Re: ASSA and Many-Worlds

From: Brent Meeker <>
Date: Fri, 19 Jan 2007 08:44:31 -0800

William wrote:
> I have been reading up on this subject a little bit and about the
> quantum immortality, I believe it is a common misconception that this
> means you will never die; if all future branches involve your death,
> then you will die ... Quantum immortality does not imply that you can
> dodge every bullet and that the "you of today" will still live
> tomorrow, although the "you of yesterday" could still live tomorrow
> whilst the "you of today" does not.
> Also I personally do not believe ASSA favours a MWI interpretation of
> quantum mechanics over a deterministic one because a "single MWI
> universe" will be less probable than a "single deterministic universe".
> But it might favour MWI over Copenhagen interpretation.
> If the universe splits into 2 universes each second; I do not
> necissarily see an issue as explained by Stathis Papaioannou in his
> post. And it is even a fact that you are more probable to live in the
> year 2000 than in the year 1000 because the human population has grown;
> but once we go to infinities, the same approach might not work anymore
> (although I am still debating about this myself) ...
> Anyway, I do not believe that MWI favours later moments in time over
> earlier moments in time. Although the number of universes increases,
> their individual probability decreases, keeping the total probability
> equal (although relativity might complicate a more rigorous approach).
> A simple way of picturing this, would be that at the big bang; the
> universe is 1 piece of paper, and from then on, every second, the
> piece(s) of paper is cut in half; giving 1, 2, 4, 8, ... universes. The
> total area of paper remains the same and all the pieces get smaller all
> the time, this means that the chance of being in a particular universe
> as the universe splitting progresses, even decreases :).

That's a good way to look at it. Everett originally called his interpretation a 'relative state'; emphasizing that observed states were relative to the observer. 'Multiple universes' is a convenient way of talking, but the idea comes from holding onto the unitary evolution of the state vector in a Hilbert space describing states of the universe. So there is only one universe and it is the projection onto different semi-classical subspaces (the only kind we can experience) that correspond to different 'universes'. In QM you can have negative information (due to the correlations of entanglement) and so from the Hilbert space view the total information may be zero, even though the projection onto subspaces is very complex.

I also think that the modeling of the inner product in Hilbert space as real number is probably and approximation. QM and general relativity together imply that there are smallest units of time and space, the Planck units. When a quantum theory of gravity is invented I think it may imply a smallest unit of probability - so that the arbitrarily small probabilities required for Tegmark to survive his machine gun will not exist.

Brent Meeker

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Received on Fri Jan 19 2007 - 11:45:51 PST

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