
Guide to the Many Meanings of Quantum Mechanics - dnetesn
http://nautil.us/blog/your-guide-to-the-many-meanings-of-quantum-mechanics
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adeledeweylopez
"The Many-Worlds Interpretation has it that each time we make a measurement,
reality splits into several alternative versions, identical except for the
measurement outcome."

That's not right, the Many-Worlds Interpretation is just that the wavefunction
in the Schrödinger equation (or its generalizations) is real, and it rejects
that there's a separate process that somehow collapses the wavefunction to the
single "branch" we perceive ourselves to be in. At the metaphysical level,
there's no splitting involved, and no ontological measurements either (much
less a "we" to do the measuring).

~~~
millstone
No offense intended, but the "lost contact with empirical reality" critique
really lands for the above description of MWI. A mathematical construct (the
wavefunction) is taken as more real than basic empirical experiences like
"measurements" and "we."

~~~
cjfd
From a physics point of view this is a very strange thing to say. Why are 'we'
or 'measurements' things of special status? Because we have a soul or
something? Now, that would be a theory where an abstract concept is taken to
be more real than observable things. The measurement apparatus is also a
physical thing that should be described by the physical theory in use as would
the humans be. The very painful point about the copenhagen interpretation is
this distinction between 'normal' time evolution and the special procedure
when a 'measurement' is carried out. Actually, there exist mathematical proofs
that the normal time evolution when applied in cases where information is
transferred from microscopic stats to macroscopic ones leads to something that
looks like a collapse of the wave function but is actually a split of it. This
is as a physical theory much more attractive than giving a 'measurement' a
special status. The question what this all means is a bit more mind-boggling
though including multiple worlds and that kind of stuff. Taking 'a
mathematical construct as more real than basic empirical experiences' is
basically the history of physics and it has in the past been highly
successful.

~~~
chongli
_Why are 'we' or 'measurements' things of special status?_

Because we experience the world through our senses. Everything else is one
mathematical model or another that we’ve created. And our models aren’t even
consistent!

 _very painful point about the copenhagen interpretation is this distinction
between 'normal' time evolution and the special procedure when a 'measurement'
is carried out_

This is not a special procedure. Measurement occurs whenever physical
interactions take place. To measure a particle, we bounce another particle off
of it and then try to detect the result. The measurement is the particle
collision, not the detection. It’s like playing billiards in the dark. We
don’t know where the balls are.

 _Taking 'a mathematical construct as more real than basic empirical
experiences' is basically the history of physics and it has in the past been
highly successful._

Except for all of the times when it broke down. When one model was found to
contradict our experiments and we had to replace it with another, which later
turned out to be wrong as well. Perhaps the most embarrassing example of this,
in human history, is all of our attempts to make geocentric models work [1].

The most well-known critique of science’s institutional habit of inventing new
models whenever old ones broke down is probably Kuhn’s paradigms [2]. If
you’re interested, you’re better off reading Kuhn than anything I have to
write here. I think the best evidence for Kuhn’s thesis is the abject
disappointment we witness every time particle physicists fail to overturn the
standard model. If that’s not supremacy of measurement, then I don’t what is.

[1]
[https://en.wikipedia.org/wiki/Geocentric_model](https://en.wikipedia.org/wiki/Geocentric_model)

[2]
[https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Re...](https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions)

~~~
pontus
You say "The measurement is the particle collision, not the detection.", but
this is not right.

When two particles bounce off each other, there is no collapse according to
traditional copenhagen, instead the wave function just evolves according to
the SE. Even worse, when that particle (let's say photon) then travels to the
measurement device to interact with the particles that make up that machine,
the evolution is similarly governed by the SE. Somehow though at some point,
nature decides that a measurement has taken place and collapses the wave
function. What dictates where that happens? Honestly this way of thinking
about it makes no sense to me. The MWI is, to my mind, the simplest
explanation for all of this mayhem.

------
6nf
This recent video has a very watchable overview of several interpretations
[https://www.youtube.com/watch?v=XQ25E9gu4qI](https://www.youtube.com/watch?v=XQ25E9gu4qI)

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guerby
Sabine Hossenfelder youtube channel has nice videos about Quantum Mechanics
and interpretations:

[https://www.youtube.com/channel/UC1yNl2E66ZzKApQdRuTQ4tw](https://www.youtube.com/channel/UC1yNl2E66ZzKApQdRuTQ4tw)

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

Some quantum materiel also on Science Asylum:

[https://www.youtube.com/c/Scienceasylum/videos](https://www.youtube.com/c/Scienceasylum/videos)

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Viliam1234
> I am also personally offended that Baggott gives short shrift to
> superdeterminism. In this approach, quantum mechanics is emergent from a
> deterministic hidden-variables model which acknowledges that everything in
> the universe is connected with everything else. He either mistakenly or
> accidentally leaves the reader with the impression that these have been
> ruled out for good, which is most definitely not the case. I cannot really
> blame Baggott for this, though, because this omission is widespread in the
> scientific literature.

Please correct me if I'm wrong, but I thought that hidden-variables theory was
considered in scientific literature, and was experimentally disproved.

~~~
jostylr
Hidden variables theory was not disproved. Local hidden variables theory was
disproved, but, actually, all local theories of any kind whatsoever that say
that experiments have definite results have been disproved.

EPR is the argument that showed any local theory agreeing with the results of
quantum experiments must have hidden variables. Bell showed that any hidden
variable theory must be non-local. Conclusion: theory is non-local.

Many worlds escapes this by not having definite results of experiments or
anything else. Since anything that could happen does happen, there is no need
for non-local communication to achieve the (non)results.

Bohmian mechanics is a mathematically consistent theory (uniqueness and
existence proven for a wide range of Bohmian systems) and it gives rise to an
explanation of the quantum formalism. One can choose to dismiss because of
prejudice, but there is no mathematical or physical reason to do so. Its
biggest flaw, being nonlocal and thus philosophically (not actually)
incompatible with relativity, is what Bell established as having to be the
case for any theory with results.

The story with quantum field theory is more questionable, but there is a
perfectly fine setup with creation and annihilation of particles, thereby
being compatible in spirit with much of QFT. The biggest problem is that
technically QFT has problems with having a well-defined wave function. But
there have been Bohmian inspired methods of solving that problem, basically
using boundary conditions that respect the preservation of probabilities under
annihilation and creation.

------
ivan_ah
For anyone interested in QM foundations, last year the IQOQI Vienna had a very
interesting lecture series on Scientific Realism that many living philosophers
and scientists to discuss the matter. Very interesting exposition + lots of
different ideas presented:
[https://www.youtube.com/playlist?list=PLtIs3eEC6pzL1v_haWfzn...](https://www.youtube.com/playlist?list=PLtIs3eEC6pzL1v_haWfznvgiIqEK_dUo4)

Warning: each lecture is ~2.5h long and informationally dense so can't be
played at 2x speed.

