On 9/27/2011 10:40 PM, Jason Resch wrote:


On Tue, Sep 27, 2011 at 11:52 PM, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 9/27/2011 9:13 PM, Jason Resch wrote:


        I don't think that.  I just noted it's logically possible, contrary to
        assertions that our universe must be duplicated infinitely many times.


    If our universe is not duplicated a huge number of times, then quantum 
computers
    would not work.  They rely on huge numbers of universes different from ours 
aside
    from a few entangled particles.  Even normal interference patterns are 
explained by
    there existing a huge number of very similar universes.

    Or by Feynmann paths that zigzag in spacetime.  Don't become to enamored of 
an
    interpretation.


If you assume there is a single photon interfering with itself, how is it that this one particle can evaluate a problem whose computational complexity would exceed that of any conventional computer using all the matter in the universe?

Has such a problem been solved? Anyway, the answer is by the one particle cycling back thru time, so it appears to us as many particles.




            However, according to Vilenkin, Greene, and
            Tegmark, a generic prediction of the theory of inflation is that 
there
            is an *infinite* number of Hubble volumes (what you are calling
            universes).  Let's call the hypothesis that all quantum-physical
            possibilities are realized infinitely many times "the hypothesis of
            Cosmic Repetition". Brian Greene argues for this hypothesis quite
            persuasively. He says, "In an infinitely big universe, there are
            infinitely many patches [i.e., Hubble volumes]; so, with only 
finitely
            many different particles arrangements, the arrangements of particles
            within patches must be duplicated an infinite number of times." (The
            Hidden Reality, pg. 33)

        It's plausible - but not logically required.  Suppose all the infinite
        universes are number 1, 2, ...  Number 1 is ours.  Number 2 something
        different.  Numbers  3,4, ...inf are exact copies of number 2.  So 
there are
        only two arrangements of particles; in spite of there being infinitely 
many
        universes.


    Not logically required, but I would say it is not consistent with our 
current
    theories and observations.




            As for the probability distribution of matter and/or outcomes, I'll
            let Tegmark do the explaining:

            "Observers living in parallel universes at Level I observe the exact
            same laws of physics as we do, but with different initial conditions
            than those in our Hubble volume.


        This is questionable.  Most theories of the universe starting from a 
quantum
        fluctuation or tunneling from a prior universe assume that the universe 
must
        start very small - no more than a few Planck volumes.


    The generalized theory of inflation is eternal inflation.  It leads to an
    exponentially growing volume which expands forever.

         This limits the amount of information that can possibly be provided as 
initial
        conditions.  So where does all the information come from?


    I haven't heard the theory that there is an upper bound on the information 
content
    for this universe set by the big bang.

    In one Planck volume there is only room for one bit.  That's the 
holographic principle.


Yet our universe appears to take more than 1 bit to describe, and it seems to have a possibly infinite volume.


That's why I provided the (possible) explanation below.



    As to where information comes from, if all possibilities exist, the total
    information content may be zero, and the appearance of a large amount of
    information is a local illusion.

         QM allows negative information (hidden correlations) so that one 
possibility
        is that the net information is zero or very small and the apparent 
information
        is created by the existence of the hubble horizon.


            The currently favored theory is that
            the initial conditions (the densities and motions of different types
            of matter early on) were created by quantum fluctuations during the
            inflation
            epoch (see section 3). This quantum mechanism generates initial
            conditions that are for all practical purposes random, producing
            density fluctuations described by what mathematicians call an 
ergodic
            random field. Ergodic means that if you imagine generating an 
ensemble
            of universes, each with its own random initial conditions, then the
            probability distribution of outcomes in a given volume is identical 
to
            the distribution that you get by sampling different volumes in a
single universe.

    That's not what ergodic means.  In the theory of stochastic processes it 
means that
    ensemble statistics are the same as temporal statistics.  In the eternal 
expansion
    theory it is not assumed that the physics is the same in each bubble 
universe.


This one "bubble" is infinitely big according to eternal inflation.

I don't think it is necessarily spacially infinite. But in anycase the the theory of eternal inflations is that new bubble universes are eternally created. Some are finite and collapse in a big crunch. Others, like ours, expand indefinitely.

      It is hypothesized that the spontaneous symmetry breaking that results in
    different coupling constants for the weak, strong, EM, and gravity forces is
    random.  That's how it provides and anthropic explanation for "fine-tuning" 
- we're
    in the one where the random symmetry breaking was favorable to life.


This is one hypothesis to explain fine tuning, I am not sure how well it is 
supported.



            In other words, it means that everything that could
            in principle have happened here did in fact happen somewhere else.
            Inflation in fact generates all possible initial conditions


    But it's not initial conditions.  It's random symmetry breaking.


            with non-zero probability, the most likely ones being almost uniform
            with fluctuations at the 10^5 level that are amplified by
            gravitational clustering to form galaxies,
            stars, planets and other structures. This means both that pretty 
much
            all imaginable matter configurations occur in some Hubble volume far
            away, and also that we should
            expect our own Hubble volume to be a fairly typical one — at least
typical among those that contain observers.

    But this sort of undercuts the need for the anthropic explanation.  If our 
universe
    is "typical" (i.e. probable) then there's no need to invoke infinitely many 
others
    to avoid the "fine-tuning" problem.  You could just say it's the more 
probable one
    and so it's the one that happened.

    Brent
    "If an explanation could easily explain anything in the given field, then it
    actually explains nothing."

Which explanation is this referring to?

Scientific explanations in general. The first chapter, "The Reach of Explanations" is about the difference between good explanations and bad explanations. He argues that it is not a question of testability, as sometimes claimed, but of scope and specificity.

Brent


Jason
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