- A theory according to which the universe underwent extremely rapid expansion after an original event called the big bang, and has been expanding ever since. The basic homogeneity in the distribution of matter in the universe was established as a consequence of the first phase of inflation. Compare steady state theory. See more at big bang.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.