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Magical Universes

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  • Alan Forrester
    Once in a while the subject of Harry Potter universes in which the laws of physics don;t seem to work and magic happens crops up. There is something we
    Message 1 of 41 , Jun 8, 2004
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      Once in a while the subject of Harry Potter universes in which the laws of physics don;t seem to work and 'magic' happens crops up.

      There is something we should note about them, which can be seen by looking
      a quantum computer running some quantum algorithm, say Shor's algorithm for
      factoring products of large primes. Every time you run this algorithm there
      is a certain probability p < 1 that it will fail. After n runs the
      probability that it will fail all n times is p^n, which very rapidly gets
      very small.

      So the parts of the multiverse where it always fails have very low
      probability compared to other parts of the multiverse.

      Also, since the algorithm always fails in these regions, the output doesn't
      depend on the input and so information can't really be said to flow in
      these regions so they don't consitute universes.

      Similarly, we can look at the Harry Potter universes as regions of the
      multiverse where the 'compute a universe' computation fails and not as
      universes in their own right.

      Alan
    • Bruno Marchal
      ... OK. I think we agree completely. I guess you agree that, once we accept physics is emergent, we need to have some theory about what can be everyday
      Message 41 of 41 , Jun 16, 2004
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        At 14:09 15/06/04 +1200, Brian Scurfield wrote:

        > > -----Original Message-----
        > > From: Bruno Marchal [mailto:marchal@...]
        > > Sent: Tuesday, 15 June 2004 02:15
        >
        > > >Obviously technical information is
        > > >physical, but it is not at all clear to me (and others) that everyday
        > > >information can be given a purely physical characterization.
        > >
        > > I understand and agree that it is not obvious that everyday
        > > information (in your sense) is physical.
        > > Now, I disagree that it is *obvious* that technical information
        > > is physical.
        > > I doubt there is anything primary "physical".
        >
        >I do agree that the ultimate explanation of everything is probably not a
        >physical explanation. That is, [take note Alan :)] physics is emergent.
        >But I was trying to point out that technical and everyday information are
        >different kinds of beast and that they live in different realms. You are
        >saying that ultimately, going back through the layers of emergence,
        >everything belongs to one realm: the epistemological (with lashing of the
        >arithmetical). Given that the physical world is real - though emergent -
        >it is valid to say that technical information is physical. We can measure
        >technical information in a precise way in the physical world, something we
        >cannot do with everyday information.

        OK. I think we agree completely. I guess you agree that, once we accept
        physics is emergent, we need to have some theory about what can be
        "everyday information" ,and then we need to explain, starting from such a
        theory (or a from some weaker theory), how the notion of technical
        information can arise.

        Bruno

        http://iridia.ulb.ac.be/~marchal/
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