On Tue, Sep 27, 2011 at 10:52 PM, meekerdb <meeke...@verizon.net> wrote:

> On 9/27/2011 8:07 PM, nihil0 wrote:
>> On 9/27/2011 4:18 PM, nihil0 wrote:
>>  1) There is an infinite number of Hubble
>>>> volumes in our universe, which are all casually disconnected (as the
>>>> theory of inflation implies). 2) There is a limit on how much matter
>>>> and energy can exist within a region of space of a given size, such as
>>>> a Hubble volume. 3) There is only a finite number of possible
>>>> configurations of matter, due to the Uncertainty Principle.
>>>> I can explain any of these ingredients in more depth if you'd like me
>>>> to, but I hope you see that they lead to the conclusion that all
>>>> quantum-physical possibilities in our universe are realized infinitely
>>>> many times.
>>> On Sep 27, 7:47 pm, meekerdb<meeke...@verizon.net>  wrote:
>>  No they don't.   There's an implicit assumption that what happens in
>>> these other universes
>>> has the same or similar probability distribution as we observe in ours.
>>>  A reasonable
>>> assumption, but not a logically necessary one.  I think it's what Bruno
>>> means by
>>> "homogeneous".  It's logically possible that all but a finite number of
>>> these universes
>>> are just exact copies of the same completely empty universe, for example.
>>> Brent
>> You imply that it's logically possible that there is only a finite
>> number of universes that are filled with matter, and you seem to think
>> few will resemble ours.
> 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

>  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.

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. 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
>> 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. A crude estimate suggests
>> that the closest identical copy
>> of you is about ∼ 10^(10^29)m away. . ." (The Multiverse Hierarchy,
>> section 1B, http://arxiv.org/abs/0905.1283**)

Thanks for posting this.  I had mentioned it recently, but not without all
the references.


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