From: Lee Corbin (lcorbin@tsoft.com)
Date: Thu Aug 15 2002 - 20:01:03 MDT
Rafal asks
> > A question:
> >
> > If the Universe is open, how many galaxies does it contain? Is it an
> > infinite number? Is it finite in a closed Universe? How many galaxies
> > in the perfectly (large-scale) flat universe?
No one knows the topology for sure. But over time I came to
the startling revelation that no one has provided evidence
that there aren't infinitely many galaxies. I believe that
there are.
> > I don't mean galaxies seen from a given point, I mean all galaxies
> > countable
> > by a demon not constrained by the speed of light (presumably much
> > larger than Maxwell's).
Mike writes
> How much is 1 divided by 0? Presupposing faster than light demons
> creates a non-sensical question. It's like asking "If an angel were
> dancing on the head of a pin, how far away would the horizon of the
> pin-head appear to be to the angel?"
Rafal was actually asking about ontology: that is, what is the
cardinality of the set of galaxies under various theories? (He
was trying to make it an operational question, but some will
perhaps rightly find that more confusing, not less.)
If the universe is closed, then there are finitely many galaxies,
and the universe can even be said to have a radius. But if the
universe is open, then like I say, there probably exist aleph
zero (i.e. countably many) galaxies.
Lee
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