poly: Opne and baby universes

Forwarded from Mitch (isn't he on this list? If not, then I think we
should invite him).

From: Mitchell Porter <mitch@thehub.com.au>
Subject: baby universes and open universe
To: asa@nada.kth.se
Date: Sat, 17 Jan 1998 15:45:56 +1000 (EST)

I wonder if the concept of baby universes is cast into doubt by
evidence for a spatially infinite universe?

It's hard to see how a spatially infinite universe can be
produced by the straightforward version of "baby universe"
reproduction - i.e. a collapsing finite region pinches off and
becomes an expanding finite hypersphere - since a spatially
infinite universe has to start infinite in extent.

In a "minisuperspace" quantum cosmology model you could
probably describe tunneling from a closed finite space
to an infinite open one, but only by adopting a finite-dimensional
simplification. In practice, an infinite space has infinitely
many degrees of freedom, unlike a compact space (assuming
something like the Bekenstein bound). I can't think of a
physical way to model a transition from finite to infinite
complexity.

On the other hand, perhaps the universe is only "locally"
(on a scale of >10 billion light-years) hyperbolic. Think
of a saddle-point on a mountain range, which is a region
on the (finite) surface of the Earth which is locally
hyperbolic.

Incidentally, if space really were Euclidean-in-the-large, it
could still be finite, by having a torus (T^3) topology.

I'd be interested to hear polymath's thoughts on all this;
feel free to forward this message there.

-mitch
http://www.thehub.com.au/~mitch

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Anders Sandberg                                      Towards Ascension!
asa@nada.kth.se                            http://www.nada.kth.se/~asa/
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