Re: poly: eschatology

From: Nick Bostrom <>
Date: Mon Jan 12 1998 - 03:51:10 PST

 Hal Finney <> wrote:

> Unless there are some ad hoc topology wraparounds, the zero and negative
> curvature universes are infinite in spatial extent, with an infinite
> number of stars, unlike the closed universe.

How should we intuitively picture such an open universe if we in our
imagination travels backwards in time? In the case of a closed
universe, the picture I have is that as we travel backward in time,
the universe gets smaller and smaller (in the sense that it would
take less and less time for a light beam to come back to where it
started) until it is just a point, before which was nothing. This
point would be the Big Bang.

I'm not sure how good that mental picture is. Maybe at the extreme
conditions at big bang, time and space become mingled in such a way
that that picture is misleading? I can sort of add to my picture that
time did not exist before big bang, without giving up the basic

But in the case of the open universe, if we project backward in
time in the same simple mental model, then we seem to come to a
point in time, about 15 billion years ago, where the whole infinite
space with the infinite number of stars just pops up instantaneously
all over the place so to speak. That surely can't be the right way to
think about it? But what can we say about the spatial extention of
our universe 15 billion years ago if it's open? What's the best way
of thinking about these things intuitively? (I feel a bit
embarrased to ask, for having taken courses in GTR
and cosmology, I feel that I ougth to know this. But "Just look at
the formulae!" doesn't seem to satisfy my curiosity.)

Nick Bostrom
Received on Mon Jan 12 11:51:15 1998

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