On 9/27/2011 9:13 PM, Jason Resch wrote:
On Tue, Sep 27, 2011 at 10:52 PM, meekerdb <[email protected]
<mailto:[email protected]>> 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<[email protected]
<mailto:[email protected]>>
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 universes.
Or by Feynmann paths that zigzag in spacetime. Don't become to enamored of an
interpretation.
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.
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. 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.
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."
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