All good things come from the Cosmic Microwave Background

The CMB evolved into starsAll good things come from the Cosmic Microwave Background. The geometry of universe is defined as flat from studies of the CMB using WMAP. The age of the universe is defined as 13.7 +/- 0.2 billion years from studies of the CMB using WMAP. Even the expansion rate of the universe is defined as 71 +4/-3 km/s/Mpc. Getting to these numbers requires a complicated dance between theory and fact, each trying to mirror the other in every nuance, step and numerical bump and writhe and jive. This tango for truth requires modeling and mathematics and very large expensive computers manned by small flocks of graduate students or post docs. I am not a skilled dancer, and getting at these numbers is the work men and women far wiser than me. I can simple point to the journal articles (start here) and say fine work, and may Planck bring you a new thrill of understanding. (image credit: NASA / WMAP science team)
And, as I stand in awe of the science of WMAP, I also see all the other vast science results that can come out of the CMB. The majority of the results come from simply looking for holes in the constant light of the CMB. For instance, the Sunyaev Zel’dovich effect allows astronomers to find galaxy clusters. As light from the CMB passes through clusters of galaxies, some of the photons interact with high energy electrons – electrons associated with hot gas or accelerated out of some high energy system like a jet. In the interaction, some of the electron and microwave photon exchange energy, and this causes the photon to have a new color (and quite likely a new direction!).
In general, the probability of CMB photons and electrons interacting in any given part of space is very very low (Most of space is empty and lacks electrons the photons can interact with). The only places where there are enough electrons to cause a noticeable number of CMB photons interactions are gas rich, high mass galaxy clusters. By looking for places in the CMB where the distribution of photon colors is a little different, a little higher in energy, astronomers could find galaxy clusters. In reality, astronomers more often look for the Sunyaev Zel’dovich effect where they already see galaxy clusters, and use it to measure the clusters’ densities. It is possible to combine the CMB observations with X-Ray observations, which get at the density of the cluster in a different way, to actually measure the mass and size of distant clusters. One measurement alone isn’t enough, but by studying both X-Ray photons produced by the cluster and the lack of CMB photons (where the “lack of” is also created by the cluster) mass and size can be determined.
Holes and other hills and valleys (more precisely called anisotropies) in the CMB may hide a lot of information. The Oort cloud, which parents long period comets, may also shadow its share of CMB photons. As this cosmic light passes through the cloud of ices and dust, and occasional bona-fide snow balls, some of it scatters. If the Oort cloud is a uniform sphere of snow-like stuff, we may never notice this missing light, but if our solar systems most virgin powder perhaps a bit askew – gravitationally piled up in one place more than another – then will see the 1 part in a lot deviations when we develop better technologies. And with these better technologies, we may also find star formation and dust from AGN.
Every time I read through the titles and abstracts of a new round of papers it seems that something new has been discovered in the light or blocking the light of the CMB. Without this constant light source, science would be far less interesting.


  1. Chris Lintott’s Universe » Blind Light - July 3, 2007

    […] Looking back to the early days of the Universe’s history, we’re like the observers outside the box. The light of the CMB appears to have been emitted from the points where it was scattered in our direction. So just as the edge of Gormley’s box seems to be glowing, so it appears that the Universe of 300,000 years after the Big Bang emitted light which travelled all the way to us today. We see the light as emitted from a surface, like the edge of the box, and we can see all sorts of features in this surface. […]

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