work. The WMAP folks have produced an elaborate cosmological parameters table that runs the numbers for different sets of assumptions (with and without spatial curvature, running spectral index, etc), and for different sets of data (not just WMAP but also supernovae, lensing, etc). Everything is basically consistent with a flat universe comprised of 72% vacuum energy, 23% dark matter, and 5% ordinary matter. The perturbations are close to scale-free, but still seem to be a little larger on long wavelengths than shorter ones (0.014 < 1-


). Probably the most fun result is that there is, for the first time, evidence from the CMB that neutrinos exist! Good to know. My personal favorite was the constraint in the Komatsu et al. paper on parity-violating birefringence that would rotate CMB polarization. I was in on the ground floor where birefringence is concerned, so I'm sentimentally attached to it. But it's also a signature of some very natural quintessence models, so this helps constrain the physics of dark energy as well. Congratulations to the WMAP team, who have done a great job in establishing some of the pillars of contemporary cosmology -- it's historic stuff.

< 0.067 at 95% confidence

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