In everyday life, we use the word "universe" to mean everything that exists. But ideas about how the universe was born suggest that we may need to limit the definition to everything in our "bubble" of spacetime. That's because there may be an infinite number of universes, each with its own beginning and end, its own laws of nature -- and many with their own forms of life.
This idea is known as the multiverse. It came out of research into cosmic inflation -- a brief period before the Big Bang during which the universe expanded at a staggering rate. In recent years, physicists have started to lean toward the idea that this process repeats itself over and over, giving birth to an endless number of individual universes. Steven Weinberg, a Nobel Prize-winning physicist at the University of Texas, explains:
WEINBERG: The original picture of inflation was of a single universe undergoing a period of exponentially rapid expansion, which was then followed by the ordinary expansion of the ordinary Big Bang. But I think opinion has been shifting more and more toward a grander picture in which our inflation followed by our Big Bang has been just one episode in a much larger multiverse with many Big Bangs starting with periods of exponential expansion, inflation, followed by a slower expansion, and that this happens here and there, again and again, time without end.
Script by Damond Benningfield, Copyright 2011