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From: Sam Wormley on 13 Jul 2010 23:22
On 7/13/10 9:35 PM, Rock Brentwood wrote:

> Newspapers need to learn how to properly frame stories. This is not
> some "new and sensational discovery announced here today!", but just
> an extension of what's already a running thread in the literature and
> has been for nearly 20 years (and more).
>
> If I didn't see Jacobson's name in the reference list, I would have
> called it plagarism. Look up his article in the reference list. That's
> what it's all about and this paper is just a "I'm going to add my 2
> cents so I can have an excuse to publish the same damn thing from
> 'another point of view'" type thing. The literature is replete with
> these.
>

Dr. Verlinde said he had read Dr. Jacobson�s paper many times over the
years but that nobody seemed to have gotten the message. People were
still talking about gravity as a fundamental force. �Clearly we have to
take these analogies seriously, but somehow no one does,� he complained.

His paper, posted to the physics archive in January, resembles Dr.
Jacobson�s in many ways, but Dr. Verlinde bristles when people say he
has added nothing new to Dr. Jacobson�s analysis. What is new, he said,
is the idea that differences in entropy can be the driving mechanism
behind gravity, that gravity is, as he puts it an �entropic force.�
From: Jarek Duda on 14 Jul 2010 00:59
Rock, ok - phenomenological thermodynamics has similar equations to
gravity - it only says that mathematics is universal ...
Please answer to logical/philosophical(?) question from the subject.

Having some concrete situation in our spacetime, like solution from
deterministic physics, we can introduce thermodynamical picture OVER
THIS SOLUTION: in each point of spacetime we take a ball and average
over it to get local effective statistical parameter field like
entropy or temperature - it allows to focus on SIMPLIFIED picture in
which we focus on statistically typical behavior.
The 2nd law of thermodynamics says that four-dimensional gradient of
such introduced scalar field of entropy agrees with our time arrow -
there has to be entropy minimum in Big Bang, so it probably created
the gradient...
But how such effective picture over some concrete solution can be
fundamental - The Reason?

Darwin, I couldn't find this 'coherence theories of quantum
mechanics', but what you say sounds somehow similar.
We always believed that natural 'locally maximizing entropy random
walk' was the fundamental one, it leads to Brownian motion - it's good
enough approximation for diffusion in fluids, but has nothing to do
with QM.
Now we finally have the real Maximum Entropy Random Walk and it says
exactly what was needed: that on thermodynamical level (of e.g. field
theories) we should assume 'wavefunction collapse' to the local lowest
energy state precisely like in QM - so the only nonmistical: Born's
ensemble interpretation is finally enough to understand QM.
From: Darwin123 on 14 Jul 2010 12:26
On Jul 14, 12:59 am, Jarek Duda <duda...(a)gmail.com> wrote:

> Darwin, I couldn't find this 'coherence theories of quantum
> mechanics', but what you say sounds somehow similar.
I think I used the wrong buzzwords. I think the model is more
generally called "quantum decoherence." It involves the environment
which is a complex wavefunction "continuously measuring" the sample
wave function. This eventually causes the sample wave function to
collapse into a wave packet, which resembles a particle.
The topic has gained an importance because of advances in
technology. Quantum decoherence is very important for developing
quantum computers and quantum communications. Quantum communications
are starting to be used for sending encoded messages. Look up quantum
cryptology.
Reexamination of the Copenhagen interpretation has left the field
of philosophy because of these new technological applications of
quantum mechanics. The Copenhagen interpretation is no longer the
final say in quantum mechanics. Since general relativity and quantum
mechanics still have fundamental contradictions, quantum decoherence
still isn't the final say in everything.
Quantum decoherence is more fundamental than string theory, at
least to me. String theory is a model within quantum mechanics. So I
am not surprised that a theorist wants to bring together string theory
with quantum decoherence. Quantum decoherence answers the question of
whether the electron is a particle or a wave (a wave!). Still, you one
wants to know if gravitational energy is a particle or a wave. So
efforts to unify general relativity and quantum mechanics will at some
point have to collide with quantum decoherence.
I originally went through articles and books on the subject. This
was the bad old days before "google". However, I did a short google
search for you. I came up with the following set of links.
Specific overviews of quantum decoherence
http://en.wikipedia.org/wiki/Quantum_decoherence
http://arxiv.org/abs/quant-ph/0312059
General overviews of quantum mechanical interpretations, which contain
a description of quantum decoherence.
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics
http://www.bibliotecapleyades.net/archivos_pdf/quantum_mechanics_crossroads..pdf
I didn't list every hit that came up. However, I hope these
links are a good beginning. If you seriously research it yourself, I
am sure you will come up with better links. Maybe even a few good
books, like what I used to have!
From: Jarek Duda on 16 Jul 2010 02:59
Ok, quantum decoherence interpretation says that wavefunction collapse
is thermodynamical result of interactions with environment.

The essence of thermodynamics is using mathematical theorems like
maximum uncertainty principle.
Standard random walk was successfully pretending to already do it -
its continuous limit is enough to model diffusion in fluids, but from
QM or for example recent STM pictures of electron stationary
probability density on a surface of semiconductor, we clearly see that
fixed structure of defects in condensed matter makes this approximated
thermodynamical model inappropriate.
But when we do it right - use the real Maximal Entropy Random Walk and
generalized models, we get exactly what's needed - that we should get
going to the square of coordinates of the dominant eigenvector of
(discrete) Hamiltonian - that when we cannot trace unitary evolution,
we should assume 'wavefunction collapse' - explaining this decorence
interpretation.
Here is new discussion about it:
http://physicsworld.com/cws/article/news/43203
From: Rock Brentwood on 22 Jul 2010 04:31
On Jul 13, 8:22 pm, Sam Wormley <sworml...(a)gmail.com> wrote:
> His paper, posted to the physics archive in January, resembles Dr.
> Jacobson’s in many ways, but Dr. Verlinde bristles when people say he
> has added nothing new to Dr. Jacobson’s analysis. What is new, he said,
> is the idea that differences in entropy can be the driving mechanism
> behind gravity, that gravity is, as he puts it an “entropic force.”

I read it fully now. His own account of what's new is off. The only
real things he added to the thread were: (1) a somewhat better
separation of the fundamentals (much along the lines I spelled out in
my last article, in fact) and (2) the identification of *which*
surfaces to take as "cutoff" surfaces. The other stuff was pretty much
an elaboration of what I already described in the previous article,
apart from the discussion of the interpretation of the potential.

But I've been floating a better suggestion in SPR on both fronts
lately -- (1) the Cosmological Horizon already gives you a ready-made
cutoff for the state space, by its very definition. And it grows with
time so you get something like a 2nd law as emergent (in contrast,
Verlinde's analysis took at as a postulate). Plus, you already have
ready-made horizons, over and above all this, by doing the
construction for the Noether theorem the right way.

(2) the analysis is *still* not getting to fundamentals, despite the
fact that he nearly hit on the central idea. It's still "stuck in the
present" in 1990's 2000's string-speak and Holography-speak, when all
of these issues are utterly irrelevant. The REAL issue almost alluded
to in paragraphs 4 and 5 of section 1 is that there is a breakdown of
the Noether Theorem for any symmetry that involves having to move
points.

The Noether theorem only applies to compact regions only. (And, so the
construction alluded to above, is the one made necessary by this fact
-- a local foliation of a saucer-shaped compact region generated by a
vector field that drops off to 0 on a fixed 2-D surface on the rim --
the "Noether Horizon" for lack of a better name).

For local symmetries, points are fixed, so no problem. The Noether
theorem works. For classical theory, moving a region is no problem,
you account for the difference by the boundary terms. It's "no
problem" with a proviso -- the so-called "constant" conserved currents
are not constant. They're functions of the shape of the region over
which the local foliation is done. They're functions of the Noether
horizon. If the region moves, the "conserved" currents change, unless
the symmetry leaves the horizon fixed.

But in any case: for Quantum theory -- BIG problem. When you move a
region, you change its state space and even the very definition of
"quantization". The new state space is not equivalent to the old state
space.

Part of what was in the original region is outside, part of what was
outside is inside. The result is an incomplete Bologiubov transform.
The situation is entirely analogous to what underlies the Hawking-
Unruh effect. You get an introduction of a kind of "anomalous" entropy
associated with the motion of the region -- a cut-off entropy. In
turn, this produces an anomalous contribution to the Noether current
associated with the diffeomorphism symmetry. That contribution goes on
the left-hand side the equation that has the stress tensor (the
Noether current) on the right.

There is nothing here involving issue-of-the-day-speak (i.e. AdS/CFT,
Holography, or whatever other largely fad issues have been in the
journals in the past 10-20 years). It's simply a matter of properly
addressing fundamentals.

In any case, his analysis closely fits the description I already gave.
In fact, you can even line up the equations (and this is something
even he missed).

Under "0th law": (3.8), (4.17)
Under "1st law": (3.11), (4.19)
Under "2nd law": (2.3)
Under "3rd law": (3.6), (3.10), (4.18).

The only really new idea there is that geodesic motion (meaning free
fall + inertia) only requires equations that fall under laws 0+2+3,
while backreaction requires equations that fall under laws 0+1+3. The
physical interpretation of potential is also interesting.

But, it also bears pointing out that he understated the "robustness of
the derivation" point. It's not that h-bar and c are not essentially
involved, as he pointed out, but that they're completely irrelevant.
You could actually revert the whole set of equations under section 3
to 19th century form by taking 1/(mu epsilon) in place of c^2 and
root(mu/epsilon) e^2/(2 alpha) for h. Only alpha is quasi-new. Then
all the equations (and even the explanations) start to look a whole
lot like something Lorentz has already discussed in the late 1800's or
early 1900's. These fundamentals may even be present in his 1904
paper. So, the "quantum explanation" or "string explanation" can just
as easily be recast as a Lorentz-style "electromagnetic" explanation.

This shows that NEITHER issue is at the root of the matter. Instead,
it's the issue of Noether symmetry that is, and the breakdown (as
described above) for the symmetries under the diffeomorphism group.
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