Expert: Courtney Seligman - 7/7/2010

Question
Dear expert,
could the Universe have been beginless, or eternal (thus having actually INFINITE PAST)?
some mathematicians and philosophers oppose this idea because, according to them, an actually infinite quantity of something in the reality leads to logical absurdities.


thank you

Answer
Standard cosmology (the study of the origin and evolution of the Universe) treats the Universe as half-infinite. That is, it has an infinite future, but a finite past (the so-called Big Bang, about 13.7 billion years ago). However, the Universe is believed to have originated from a glitch in the space-time of some previous Universe (see http://cseligman.com/text/prologue.htm for a discussion of this), and if that is correct, the set of universes which includes our own, any previous universes, and any other universes created in a similar way, could conceivably be infinite in every sense. However, there would be no way to observe any of the previous or other universes, as each would exist in a completely separate space-time, so for all practical purposes, "the" universe (meaning ours) is at best half-infinite.

This does not mean that the contents of the Universe are even half-eternal. There are physical theories which suggest that matter may disintegrate and disappear over long time periods. If this is correct, any changes would take place over very long time periods (add about a hundred zeroes to the current age of the Universe), and there has been no verification of the theories so far, so they may be wrong. If so, then both the Universe and its contents could be half-eternal, in the sense of going on into the infinite future. But they would still not be eternal, in the sense of having existed forever, both in the past and in the future.

For a few decades there was a theory of an eternal universe, the so-called Steady State model of the Universe, which proposed that the Universe had an infinite past, as well as an infinite future. That theory made predictions about the nature of the Universe which were soon shown to be wrong, so it was abandoned. But that doesn't mean that some variation on current theory couldn't turn our thinking in another direction. It just isn't very likely that such a theory will be developed or shown to be correct anytime soon.

As far as any opposition due to supposed logical inconsistencies, cosmologists aren't concerned with what someone else might consider reasonable. For them, even the sky is no limit, and any theory would be considered worthy of study, until observations can be made which show that it is wrong.