Re: Predeterminism and parallel universes

From: george murphy (gmurphy@raex.com)
Date: Thu Jul 03 2003 - 14:44:38 EDT

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    Richard McGough wrote:

    > Truce, George?

        Okay with me.

            Let me note a couple of non-quantum mechanical matters which raise questions about Tegmark's claim.

            First, a relatively minor technical point. A flat space (as our universe appears now to be) is
    not necessarily infinite. It could instead have the topology of, e.g., a 3-torus. This possibility is well known & a number of people have looked for observational evidence for it, but it often gets ignored in discussions. If this were the case & the periodicity interval small in comparison with the huge distance Tegmark requires to replicate our observable universe then there would be no replication.

            The second concern is more philosophical & more serious: Can our present theories really be extrapolated to the tremendous extent required by his theory - i.e., out to 2^[(10^118)/3] Hubble lengths? It's like the "prediction" that in 10^330 seconds (or something like that) all the air molecules in my study will collect on one side of the room. Is this really a scientific prediction?

            Such questions were raised long ago by Percy Bridgman in _The Nature of Physical Theory_.
    I don't share his operationalist philosophy and, as a theorist, am quite happy to do a lot of pretty speculative playing with equations. (I once calculated that it should take ~10^80 years for the earth's wave packet to spread out over its orbit - if noboby looks at it!) But I think that even theorists whose feet aren't planted too firmly on the ground should distinguish between a "prediction" like that or like Tegmark's & predictions that if you look in a certain part of the sky you'll see a new planet, or that the 2^2^P level of hydrogen is split.

            Wild speculations are sometimes interesting & may even be true. If sciam had said on its cover, "Infinite Earths in Parallel Universes May Really Exist" it would have been OK. But leaving out the "may" was irresponsible.

                                                                                                            Shalom,
                                                                                                            George

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