theory includes the idea of inflation. In this model, the universe expanded much more rapidly at first, to about 1050 times its original size in the first 10-32 second, then slowed its expansion. The theory was advanced in the 1980s by American cosmologist Alan Guth and elaborated upon by American astronomer Paul Steinhardt, Russian American scientist Andrei Linde, and British astronomer Andreas Albrecht. The inflationary universe theory (see Inflationary Theory) solves a number of problems of cosmology. For example, it shows that the universe now appears close to the type of flat space described by the laws of Euclid's geometry: We see only a tiny region of the original universe, similar to the way we do not notice the curvature of the earth because we see only a small part of it. The inflationary universe also shows why the universe appears so homogeneous. If the universe we observe was inflated from some small, original region, it is not surprising that it appears uniform. Once the expansion of the initial inflationary era ended, the universe continued to expand more slowly. The inflationary model predicts that the universe is on the boundary between being open and closed. If the universe is open, it will keep expanding forever, even though the rate of expansion will gradually slow. If the universe is closed, the expansion of the universe will eventually stop and the universe will begin contracting until it collapses. Whether the universe is open or closed depends on the density, or concentration of mass, in the universe. If the universe is dense enough, it is closed. The universe cooled as it expanded. After about one second, protons formed. In the following few minutesoften referred to as the "first three minutes," combinations of protons and neutrons formed the isotope of hydrogen known as deuterium as well as some of the other light elements, principally helium, as well as some lithium, beryllium, and boron. The study ...
