
Space Emerging from Quantum Mechanics - MichaelAO
http://www.preposterousuniverse.com/blog/2016/07/18/space-emerging-from-quantum-mechanics/
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yk
For some context, there is a very intriguing formulation of General Relativity
in terms of entropy. [1] What this suggests is, that gravity emerges from a
underlying thermodynamical system. In OP the authors construct explicitly one
of these systems.

Unfortunately together with the success of perturbative quantum gravity [2],
this suggests that quantum gravity is just not experimentally accessible.
(That's a thought by Freeman Dyson originally.) The formal argument would be,
that a lot of different theories lead to the same thermodynamical limit, so
that one can not determine the true underlying theory. Or put it in more
hacker news terms, the problem is analogous to trying to learn about TCP/IP by
looking at the output of black hole simulations, there is the layer of
numerical mathematics in between, which is at least very hard to breach.

[1] Older guestpost by Grant Remmen on Carroll's blog:
[http://www.preposterousuniverse.com/blog/2016/02/08/guest-
po...](http://www.preposterousuniverse.com/blog/2016/02/08/guest-post-grant-
remmen-on-entropic-gravity/)

[2] For this discussion, it is basically cheating. You quantize gravitational
waves on a classical background geometry. The approach works very well because
gravity is weak, it also tells us nothing interesting, because one breaks the
relationship between gravity and space time (the central feature of General
Relativity) by hand.

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heimatau
Tidbits (stars for the top two ideas):

* -* "Or, more accurately but less evocatively, “find gravity inside quantum mechanics.” Rather than starting with some essentially classical view of gravity and “quantizing” it, we might imagine starting with a quantum view of reality from the start, and find the ordinary three-dimensional space in which we live somehow emerging from quantum information."

\- "If we perturb the state a little bit, how does the emergent geometry
change? (Answer: space curves in response to emergent mass/energy, in a way
reminiscent of Einstein’s equation in general relativity.)

It’s that last bit that is most exciting, but also most speculative."

\- "But the devil is in the details, and there’s a long way to go before we
can declare victory."

\- "In some sense, we’re making this proposal a bit more specific, by giving a
formula for distance as a function of entanglement. "

\- "We’re quick to admit that what we’ve done here is extremely preliminary
and conjectural. We don’t have a full theory of anything, and even what we do
have involves a great deal of speculating and not yet enough rigorous
calculating."

* -* "Perhaps the most interesting and provocative feature of what we’ve done is that we start from an assumption that the degrees of freedom corresponding to any particular region of space are described by a finite-dimensional Hilbert space."

\- "A finite-dimensional Hilbert space describes a very different world
indeed. In many ways, it’s a much simpler world — one that should be easier to
understand. We shall see"

My 1 cent:

I don't know enough about this subject but...it's this creative thinking that
is desperately needed in the sciences. I'm not trying to tear down others but
instead just say that this is what happens when education advances. When
enough (abstract) people focus on a subject, we will find a breakthrough.

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Animats
This is impressive. Not that I understand it. But it's encouraging to try to
derive space and gravity from quantum mechanics.

Quantum mechanics seems to be how the universe really works. Outrageous
predictions of quantum mechanics, from the two-slit experiment onward, have
been experimentally verified. So it's a sound base for further work. Physics
has been stuck for a century trying to reconcile relativity and quantum
mechanics. This might be a way forward.

It might even lead to something that's experimentally verifiable.

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chmike
I would suggest reading "Space time quantization" [1] published in 1999
presenting a theory based on the same idea. This theory has since being
developped and the latest results have been submitted for publication. These
results are multiple. The most important of them are the explanation of the
nature and properties of dark matter. But there is much more.

The seeding work on this theory was published as early as 1967 and 1978.

Publication into arXiv is too restricted, because of the endorser requirement,
for the article to be published there.

[1]
[http://www.meessen.net/AMeessen/STQ/STQ.pdf](http://www.meessen.net/AMeessen/STQ/STQ.pdf)

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semi-extrinsic
I'm not casting any evaluation or judgment on the work you cite at all, but
it's a lot easier to get a paper on the arXiv than into a non-trash journal.
If the subject is too controversial to appear on the arXiv, most journal
editors will bench reject it.

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jessriedel
In fairness, Foundations of Physics (where this paper by Meessen was
published) isn't a trash journal, but it is an odd duck. The editor in chief
is Nobel laureate Gerard 't Hooft, who everyone agrees is brilliant, and
generally still rigorous strictly speaking, but whose interest have become
much less mainstream. Articles published in the journal are rarely flawed in a
technical sense, but they do often explore highly speculative avenues that are
usually considered unpromising for good reason. I'd say there's a good analogy
to cold fusion, which is a field that is highly unfashionable for good
technical reasons, and which has attracted a lot of cranks, but in which there
are still formally open problems and which can't be completely dismissed.

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semi-extrinsic
Yes, 't Hooft seems to have some interesting interests these days. I believe
he's one of very few who think superdeterminism is a tenable explanation of
entanglement.

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jessriedel
Yep. Here's him talking about it at the Perimeter Institute:
[http://pirsa.org/displayFlash.php?id=15050094](http://pirsa.org/displayFlash.php?id=15050094)

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dasil003
This sounds super interesting to me as someone with a passing interest in
astrophysics but no real study. But it also seems such an obvious approach
that I'd be shocked if it hadn't been tried before. Is it really that novel?

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chmike
See my other comment about "Space time quantization".

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themgt
This has seemed to me for a while the right approach (gravity from quantum
mechanics, vs. quantized gravity). Can anyone speculate on the discovery of
"gravitational waves" \- i.e. in a quantum mechanical description, what are
gravity waves made of? A sort of quantized spread of entanglement?

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tlogan
I don't know enough about this subject so I would like to ask the following.

Does this means that gravitation "force" can be actually just a function of
entanglement (between regions of space, particles, etc.)?

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grondilu
Basically, yes. Although gravitation is not a "force" but a manifestation of
the geometry of space-time. The aim is to show that this geometry can be
derived from entanglement relations in the Hilbert space.

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grondilu
It's way above my league, but possibly related is an old article from nature
communications, "Quantum correlations with no causal order":

[http://www.nature.com/ncomms/journal/v3/n10/full/ncomms2076....](http://www.nature.com/ncomms/journal/v3/n10/full/ncomms2076.html)

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sevenless
I don't see what's testable or falsifiable in here. Okay, it's good to get rid
of epicycles, and intellectually pleasing, but it still looks like the same
objections apply as have been raised around string theory. Even if this _is_
the 'theory of everything', will we not end up with shorter equations that
describe the same observations?

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tim333
If they do find a way to predict space and gravity from quantum mechanics it
probably will have testable predictions. They don't seem to have cracked it
yet though. (Disclaimer - didn't read the paper.)

I've long thought this would be a good way to go for research. I once had a
crack at understanding Feynman's arguments that you could get general
relativity from spin-2 particle theory in the book Lectures on Gravitation
based on his 1965 lectures with the intention of writing a simplified version
for Wikipedia. I failed - too hard - maybe someone else can do a laymans
version? As far as I know there hasn't been very much progress since Feynman's
attempts which were not renormalizable.

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mattfrommars
What's unique about gravity which is different from other forces?

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Retra
It is a ficticious force:

[https://en.wikipedia.org/wiki/Fictitious_force](https://en.wikipedia.org/wiki/Fictitious_force)

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JumpCrisscross
Wait, is this suggesting gravity is really entanglement writ large?

