On Sep 28, 2011, at 1:28 AM, meekerdb <meeke...@verizon.net> wrote:

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



On Tue, Sep 27, 2011 at 11:52 PM, meekerdb <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?

Quantum computers have been built, but last I checked it was only 7 qubits. There is no known principle which would forbid quantum computers having more qubits. Even one with a few thousand could solve problems we could not otherwise.

Anyway, the answer is by the one particle cycling back thru time, so it appears to us as many particles.


If this is a possible answer you should write David deutsch, since he says he has never received an explanation in a non many worlds framework.

Then again, if every partical is going backwards in time to cover every possibility, is that really any different? Would not all possibilities be realized infinitely often?







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.


It is interesting you should say that. Before I read your response I was going to propose my take on you aphorism: the more deep or fundamental a theory is, the less specific it will be.

Jason

Brent


Jason
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