
Gravity is unlikely to be the cause of quantum collapse, experiment suggests - tdhttt
https://www.sciencemag.org/news/2020/09/one-quantum-physics-greatest-paradoxes-may-have-lost-its-leading-explanation
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akvadrako
Gravity was never a leading explanation for collapse; it was always a fringe
idea.

Gravity is local and apparent collapse is non-local; it doesn’t even pass the
smell test.

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alpineidyll3
Collapse is only mysterious to people who never learned thermofield theory, or
non-equilibrium quantum dynamics. Unfortunately this is also a sizable
fraction of all physicists. Thus we have articles like this :/

Basically all the work in getting large scale quantum computers to work lies
in these fields. They will continue to grow.

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GuB-42
I am not a physicist but isn't it an instance of "if you think you understand
quantum mechanics, you don't understand quantum mechanics"?

The measurement problem, which deals with collapse is still unsolved. It is
also the reason why there are so many weird interpretations of quantum
mechanics and that even top physicists can't agree on one. In fact the same
physicists tend to sweep the problem under the rug and instead focus on the
equations that, to be fair, did a lot more to science and technology than
trying to solve the measurement problem.

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alpineidyll3
There is no measurement problem. It so happens that most measurement apparatus
are macroscopic and at a temperature much higher than the quantum gap of the
system being probed. Measurements in qm imply a rotation between systems, and
mixture with an incoherent thermal state implies a quantum superposition will
lose coherence. Full stop. This is all understood in full, grab any text on
non equilibrium quantum dynamics. One can even simulate the collapse process
in full detail, and obtain superior agreement with experiments.

If the measurement apparatus is coherent, measurements can be performed
without collapse. This was well thought out even within wigner and einstein's
lifetimes. c.f. the vaidman bomb detector.

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Orlanthai
It depends on what one calls the measurement problem.

This solves the "consistency/small problem", i.e. treating the macroscopic
apparatus as boolean is justified.

It doesn't resolve the "outcome problem", i.e. which outcome is selected. Of
course if you accept the world is not deterministic this isn't really a
problem.

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alpineidyll3
One could argue even classical mechanics isn't deterministic as we think of it
because of chaos, which has fascinating connections with QM. W Hoover (of the
Nose-Hoover thermostat fame) did some great work with reversible thermostats
exploring the instability of Newtons equations of motion.

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Orlanthai
I think that's different. Chaos still uses classical probability and the
randomness is just ignorance of underlying initial conditions. This is very
different from QM.

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alpineidyll3
You'd be surprised. You should read about many-body localization and the
eigenstate thermalization hypothesis.

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Orlanthai
I have. They still don't make Quantum Theory and Chaos similar. Rather for
some systems QM can motivate ergodicity as well as classical chaos can.
However that doesn't mean Quantum Probability and Classical Probability are
alike simply because they give similar behaviour for certain systems for one
specific limit. Their representation theory is completely different.

Chaotic systems don't have a Kochen-Specker or PBR theorem.

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mgraczyk
What percentage of practicing physicists actually think there is something
"missing" in the quantum formalism as it relates to "wavefunction collapse"?

I'm not a physicist, but from the few years of QM I took in college my take is
that there is nothing special about "measurement", it's just a label we apply
to certain states becoming entnagled. As long as you don't believe there is
anything magical about humans or other "conscious" observers, then there
doesn't seem to be anything to figure out about collapse.

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Xcelerate
> then there doesn't seem to be anything to figure out about collapse.

Then why is quantum state evolution seemingly continuous and unitary some of
the time, and sharply discontinuous at other times?

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im3w1l
It seems continuous and unitary when the experimenter takes a lot of care to
create a simple and very isolated system. When it's brought into contact with
the mess that is the rest of the world it changes character very quickly, and
interactions with the rest of the world completely swamp the internal
dynamics.

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tdhttt
The
[paper]([https://www.nature.com/articles/s41567-020-1008-4](https://www.nature.com/articles/s41567-020-1008-4))

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Animats
Nice. It's an actual experimental result.

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wwarner
I don't understand why we would think wave-function collapse would release
radiation.

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corey_moncure
Lazy evaluation.

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brianberns
It does seem like some aspects of QM point to reality being simulation that
tries to avoid the expense of unnecessary calculations.

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AgentME
There's no work QM is saving: it doesn't delay work or get to do less until
when you physically look at something and then get to skip work for things you
don't look at. * Things that are in superposition would require more
computation for all their many alternate versions (most of which aren't
meaningfully interacted with), not less, and the extra work for managing
superpositions continues forever if MWI is right. All particles are constantly
entering new superpositions, not just individual particles in fancy lab
experiments. Only the very simplest of particle interactions (like two
individual hydrogen atoms interacting) are feasible to simulate with full
quantum mechanics on classical computers. * "Observation" happens through any
physical interaction at all, including particle collisions. Outside of some
individual particles inside carefully controlled experiments, most particles
end up transitively interacting with most other particles near them.

If the universe was at all optimized for simulation costs for human
experience, we probably wouldn't expect there to be be trillions of galaxies
with hundreds of millions of stars each, for the smallest particles to be on
the scale of billion-billionths compared to humans, or for QM to work anything
like it does.

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saalweachter
That time-steps for atomic interactions need to be picoseconds or smaller, but
interesting biological reactions take minutes+ [eg,protein folding] is also a
PITA.

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amai
Every measurement (gravitational, electronic, magnetic etc. ) causes a
collapse of the probabilities. This has nothing to do with quantum mechanics.
This is simply statistics/math and has nothing to do with physics.

A simple example: As long as one doesn't look at a coin, the probability that
it shows head or tail is 50%. After the measurement it "collapses" to 100% for
one of the options.

But the "collapse" is only a mathematical "collapse", not a physical one.

Physics only limits how precise and fast your measurement apparatus can be.

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TheRealPomax
"Now, one of the most plausible mechanisms for quantum collapse—gravity—has
suffered a setback." no it hasn't: stop trying to inject drama where there is
none.

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mrwnmonm
I read it "Gravity is unlucky"

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mrwnmonm
Why in the hell I get downvoted for this comment?

The world is full of freaks.

