
Ghosts in the atom: The wave in QM may be real after all. - ColinWright
http://stirling-westrup-tt.blogspot.co.uk/2012/08/tt-ns-2875-ghosts-in-atom-unmasking.html
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madhadron
The blog article bears no resemblance to the actual math, but the issue is the
same as always: if you assume locality, you can have hidden variables. Pusey
et al assume separability (i.e., no entanglement). Hardy does so as well. It's
put in weakly and carefully, but it's still assuming locality and showing that
you can have hidden variables.

Everyone gets so stuck on the wave function. Look, if you assume that your
physical system's state is described by a vector in a linear space, that you
can project onto subspaces to describe subsets of the state, and that the
space has a metric and is complete (all sequences in the space converge to
something in the space) then if you impose a smooth dynamics on the space,
then there will be an equivalent differential equation, because there's only
one infinite dimensional Hilbert space up to isomorphism, and L2, the space of
square integrable functions, happens to be one of its faces.

The real questions is why the theory is formulated in a linear, complete
metric space. Someone posted a lecture by Scott Aaronson a few days back that
had some interesting pointers on that.

Seriously, if the wave function bothers you, just don't use it.

~~~
Dn_Ab
>if you assume locality, you can have hidden variables.

Are you sure you don't mean if you assume non locality? PBR tightens things up
beyond Bell a bit with a requirement of wave function being real itself.

Also correct me if i'm wrong but I believe the assumption is not against
entangled states but instead against entangled states via independent
preparation.

~~~
madhadron
No, I meant locality. I was more thinking the Hardy article.

~~~
Dn_Ab
Bell's theorem states no local hidden theory can be consistent with quantum
mechanics. Only non local ones are allowed.

PBR says not only are local hidden theories banned, the wave function must be
real. Unless you abandon realism of quantum states of course.

I'm not sure I understand what you are trying to say.

------
Dn_Ab
This is a very unimpressive article. I am surprised to see Colin link to it.

In particular, while the paper the article references in a short part between
the history lesson is important, it does not actually change things much.

It rules out those who think that the wave function is a distribution over an
underlying reality but it does not affect those who believe that there is no
hidden reality. So called Quantum Bayesians (imo the clearest not necessarily
best framework). Nor does it affect the Many Worlders who think the wave
function is real, and no hidden variables. Non Local Hidden Variable Theories
with real wave functions are still acceptable. So things are no where near as
clear cut settled as the article would have you think.

And even for those who believe the wave function is an epistemic tool for an
underlying reality, they can still abandon Bell's framework using exotic
escape routes like "retro causality". See Matt Leifler's blog for more on
that: [http://mattleifer.info/2011/11/20/can-the-quantum-state-
be-i...](http://mattleifer.info/2011/11/20/can-the-quantum-state-be-
interpreted-statistically/)

For a better explanation of the paper see:

[http://mattleifer.info/2012/02/26/quantum-times-article-
on-t...](http://mattleifer.info/2012/02/26/quantum-times-article-on-the-pbr-
theorem/)

<http://www.scottaaronson.com/blog/?p=822>

------
colanderman
I don't get it. Either quantum waves correctly describe particle physics, or
they don't. If the waves behave correctly in all observable ways, how can we
judge whether they are "actually" what's going on, rather than some
mathematically different – but observably identical – process?

Is it that quantum waves were thought to overfit the observations which led to
QM, and now these folk have made a prediction using waves of something
hereforeto unobserved, and have in fact observed the predicted behavior? In
that case I would say that the refinement of QM involving quantum waves has
been further shown to be consistent and in fact necessary to describe quantum
theory, not that quantum waves have been shown to be "real".

~~~
andrewcooke
it's not well explained, but i think it's about whether or not physical
theories with "hidden variables" are possible.

the idea is that maybe the uncertainty of quantum mechanics is a result of us
simply not understanding things right, and there's actually some deeper
"reality" (a better theory that we don't have yet) without the uncertainty.
<http://en.wikipedia.org/wiki/Hidden_variable_theory>

i thought this was already disproved (or it may be that hidden variable
theories can only work if physics is non-local? which is something people
don't like), but it's been years since i understood / tried to understand
this, and it's horribly subtle, so i guess there's more detail than i ever
knew...

~~~
sp332
Hidden variables are disproved by violations of Bell's Inequality.
[https://en.wikipedia.org/wiki/Bell_test_experiments#A_typica...](https://en.wikipedia.org/wiki/Bell_test_experiments#A_typical_CHSH_.28two-
channel.29_experiment) Basically, quantum systems are better (at certain
statistical correlations) than any classical system could be. The only
classical-ish explanation is transmitting information faster than light.

~~~
andrewcooke
ie non-local.

------
EvaPeron
This is exciting to me because it seems to make the Everett "Many Worlds" view
inevitable, because if A) the wave function exists (which this article seems
to indicate) and B) if it never collapses spontaneously (and 50 years of
research into this would seem to say no it does not), then necessarily one
gets "many worlds", i.e., a large number of co-existing universes inhabiting
an N-dimensional Hilbert Space, or, to put it differently, there are worlds in
which Schrodinger's cat lives, and ones where it does not.

All very cool, but I still am not planning to sign up for the quantum suicide
experiment to test for quantum immortality just yet. ;)

~~~
sp332
What do you mean by "never collapses spontaneously"? Researchers have been
trying to prevent states from collapsing for decades and it's really hard.

~~~
Symmetry
Under the Many Worlds Interpretation, the observations we could explain in
terms of waveform collapse are due to entanglement decoherence. The argument
for Many Worlds is that since our observations can be explained[1] in terms of
other well understood properties of quantum systems that we even have
equations defining, there's no need for this "waveforms collapse" hypothesis
that isn't even mathematically where we don't have any equations that tell us
when it occurs.

The idea, if you're not familiar with it, is that when a photon hits a partial
mirror part of the waveform goes one way and part goes another way. When
scientists conduct an observation of the photon they become entangled with it,
and similarly there are two sections to the scientist+photon waveform. But
because the mass of the waveform is now really humongous, you aren't going to
be able to observe quantum effects the way you do with a single photon.

[1] Except that alone doesn't tell us where Bode statistics come from.

~~~
madhadron
What are Bode statistics?

~~~
Symmetry
The fact that the likelihood of you seeing your instruments report a particle
in a given place is proportional to the square of the waveform's magnitude at
that place.

~~~
madhadron
Is that what it's called? I thought it was Jordan's rule.

------
pdx
I got turned off of this stuff in college. The whole probability wave business
has always smelled like smoke and mirrors to me. Schrodinger's cat has always
smelled to me as well ... especially a few days after the experiment, even if
I didn't open the box...

I like this Occam's razor approach. No more magic. There's a field there. We
don't yet understand it, but it's there, effecting things, and it's our job to
actually figure out what it is, not wave our hands about probabilities. This
feels real to me. The other interpretation did not.

~~~
madhadron
The hardest task of quantum mechanics is learning that the intuitions about
the universe baked into you by being human are wrong. You never actually
escape them, but you do learn to suppress the naive physics hardwired into
your brain and slowly and awkwardly simulate a better understanding using
another part of your brain.

------
guscost
Yes!!!

