Expert: Courtney Seligman - 8/5/2010

Question
Dear expert,


I can't manage to grasp something in what many cosmologists state: according to them, the Universe had a beginning in time and, moreover, time didn't exist "prior" to that beginning.

Because, to me, it's logical that when one says "a thing begins to exist", one necessarly implies a time before the beginning of that thing when the latter didn't exist yet.

Is reasoning is faulty or these cosmologists are contradicting themselves?



                              Thank you.  

Answer
As far as our own space time is concerned, there is a beginning -- a time when there was only a single point of space-time, with nothing before that. This was the instant of the Big Bang (or more accurately, in current Big Bang cosmology, the Inflationary instant at the start of the Big Bang). If you think of all of the space and time in our Universe, from its beginning to its end, this is the "end-point", going backwards in time, and there is no time at all, in our Universe, prior to that.

However, as discussed at http://cseligman.com/text/prologue.htm , the nature of the Cosmic Background Radiation and theories of quantum fluctuations in empty space time both converge on a theory of our Universe's origin, from a single point of space-time in another Universe. So if you want to go backwards from our beginning, you could say that there was some unknown time prior to the start of our Universe, when our Universe did not yet exist, but the one from which our Universe was formed, did exist.

However, as noted on that page, in the instant of the fluctuation which created our Universe, a whole new spacetime was created (our Universe), which was completely separate from the old one, so that no one in the "old" Universe could detect the existence of the new one, and there is no way, in the "new" Universe (ours), that we can detect the existence of the "prior".

This theory leads to the idea that there are an infinite number of Universes, each of which is capable of creating countless other Universes, going forward in time forever (if not in one Universe, then in others originating from it), and backwards in time for an unknown but presumably very large (and possibly infinite) time. It's just that, unlike the science fiction idea of "parallel" Universes, there is no connection between any Universe and any of the others, as each has its own completely independent and separate spacetime, so for any inhabitant of one of them, there is a fixed moment in time which is the absolute "beginning", so far as that Universe is concerned.

That is what is meant by the idea that the Universe started at a particular moment in time, with no time before that. Not that there mightn't have been prior time in some prior Universe, but that there is no time in our Universe, prior to the Big Bang.

I hope that clears things up; but if you need further clarification, just let me know, and I'll do what I can to help. (And again, sorry about the delay, but as I noted earlier I was out all evening, and didn't have a chance to get to this until now.)