Re: Infinite universe

From: Perry E. Metzger (
Date: Sat Apr 26 2003 - 08:41:34 MDT writes:
> If faster than light travel is possible, then the
> paradox becomes much worse, since there are then many more civilizations
> that could have reached us. If instantaneous faster than light travel
> (with respect to the coordinates defined by cosmic expansion) is
> possible, it becomes impossible to argue "no one has visited us because
> no one is there" -- if nothing else, you would have expected a complete
> civilization to have accidentally come forth from random particle motions
> just after the Big Bang, or to have Hawking-radiated out of a black hole
> somewhere. This civilization could then get to any place in essentially
> zero time. Of course, it's not quite this simple -- for one thing, it
> takes resources. It does mean you have to throw away either an infinite
> universe, or unlimited FTL, or most attempted Fermi paradox solutions.
> (I'd easily pick unlimited FTL)

Side note: perhaps you've come up with an anthropic demonstration of
the lack of instantaneous universal travel (although I must admit that
anthropic explanations often disturb me as much as they disturb
others.) As you note, if we were in an infinite universe and it had
unlimited FTL travel we wouldn't be here.

> For worlds to influence each other across the fourth level of multiverse,
> there would have to be a causal interaction between mathematical
> structures out there in Platospace. This doesn't happen. Complex numbers
> don't suddenly leak into the integers; the same is true for structures
> complicated enough to have observers in them.

Ah, but not quite. For example, our mathematical structure supports
the simulation of other mathematical structures, and some mathematical
structures could have multiple embedded mathematical structures that
are subtly but causally related. Certainly this wouldn't happen for
"most" mathematical structures, but there is no reason to assume one
couldn't construct one.

> In conclusion, we will probably not have any interaction with the
> inhabitants of other universes. I don't think this makes the subject
> moot, though -- the questions whether they exist and what they are like
> can still affect what we should expect to find here, as well as help us
> think about various other subjects.

There is also the question of whether you could engineer a new
universe to escape to. As you note, it might be possible to
communicate in some way with basement universes, vis:

> Even though it seems impossible to travel between different thermalized
> regions, there can apparently be some one-way communication between them.
> This is one of the subjects discussed in the paper I linked in my
> previous post -- the authors claim that if an inflating false vacuum can
> be created within our thermalized region, it may be possible to send
> "messages tightly packed in durable containers" to them.

If this were possible, then one might somehow escape the heat death of
our Hubble volume.

Similarly, one might envision "engineering" mathematical structures in
the manner described in Egan's "Permutation City".

Either of these might be very potent applications of seemingly
"useless" theory.

All of this, though, is, as you note, utter speculative crud at this
point. I in particular don't feel I understand the question well
enough to make it more than cocktail conversation for now.

> Much of the above is either an informed guess or pure speculation; please
> keep taking it with an infinitely large grain of salt and an "IIUC"
> everywhere.


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