Inflation.

A short review of inflation is given, starting with a description of the underlying mechanism and the scenario of events. Four variations--old inflation, new inflation, chaotic inflation, and extended inflation--are discussed. It is claimed that the inflationary model provides a plausible explanation for (i) the large number of particles in the universe, (ii) the Hubble expansion, (iii) the large-scale uniformity of the universe, (iv) the nearness of the universe to a critical density, (v) the absence of magnetic monopoles, and (vi) the scale-invariant spectrum of microwave background fluctuations observed by COBE (Cosmic Background Explorer). Finally, it is argued that the plausibility of inflation is enhanced by the fact that inflation is eternal. IMAGES: