Cosmology Solved? Maybe

For two decades the hot big-bang model as been referred to as the standard cosmology – and for good reason. For just as long cosmologists have known that there are fundamental questions that are not answered by the standard cosmology and point to a grander theory. The best candidate for that grander theory is inflation + cold dark matter; it can extend our understanding of the Universe back to 10 sec. There is now prima facie evidence that supports the two basic tenets of this new paradigm: flat Universe and scale-invariant spectrum of Gaussian density perturbations. An avalanche of high-quality cosmological observations will soon make this case stronger or will break it. If inflation + cold dark matter is correct, then there are new, fundamental questions to be answered, most notably the nature of the dark energy that seems to account for 60% of the critical density and how inflation fits into a unified theory of the forces and particles. These are exciting times in cosmology! 1. 1998, A Memorable Year for Cosmology The birth of the hot big-bang model dates back to the work of Gamow and his collaborators in the 1940s. The emergence of the hot big-bang as the standard cosmology began in the late 1960s, with the discovery of the microwave background radiation, the establishment of its black-body spectrum, and the success of big-bang nucleosynthesis. By the 1970s, the hot big-bang was being referred to as the standard cosmology. Today, it is well established and provides an accounting of the Universe from a fraction of a second after the beginning when