
A Physicist Trying to Fix Quantum Mechanics - wallflower
https://www.nytimes.com/2020/06/25/magazine/angelo-bassi-quantum-mechanic.html
======
lisper
TL;DR: Physicist Angelo Bassi is trying to experimentally test the GRW
collapse model [1], which is in fact experimentally testable. Personally, my
money is firmly on the side of these experiments failing, but I would not bet
my entire life savings on it. These experiments may well succeed, and if they
do, that will be the biggest breakthrough in physics in 100 years. It's great
that someone is actually testing this.

[1][https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...](https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory)

~~~
hatmatrix
Interesting that such a potentially grand idea is published unceremoniously in
a specialized journal (Physical Review D).

~~~
leephillips
Physicists generally publish their physics in physics journals. There is
usually no public ceremony involved.

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Mugwort
I disagree that quantum mechanics needs fixing. What it requires is
understanding. Many people even ones with PhDs don't really have a deep
understanding of QM.

Ask a grad student or even a professor of physics what is essentially
different about QM verses classical mechanics.

I almost always get one of two answers.

QM has operators acting on a Hilbert space (rigged HS). It's so mysterious
because we have to replace everything with operators. well...

Have they heard of the Koopman–von Neumann formulations of classical
mechanics? It's CM formulated using HS and ops.

[https://en.wikipedia.org/wiki/Koopman%E2%80%93von_Neumann_cl...](https://en.wikipedia.org/wiki/Koopman%E2%80%93von_Neumann_classical_mechanics)

Another answer is uncertainty. QM has uncertainty. Well... so does classical
mechanics!

So what is different? That's a very long answer but one thing is the Exclusion
principle.

Besides the KvN formulation is it possible to do QM using the equations of CM
in the same form?

yes, it is. The Wigner Moyal Weyl formulations of QM. Look it up or Moyal star
products.

Lastly, the collapse of the wave function.

Already done long, long ago by John von Neumann in his book on Quantum
Mechanics. The correct formulation involves the subtle concept of decoherence.
Von Neumann's trace operators are used in extreme cases where standard
calculations (which involve a tiny bit of cheating) won't work, e.g. black
hole entropy.

What's wrong with QM? So far nothing! It's possible someone might find a flaw
but it hasn't happened.

The problem is mostly US. We don't understand all the implications of what we
already possess. The enormous amount of myth making and lack of understanding
surrounding QM obfuscates what the true problems are which in 99% of cases is
the most physicists simply haven't studied von Neumann carefully enough.

~~~
Strilanc
In Scott Aaronson's paraphrased words...

Quantum mechanics is just statistics, but operations preserve the 2-norm
instead of the 1-norm. Instead of case weights (probabilities) adding up to 1,
the squares of case weights (amplitudes) add up to 1. Everything else (the
uncertainty principle, measurement mattering, no cloning, Bell inequalities,
etc, etc, etc) follows.

~~~
codethief
> Everything else (the uncertainty principle, measurement mattering, no
> cloning, Bell inequalities, etc, etc, etc) follows.

Did Aaronson provide a source for that?

~~~
Strilanc
He usually explains the details right after stating it. For example, you can
follow along in his lecture notes:
[https://www.scottaaronson.com/democritus/lec9.html](https://www.scottaaronson.com/democritus/lec9.html)
.

"Statistics but with the 2 norm" is really just a succinct way of stating the
postulates of quantum mechanics, and obviously all effects of quantum
mechanics are determined by the postulates. So you shouldn't really see this
as a statement that's controversial at all.

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stared
> the wave function’s numbers have no obvious meaning

A lot of things in physics (or in other model in science, for that matter)
have cannot be measured directly. (I think "has no meaning" is a stretch
here.)

I can go for ages talking about things in physics that are less intuitive than
simple, non-relativistic, quantum mechanics (Poynting vector, anyone?)

But think about something simple and concrete: electric potential. You cannot
measure it. But you can measure its difference.

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mcnamaratw
I am not disagreeing with your overall point, but they sell meters that
measure electric potential. We measure it all the time.

~~~
AnimalMuppet
No, they measure the electric potential _difference_ between two points. This
is why, for example, you ground your scope probes.

~~~
mcnamaratw
Only the potential difference is physically meaningful. The absolute potential
has no effect on anything. You can add 1000 V or 10^6 V to everything and you
get exactly the same physics.

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whatshisface
The idea that quantum mechanics stops working at macroscopic scales is totally
unnecessary, as the fact that this _appears_ to happen has already been
explained with decoherence, which emerges naturally from the fundamental laws.
However, I guess there's something to be said for checking every imaginable
possible modification of present theories. As far as I know the only
modification that's _truly_ motivated is adding gravity to the standard model,
which nobody knows how to do, so the next best thing is to imagine extra terms
and then try to swat them out with experiments.

~~~
lisper
> The idea that quantum mechanics stops working at macroscopic scales is
> totally unnecessary

Except to explain our everyday experience of a single classical world. Then
something in QM has to give.

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archgoon
>Except to explain our everyday experience of a single classical world.

Which the parent says is explained via decoherence. Why do you feel that
decoherence does not account for the observed phenomenon?

~~~
lisper
> Which the parent says is explained via decoherence

No, that's not what the parent says. The parent says:

"The idea that quantum mechanics stops working at macroscopic scales is
totally unnecessary..."

which is true, with the one exception that I noted:

> Except to explain our everyday experience of a SINGLE classical world
> [emphasis added]

You can get from QM to multiple worlds without any ad hoc assumptions, but you
cannot get to a SINGLE classical world that way. You have to give up either
linearity or superposition.

~~~
sideshowb
The necessary emphasis in the above sentence is OUR EXPERIENCE. If you can
accept multiple worlds then you can accept the other ones are populated by
different yous each of whom experiences a single world, namely the one they
are in

~~~
lisper
It is actually much more complicated than that.

[http://blog.rongarret.info/2019/07/the-trouble-with-many-
wor...](http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html)

------
pdonis
Angelo Bassi has a number of papers on arxiv.org:

[https://www.google.com/search?q=angelo+bassi+site%3Aarxiv.or...](https://www.google.com/search?q=angelo+bassi+site%3Aarxiv.org)

This one seems relevant to the topic of the NY Times article:

[https://arxiv.org/abs/1310.8600](https://arxiv.org/abs/1310.8600)

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throwaway_jobs
This reminds me of Carl Sagan, who basically said while people believe the
beautiful math and wave functions are the fundamental reality and a universal
language, he didn’t actually believe this and thought there was something more
and very simple behind the math we use to understand/explain our observations
and make predictions.

~~~
Koshkin
Problem is, math is the only “microscope” we have a hope to peer with into the
fundamental reality. On the other hand, the wave function is just as real as,
say, the number “3” is.

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wavegeek
Given the (according to me) fact that many worlds (more aptly named the
Relative State Interpretation) is true and correct, one can confidently
predict that no "collapse" will be found. That, and the fact that people have
been looking for actual collapse of the wave function for many decades.

~~~
lambdatronics
The MWI is a cop-out. The problem of nonlocality just gets handed off to
whatever process forks the parallel universes - it has to ensure that every
universe has consistent outcomes for both halves of a Bell experiment, for
instance.

The probabilities in QM should be viewed as subjective, but physicists hate
subjectivity, so they talk about hypothetical ensembles. It baffles me that
Everett took those ensembles and decided they were real universes.

~~~
akvadrako
The MWI van violate Bell inequalities locally by using post-selection; that’s
trivial to show.

When the universe splits at two distant measurements it isn’t until those
outcomes are brought into contact that the matching of worlds needs to happen.

~~~
engineeringwoke
I know there's math that makes this seem real, but logical arguments make it
sound silly.

Does the universe split every time the wave function collapses in any form,
for all measurements of all atoms in the universe? Isn't that essentially
infinite? And how would you prove it if any of this was real?

