To make my case that twenty years from now cosmologists will refer to 1998 as the year Cosmology was Solved, let me return to my list of necessary elements from the first Section. Here are the explanations according to Inflation + Cold Dark Matter.
Origin of the expansion and definitive measure of the present expansion rate H0 (Hubble's constant). The Universe is still expanding from the inflationary explosion. Thanks to the Hubble Space Telescope's calibration of standard cosmological candles (especially Type Ia supernovae), and techniques based on gravitational lensing and the influence of hot gas in clusters upon the cosmic microwave background radiation, we are zeroing in on the elusive Hubble constant: all current data are consistent with 65 ± 5 km s-1 Mpc-1 (Madore et al. 1998).
Origin of the heat in the Universe and a precise measure of the present temperature of the CMB. The vacuum energy that drove inflation ultimately decays into radiation (heat), and according to inflation, the CMB is the primary fossil of inflation! Thanks to the extraordinary work of John Mather's COBE FIRAS team, the temperature of the CMB has been measured to 4 significant figures, as accurately as the thermometers on the COBE satellite would permit, T0 = 2.728 ± 0.002 K (Fixsen et al. 1996).
Full accounting of matter and energy in the Universe. Inflation predicts that we live in a flat Universe and that the total energy density is equal to the critical density. Observations now provide the following accounting: ordinary matter, 5%; relic elementary particles, 35%; vacuum energy, 60%, for a total summing to 100% of the critical density (see Fig. 3.)
Understanding of the origin of the density inhomogeneities that seeded all the structure seen in the Universe today. They arose from quantum fluctuations on subatomic scales that were stretched to astrophysical size during inflation. The pattern of hot and cold spots on the CMB sky are consistent with this prediction (see Figs. 1 and 5.)
Understanding of the origin of ordinary matter and particle dark matter. The origin of ordinary matter in the Universe traces to a slight excess - part in 1010 of matter over antimatter in the early Universe. As the Universe cooled, all the antimatter annihilated with matter, leaving a tiny bit of matter. Because of the tremendous heat release at the end of inflation, this tiny excess of matter over antimatter must arise after inflation, by interactions among the sea of elementary particles present. A framework for understanding this - called baryogenesis - exists and only the details need to be worked out. The cold dark matter particles remain from the early moments of creation because they are stable and they are ineffective in annihilating with one another.
Understanding of the dynamite behind the big bang. The explosive expansion caused by vacuum energy (or something similar) is the dynamite behind the big bang. Further, in the context of inflationary cosmology, what we previously called ``The Big Bang,'' which was supposed to be the creation of the entire Universe, is demoted to ``our big bang'' and the creation of the large, smooth region of the Universe in which we live. According to Andrei Linde, if inflation occurred one, it occurred an infinite number of times and our bang is but one of an infinite number (Linde 1990).
Understanding of the regularity of the Universe. The portion of the Universe that we see is very regular because it all originated from an extraordinarily tiny portion of the Universe.
Description of the history of the Universe from the big-bang event on. The events after the vacuum energy of inflation is released as heat are as in the standard hot big-bang model.