Over the past few years, and especially with WMAP, the CMB data has become the foundation for the standard cosmological model. Any model that purports to explain the birth and evolution of the universe must be able to predict the results in Figure 2. This is a very stringent requirement. The model elements implicit in the figure - superhorizon fluctuations with cosmic structure seeded by a scale invariant spectrum with Gaussian fluctuations in the metric are at the core of our conception of the universe. They are also at the heart of inflation. Indeed, we have started to directly constrain models of inflation (Peiris et al. 2003). This is not to say that our currently favored model is correct. There are elements of the observations, for example the apparent suppression of fluctuations on the largest angular scales, that may call for something beyond the standard model. However, it is truly astounding that we have a model that naturally explains almost all cosmological observations. The model is eminently testable and precise enough to be experimentally challenged. The model is also young enough to admit new discoveries in such areas as dark energy, dark matter, and the birth and growth of cosmic structure.
We have much more to learn from the CMB. To borrow from Winston Churchill, WMAP marks not the end, not even the beginning of the end, but rather the end of the beginning of what we can learn from the CMB. In IAUs ahead we may hope to hear of how observations of the CMB in combination with other cosmic probes determine the mass of the neutrino or the equation of state of the dark energy. Detection of polarization B-modes (See A. Couray, these proceedings) may be be able to tell us the energy scale of inflation. From the ground, new experiments such as ACT, APEX, and SPT are pushing CMB anisotropy measurements to high l and high sensitivity. New experiments such as BICEP, CAPMAP, Polarbear, QUAD, SPORT, are applying new techniques to measure the polarization in the CMB. There is already talk of CMBPOL, a post-Planck satellite dedicated to polarization measurements. No doubt, precise measurements of the CMB will continue to shed light on fundamental physics, cosmology, and astrophysics for years to come.
Acknowledgments
The synopsis above benefitted greatly from discussions with the WMAP team, Dick Bond, Arthur Kosowsky, Uros Seljak and Suzanne Staggs. Figure 4 is from Ned Wright and Figure 6 is from Uros Seljak. We thank Dick Bond and colleagues for sharing their compilation and analysis before publication.