The Future of Microwave Background Physics

The cosmic microwave background is now fulfilling its promise of determining the basic cosmological parameters describing our Universe. Future study of the microwave background will mostly be directed towards two basic questions: a complete characterization of the initial perturbations, and probes of the nonlinear evolution of structure in the Universe. The basic scientific issues in both of these areas are reviewed here, along with possibilities for addressing them with further microwave background measurements at higher sensitivities and smaller angular scales. The proposed ACT experiment, which will map 200 square degrees of sky at arcminute resolution and micro-Kelvin sensitivity in three microwave frequency bands, is briefly described as an example of rapidly advancing experimental technique.