
Quantum magic: A skeptical perspective (2011) - lainon
https://arxiv.org/abs/1107.3800
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Strilanc
> _We argue that many popular "quantum paradoxes" stem from a confusion
> between mathematical formalism and physics [...] most "conceptual puzzles"
> of QM are not much different from the well-known paradoxes from probability
> theory_

This is really really true. Particularly for any experiment with "delayed
choice" in the name, where pop-science explanations follow correlations
backwards instead of forwards then confuse correlation for causation and start
talking about time travel ( _sigh_ ).

~~~
mlevental
i would love to see a translation of quantum paradoxes to probability
paradoxes - e.g. quantum tunneling is the same as basically measure 0 events.

~~~
k__
Or what about wave particle dualities?

How can one particle interfere with itself?

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tbabb
Personally I think the concept of "particle" needs to go away completely.

I think really what "particle" means is that "all measurements are quantized".
But the probabilities of any given measurement happening flows around as a
wave.

For example, "there is a quantity of energy `e` at location `x`" is an
observation you could make. The answer to that question has a discrete yes/no
answer. The probability of the answer being "yes" flows around like a wave
between all the different possible `x` as time progresses.

~~~
hyperpallium
IIRD doesn't the double-slit experiment show it goes through one or the other?

~~~
tbabb
No. It goes through both. That's the weird thing that double-slit tells us,
especially because it remains true even for "one photon" (i.e. one quantized
energy packet arriving somewhere on the detector screen).

~~~
k__
Wasn't it that particles went through both if you measure at the screen that
shows the patterns and they went through one if you measure at the screen with
the two slits?

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pjs_
The paper is _way_ more nuanced than the abstract suggests. There are huge
numbers of papers on the arXiv which try to say, "quantum mechanics is normal
and boring, these fools are trying to dress it up as something special because
they don't understand probabilities". This paper is more interesting. Here's a
quote:

> _In fact, QM is so weird and surprising that even the very esoteric
> interpretations, such as the many universes one, can not capture the
> subtlety normally associated with quantum paradoxes. For example, theorems
> such as the Kochen-Specter theorem [23] (essentially, a generalization of
> EPR with three particles) imply that during its quantum evolution no
> ”classical” variables can fully describe the probabilities of a quantum
> system._

~~~
dbranes
The following of course is a comment on the quote not on your comment, but no
Kochen Specker is not a generalization of EPR to 3 particles. It's easy to
come up with a generalization of EPR in 3 particles - just exhibit a 3-party
entangled state! (e.g GHZ state). K-S theorem exhibits something a lot more
subtle than entanglement known as contextuality. There are examples of systems
which have the K-S property but doesn't have any entanglement.

------
tbabb
A few thoughts:

The Monty Hall comparison is about shifting human knowledge about an
underlying system with a definite state. What, then, is the source of the
uncertainty in QM in this author's view? It is not our _knowledge_ about the
"true state" of things, because of course there _is_ no single true state.

The same could be said about any appeal to "perturbations" from the
measurements we make-- in order for a "push" from our measurement instruments
be the source of uncertainty, we must explain it in terms of an unknown
disturbance making a precise value imprecise (otherwise, the use of "our
instruments" as an explanation for "uncertainty" can't be the final tortoise
upon which the world stands). Because of the impossibility of a "precise
physical value" this explanation doesn't seem satisfactory to me.

It seems the article (like many interpretations) does no better than to say
"don't ask" about what lies underneath those probabilities. At best it says
"our knowledge is uncertain" but then stops before it says precisely what we
are uncertain about.

His points about analogues with classical probability are well taken, but I
don't think they suffice to explain or dismiss quantum "weirdness", though
it's quite possible I missed the point he was trying to make.

In particular, the article sweeps many-worlds away too quickly, IMO. Many
worlds is what we get if we assume that observers are ensembles of particles
which can exist in a state of superposition, just like any other ensemble of
particles in the universe. "Wavefunction collapse" is what such an observer
would expect to see upon becoming entangled with another system, without any
additional a priori assumptions. Fundamentally it means that, after
measurement, we cannot treat the system and the environment (and the observer
therein) as separate-- another way of stating the phenomenon of decoherence.

In other words, I think it is not unparsimonious to assume that "multiple
universes" exist, because we already know that ensembles of particles exist in
a multitude of states. We simply note that the universe, too, is an ensemble
of particles and draw a straightforward conclusion from well-established
facts. To me, it seems almost more ontologically bold to _reject_ this.

It is _also_ not unparsimonious to assume that "multiple universes" exist,
even after measurement, because delayed-choice eraser demonstrates that
wavefunctions can be "un-collapsed"; that is to say re-combined with the other
superpositions that Copenhagen supposes "disappear" after measurement. It fact
it seems to me a fairly clear refutation of (common presentations of)
Copenhagen-- But perhaps the author is on my side about that one.

Either way, this article seems to be a quite thoughtful overview, and I quite
agree there's a lot of confusion and woo both within and outside the field.

~~~
naasking
> It is not our knowledge about the "true state" of things, because of course
> there is no single true state

That's a biased statement. There is more than one interpretation of QM in
which your statement is completely incorrect. The math isn't telling you there
is no state, that's a property you've assigned to the math given an
interpretation. The paper's analogy to the Monty Hall problem would make
perfect sense given another interpretation.

