Re: "instant" of the Big-Bang


"Bill Hobba" <rubbish@xxxxxxxx> wrote in message
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"Pmb" <peter102560_nospam@xxxxxxxxxxx> wrote in message
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I'm reading the text "Principles of Physical Cosmology," Peebles,
Princeton University Press (1993). On page 6 Peebles writes

---------------------------------------------------------
If there is an instant, at a "big bang," when our universe started
expanding, it is not in the cosmology as now accepted, because no one has
thought of a way to adduce objective physical evidence that such an event
really happened.
---------------------------------------------------------

Does anyone agree with this either in part or in whole?

Well, since it is the birth of space-time, speaking of an instant when it
happened seems a bit meaningless.

Since we don't know what happends before a short time before the big bang
then we have no basis for saying that it was the birth of spacetime. In
fact, as I recall, the Pre-Big Bang theory holds that spacetime always
existed. But I'm rusty on that theory so it'd be wise to double check this.

However, according to inflation, it started out as a quantum field (the
false vacuum) that experienced a fluctuation that became the big bang.
But using adjectives like 'became' etc would seem fraught with danger,
since they imply time, which this was the birth of. IMHO, one can only
describe such things mathematically.

In flation does not bring us back to t = 0

I remember John Baez once posting some stuff about theories where it
started out as one dimension that gradually developed into 4 (or perhaps
more - with some being compactified) - so even speaking of an instant when
time began may be false. I suppose the development would be described by
some parameter that when it reaches some value corresponds to time but
until that value we can't speak of time even existing - notice the use of
when - see what I mean by you really need mathematics?

Best regards

Pete


.

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