Re: Why our universe is open.

From: Fred Chen <>
Date: Mon, 21 Aug 2000 20:40:50 -0700

Saibal Mitra wrote:

>An interesting question can now be asked: Does the prisoner only exist
when the computer is simulating his universe, or does his universe
>exist independently of our universe and simulating his universe simply
means that we can take look at his universe and even interact with him?
>If the latter is true then clearly all possible universes exist
independently of each other. We can then ask why we find ourselves in
this0 >universe instead of the rather boring universe of the prisoner. I
think that this must follow from probabilistic arguments. It may be that
all >universes are, in some sense, equally likely a priory. The
probability that we find ourselves in a particular universe would then
be given by an >appropriate conditional probability. When we refer to
our universe we actually refer to a large class of universes, because we
don't have >complete knowledge of our universe (we can only store a
finite amount of information in our brains). So, given the knowledge we
do have, we >live in a large number of universes ``simultaneously´´, and
the number of ``equivalent´´ universes increases with its size. We
should thus ask >for the probability that we live in any of the
equivalent universes. It is thus clear that ``our´´ universe is
infinitely more likely than the >prisoner`s universe.

As Russell has posted, the prisoner's universe is "over-specified" and
so is actually more complex than our universe. However, if it is true
that a Turing machine such as the Game of Life can realize a
self-conscious being, then one wonders whether such a simply constructed
universe would have less information and be more probable.

>Interestingly this fits in well with observational evidence that our
universe is flat. From the arguments I gave above, you would expect that
the >universe is spatially open, because such an universe has an
infinite volume. This infinite volume also cause me to exist in an
infinite number of >places simultaneously in a single universe, because
the probability that somewhere an intelligent being emerges that has
stored in his brain the >same information as in my brain is extremely
small but strictly larger than zero due to the finiteness of the amount
of information that can be >stored in the brain. It would, of course,
necessarily be the case that this intelligent being is very, very
similar to me and that he lives on a planet >which is very similar to
the earth. Now it would be reasonable to expect that an universe where
the density of ``copies´´ of me is larger is more >probable. By
increasing the matter density of the universe I can increase the number
of copies of myself, but if the matter density becomes too >large then
the universe would be spatially closed. Therefore it is reasonable to
expect that we live in a flat universe.

A flat universe (omega=1) is most consistent with cosmic inflation,
which is the simplest theory that would explain large-scale homogeneity
in the universe. Other theories allow open inflation, but are more
complicated in certain ways. Simpler theories go hand-in-hand with
greater measure. It is often tempting to appeal to anthropic reasoning
to justify the matter density we observe, but we have to beware of a
theory of everything may come along which will make all the numbers
which allow us to exist obvious.
Received on Mon Aug 21 2000 - 20:43:19 PDT

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