This rapid expansion blows the Universe up such that light that reaches us from antipodal directions today, comes from regions that have been close together in the early stages of inflation (solution to the horizon problem). By the same mechanism inhomogeneities are stretched out until they become invisible (solution to the flatness problem). Thus, inflation predicts that the Universe is spatially flat. (This statement, and thus the inflationary scenario, can be falsified!)
When the rapid expansion stops, the Universe is cold and empty. All energy is stored in the motion of the scalar field(s) that drive inflation. This energy has to be converted to thermal energy to heat up the Universe. After this stage inflationary cosmology follows the Big Bang model. Any model for inflation that is not able to reach at least energies of about 1 TeV during the heating up is not able to explain the existence of baryons and thus is ruled out.
After the end of inflation fluctuations will cross into the Hubble horizon and form, by the action of gravitational attraction, the structures in the Universe.
Inflation predicts that the spectrum of these fluctuations is almost scale-free at horizon crossing.
Inflation predicts that the spectrum of gravitational waves is almost scale-free at horizon crossing.
If inflation is realized due to the potential energy of a slow rolling scalar field (slow-roll inflation), the amplitude of gravitational waves is small compared to the amplitude of density perturbations.
The density fluctuations and gravitational waves from inflation give rise to anisotropies in the temperature, which first have been seen by the COBE team. (For a nice summary of CMB experiments visit Max Tegmark's CMB data analysis center.) Upcoming satellites (MAP, Planck) will probe the cosmic microwave background with high precision. From these measurements a determination of the cosmological parameters at the few % level will be possible.
For more details have a look at the slides from my colloquium talk The inflationary Universe, that I gave at GSI, Darmstadt in January 1998.
Dominik J. Schwarz
Last modified: December 3, 1999