# All possible worlds in a single world cosmology?

From: Stathis Papaioannou <stathispapaioannou.domain.name.hidden>
Date: Sat, 17 Jul 2004 20:46:48 +1000

I have been wondering about the possibility that all possible worlds exist,
but sequentially rather than simultaneously, under a conservative cosmology
with assumptions as follows:

1. There exists one, and only one, real, physical universe;

2. While it is possible to simulate any subset of this universe, including
conscious beings, with a computer program, this program must be implemented
on a physical computer, or on a virtual machine (or series of such) which is
itself implemented on a physical computer;

3. The universe has a finite age and is comprised of a finite amount of
matter/space/energy, but it is expanding and cooling and will continue to do
so forever;

4. Some single world interpretation of quantum mechanics is correct.

My understanding is that the above assumptions, which I have deliberately
chosen as being contrary to many of the ideas discussed on the Everything
List, still allow for the possibility of fantastically unlikely events, such
as the spontaneous formation of an exact and stable copy of our solar system
from the random motion of particles in interstellar space, or from vacuum
fluctuations posited by the Uncertainty Principle.

Let p(t) = probability that an event P will occur somewhere in the universe
during the next year, t years from the present. The probability that P will
NOT occur at some time between the present (t=0) and (t=a+1) is then given
by the product:

[1-p(0)]*[1-p(1)]*[1-p(2)]...*[1-p(a)]

As a-> infinity this becomes an infinite product, representing the
probability that P will NEVER occur. It is easy to see that this infinite
product diverges to zero in the special case where p(t) is constant for all
t; in other words, that P, however unlikely, will definitely occur at some
point in the future if the probability that it occurs during a unit time
period remains constant over time. The same conclusion applies if p(t)
increases with increasing t: the infinite product diverges to zero, more
quickly than in the case of constant p(t).

Things get more difficult, however, if p(t) decreases over time. A Google
search for "infinite product" brought up some very complicated expressions
for even rather simple p(t), and it is by no means obvious (to me, anyway)
whether the product will converge or diverge.

Now, my question is, what happens to p(t) over time? I would have guessed
that as the universe expands, chemical and nuclear reactions are less likely
to occur, in the same way as chemical reaction rates are proportional to the
concentration the reagents. On the other hand, it is not clear to me how
more exotic processes such as spontaneous appearance of particles out of the
vacuum are affected by the expansion, which after all results in "more
vacuum" - doesn't it?

I'm sure the above is a gross oversimplification - I'm not a physicist - but
I would welcome people's thoughts on it.

Stathis Papaioannou

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