Because this is a debate, I have been purposefully provocative (as my colleagues can testify, even more so than usual). The scientist in me appreciates that we are still far from ``Cosmology Solved,'' and that the solution may be richer than or even radically different from Inflation + Cold Dark Matter. Big surprises could still be ahead. Still, I think I can see the top of the mountain emerging through the haze.
By any measure, Cosmology is entering a Golden Age, as prophesied by David Schramm. We have a well established foundation in the hot big-bang model; we have bold and expansive theoretical ideas born of the inner space/outer space connection, and now, we are seeing the beginning of an avalanche of high-quality observations that will test these ideas - 1998 was only the tip of the iceberg!
It may well be - and it is certainly my opinion - that 1998 is remembered as the year that Inflation + Cold Dark Matter became a part of the standard cosmology. Or, it may be written that 1998 was zenith for Inflation + Cold Dark Matter, and it was downhill for it thereafter. If the latter proves to be true, armed with an enormous amount of information about the origin and evolution of the Universe and with expectations for learning even more, we will have to go back to the drawing board for new ideas. And there is no doubt that those ideas will have to come from the inner space/outer space interface.
If Inflation + Cold Dark Matter does pass the series of stringent tests that will confront it in the next decade, there will be questions to address and issues to work out. Exactly how does inflation work and fit into the scheme of the unification of the forces and particles? Does the quantum gravity era of cosmology, which occurs before inflation, leave a detectable imprint on the Universe? What is the topology of the Universe? Are there additional spatial dimensions, and if so, how many and how big? Precisely how did the excess of matter over antimatter develop? What happened before inflation? What does Inflation + Cold Dark Matter teach us about the unification of the forces and particles of Nature? And then there is the amazing zoo of objects in the Universe to understand.
I thank the other participants in this Great Debate, for the many conversations, recent and over the years, that have stimulated and helped shape my thinking about the Universe. My work at the boundary of elementary particle physics and cosmology is supported by the Department of Energy (since 1978) and by NASA (since 1983), for which I am very grateful.