Physics of the Early Universe

Observations of the CMB anisotropy provide more than a snap shot of the matter and energy distribution at about 300,000 years after the initial Big Bang. This snap shot is useful not only because it provides the initial conditions for the Origin of Large Scale Structure but also because it provides information about the processes that produce these "seeds" of large scale structure.

Probe of Inflation and/or Quantum Gravity

In the Big Bang model the Universe has a finite age. The further away in distance, and thus the further back in time, various regions of the Universe are isolated from each other by causality. This is referred to as the horizon problem, since regions (that are separated by distances greater than light can travel since the start of the Big Bang) are not causally connected and therefore cannot be synchronized. It is thus difficult to explain the overall uniformity and homogeneity of the Universe and the existence of the very large scale structures (ripples in the fabric of space-time) discovered by COBE. At present the concept of inflation is the only mechanism that we have that provides a means to explain this phenomena. It is possible that some form of Quantum Gravity with quantum tunneling in the very early epoch (or related mechanism) leads to the accelerating formation of space-time, thus overcoming the standard causality limit.

Test of Cosmological Defects

It is thought that at very early times the fundamental forces were unified. As the Universe expanded and cooled, a series of phase changes (such as steam to water, water to ice) occurred and the forces spontaneously lost their symmetry. Due to the same horizon problem issue of causal connectedness, such a spontaneous symmetry breaking cannot be coordinated in widely separated regions throughout the Universe. As a result, topological defects are generated. These defects have "dimensions" set by the order of the symmetry that are broken: monopoles, strings, domain walls, and textures are examples in order of increasing dimension.

At the moment essentially all classes of defects, except domain walls, have champions advocating that they exist from the GUT (Grand Unified Theory) scale (10¹⁶ GeV) and are the seeds of large scale structure formation, and also account for the observed CMB anisotropies. They do predict a significantly different CMB anisotropy pattern and power spectrum than do the adiabatic perturbations predicted from inflation models. (Adiabatic fluctuations are density variations in all forms of matter and energy that have equal fractional over/under densities).

Cosmic Inflation

Measurement of the Cosmological Constant

Probe of the Nature of Dark Matter

Probe of the Baryonic Content of the Universe