
New math proves that a special kind of space-time is unstable - furcyd
https://www.quantamagazine.org/black-holes-prove-that-anti-de-sitter-space-time-is-unstable-20200511/
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pmiller2
Here is what I believe is the most relevant paper by Moschidis:
[https://arxiv.org/abs/1812.04268](https://arxiv.org/abs/1812.04268)

I find it mildly amusing that this work is being done by mathematicians rather
than theoretical physicists.

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piokoch
I don't think theoretical physicists would find these findings to be that
interesting. There are a lot of mathematical results that can be somehow
applied to physics, but very rarely something interesting comes out of it from
physicists perspective. Obviously when it happens, then it can lead to a
breakthrough as it happened when Einstein figured out how Riemmann geometry
can be applied to GR.

The author himself is kind of uncertain if there are any real consequences
comming out of his math:

>>The instability of AdS space-time has major implications for how we
understand our own universe. First, since AdS space-time is unstable, it’s
“something you will not see in nature,” Moschidis said.<<

>>But “even though AdS is not real,” he said, “it can still lead us to the
discovery and study of real phenomena.” <<

I am not sure how our understanding of time-space can be increased by a theory
that just does not describe reality.

Maybe the math is somehow useful? Maybe this might explain what happened after
Big Bang (maybe instabilities were more common then)? Maybe this is the path
to unify QM and GR (in the article it is mentioned that, but with some usual
addition of not yet observed additional dimension that can explain everything
- the feature of many "string" theories", that didn't give us much.

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abdullahkhalids
Theoretical physics has always studied theories that don't describe reality.
It deepens our understanding of the theories that do describe reality. Eg., if
you change one axiom of a reality-describing-theory and certain naturally
occurring phenomena disappears, then you can say that that axioms causes that
that phenomena to occur.

Also, this is not my field, but thousands of physics papers have been written
on the AdS geometry (particularly the AdS-CFT duality). This line of thinking
has brought a lot of clarity to string theory and to black hole physics.

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seemslegit
“If you perturb AdS space-time and wait a sufficient time,” Moschidis said,
“you’ll end up with a different geometry — one that contains black holes — and
it’s no longer AdS. That’s what we mean by unstable.”

But our universe is known to contain black holes and yet isn't it being AdS
considered an open question ? Or is it only an open question about the
universe during its infancy ?

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frisco
Our universe is definitely not described by anti-de Sitter space. It might be
de Sitter space though.

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seemslegit
Then why do we care so much about AdS/CFT correspondance ?

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pas
The bulk-boundary equivalency. It seems it's possible to describe some models'
insides just by studying its surface. (Hence the holographic principle.)

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tzs
> If the boundary is, in fact, reflective, nothing can leak out of AdS space-
> time. So any matter or energy put into the system could potentially get
> concentrated — perhaps to such an extent that a black hole would form.

So in space-time that does not have a reflective boundary, is the implication
that matter or energy _can_ leak out? Where does it go?

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frisco
If my understanding is right, de Sitter space effectively has _no_ boundary,
in the same way that a sphere has no edge.

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nwallin
> The Stanford mathematician Jonathan Luk describes Moschidis’ work as
> “amazing. … What he’s discovered is a rather general instability mechanism”
> — one that could apply to other settings, unrelated to AdS, in which matter
> or energy is cooped up within a physical system that has no escape hatches.

So the I'm not particularly interested in the specific result, but the "rather
general instability mechanism" is potentially game changing.

Does any know how general this mechanism is? Could it apply to Navier-Stokes?

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empath75
Can someone expand on what this means for AdS/CFT?

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pontifier
When they mentioned "other settings, unrelated to AdS, in which matter or
energy is cooped up within a physical system that has no escape hatches." I
thought immediately of the fusion reactor I've been working on.

In my device, an arangement of static fields creates a region in which
deuterium energised in a specific reflects back to the center forever and has
no outlet even after non-fusion collisions.

The "instability" in my system comes because the extreme stability in the
oscillation should cause even a rare event (DD fusion) to happen eventually
with 100% probability.

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candiodari
Does this mean we're now sure that spacetime has positive curvature ( >= 0 ) ?

~~~
cft
AdS has _constant_ negative curvature. I don't think he proved that any
spacetime with a negative curvature is unstable. But experimental data so far
show that the universe has zero curvature.

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shoes_for_thee
Hey, are we emulsion floating on the surface tension of a still, multi-
dimensional pond in which we all eventually sink? asking for a friend

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hpoe
So my understanding is that the Maledecena conjecture that provide a
correspondence between AntiDeSitter Space and CFT was a crucial breakthrough
for proving string theory. Does this discovery make an impact on string
theory?

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frisco
> proving string theory

Would definitely not consider string theory “proven”.

On the contrary, its odds of being correct (much less demonstrably so) seem to
be decreasing by the year.

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strbean
I was under the impression that string theory was inherently un-provable.

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xwdv
Can anyone relate this to a human scale? What would it mean to be caught in an
unstable space-time? How could it be exploited?

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ganzuul
What is special about wave 2? Wouldn't 3...n behave the same way and result in
stability?

