Most of cosmology can be captured in a few parameters, but those parameters are themselves mysterious, as I discussed in my previous column (see Physics Today, July 2003, page 10). Now I’ll survey some prospects for understanding them better.
A big reason for excitement and optimism among physicists is the emerging possibility of forging links between fundamental physics and cosmology through models of inflation. Several assumptions in our cosmological models, specifically uniformity, spatial flatness, and the Harrison-Zeldovich spectrum, were originally suggested on grounds of simplicity, expediency, or aesthetics. They can be supplanted with a single dynamical hypothesis: that very early in its history, the universe underwent a period of superluminal expansion, or inflation. Such a period could have occurred while a matter field that was excited coherently out of its ground state permeated the universe.
Possibilities of that kind are easy to imagine in models of fundamental physics....
