

Measurements on the reality of the wavefunction - MichaelAO
http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3233.html

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TTPrograms
Every now and then people (on HN and elsewhere) like to rediscover pilot-wave
theory and other similar ideas that posit that billiard-ball-like-particles
still describe the universe. In these interpretations the wave-function, which
is the probabilistic field that modern physics uses to model particles, is
just an effective representation about our knowledge about the system. I tend
to see these theories as paying a price of drastic increase in complexity to
retain classical intuition about the system.

The mainstream view in modern physics (for the past 30 or so years, I believe)
is rather that the wavefunction is the fundamental description of reality, at
least in the sense that classical effective knowledge theories are not
plausible models.

My interpretation of this paper on quick glance is that it is an attempt to
experimentally demonstrate that only effective knowledge theories with very
strange properties would suffice to explain observations, thus strengthening
the "wave-function is fundamental" viewpoint.

~~~
phkahler
>> Every now and then people (on HN and elsewhere) like to rediscover pilot-
wave theory and other similar ideas that posit that billiard-ball-like-
particles still describe the universe.

Have you seen the experiments of Yves Couder?

Hypothetically, if a model like that produced an exact mathematical equivalent
of quantum theory wouldn't that be more satisfying? It would also destroy some
of the notions that have been mathematically proven - like EPR and Bells'
inequality. A lot of people are unsatisfied with QM and looking for something
more tangible - including physicists.

Apparently pilot wave theory was never soundly rejected, the crowd just went
in a different direction.

~~~
danbruc
_A lot of people are unsatisfied with QM and looking for something more
tangible - including physicists._

While I would also prefer that quantum mechanics turns out to be quite
classical at its heart - with objective reality, locality and all that - it
seems a pretty bad idea to expect or even assume that nature works the way we
prefer it to and that it will be easily understandable for human brains.
Actually, the longer we struggle to make sense of all of that, the more likely
it seems to me that everything is actually radically different from the way we
have looked at it for the past century.

------
cma
Full preprint article:

[http://arxiv.org/abs/1412.6213](http://arxiv.org/abs/1412.6213)

~~~
jriordan
Okay, I'm like 5 years old, but could you explain to me how this is available
here for free, yet it costs $32 to read the final published version?

I mean... this is fundamental human knowledge we are talking about... isn't
there some better way of doing this than $32-a-pop?

~~~
chriskanan
I have institutional access so I can't easily check, but I thought most or all
Nature journals were now freely available: [http://www.nature.com/news/nature-
promotes-read-only-sharing...](http://www.nature.com/news/nature-promotes-
read-only-sharing-by-subscribers-1.16460)

~~~
jsprogrammer
From the link you posted:

>All research papers from Nature will be made free to read in a proprietary
screen-view format that can be annotated but not copied, printed or
downloaded...

>Annette Thomas, chief executive of Macmillan Science and Education, says that
under the policy, subscribers can share any paper they have access to through
a link to a read-only version of the paper’s PDF that can be viewed through a
web browser.

The person who linked the original article didn't use the special link to the
"free, but proprietary" format.

------
tjradcliffe
The epistemic view of the wavefunction explains nothing, because it attempts
to put all the quantum weirdness into "our knowledge of reality" rather than
"reality".

The whole argument seems to me silly, because the epistemic view requires that
indistinguishable particles in fact are merely undistinguished particles. That
is, the epistemic view requires that reality behaves quantum mechanically when
no one _is_ looking at it, whereas what we observe is that reality behaves
quantum mechanically when no one _can_ look at it.

These are completely different situations. In one case it is what we _do_ know
that matters--which is an epistemic state--in the other it is what we _can_
know that matters, which is an ontic state. And it turns out that reality does
limit what we can know, and this has dramatic consequences.

The clearest example of this is the heat capacity of solids. Heat capacity is
a measure of how the temperature increases as you add heat energy to an
object. The temperature is just the average energy per state in the material,
so the heat capacity is a very direct measure of the number of states the
collection of particles constituting a material can be in.

It is very simple to show that particles that _cannot_ be distinguished have a
different number of states from particles that _can_ be distinguished even if
they don't happen to be at the moment. For example, consider two coins: if
they can be distinguished they have four possible states, HH, HT, TH and TT.
If they can't be distinguished then HT and TH are the same state (because
there is no way, even in principle, even if you're god) to distinguish the
left coin from the right coin. So there are only three states.

You can do something similar with particles in a crystal lattice and show that
they are indistinguishable. So it isn't a question of what we _do_ know, but
what we _can_ know, and that is determined by ontology, not epistemology.

The problem is that the ontology of the wavefunction is non-classical in the
extreme. Because it is nonlocal it violates the law of non-contradiction from
the perspective of locally causal beings (us). That makes it hard to
understand, but it doesn't make it any less real. It just means reality is
weird, which at this point in history shouldn't come as a huge surprise to
anyone.

~~~
FiatLuxDave
If you have not read Jayne's treatment of the Gibbs paradox, you may enjoy it.
He addresses exactly the question of what it means to say we cannot
distinguish particles from each other, and how 'cannot' really means 'cannot
with our current state of knowledge and tools (including known fields, forces,
etc).' See his analysis of two previously indistinguishable versions of Argon
which become distinguishable through new tools. I realize that this is in a
discussion of classical gas mixing physics, but the principle behind it is the
same. So, in short, epistimology does matter if our level of knowledge does
not exhaust the ontology.

Link:
[http://bayes.wustl.edu/etj/articles/gibbs.paradox.pdf](http://bayes.wustl.edu/etj/articles/gibbs.paradox.pdf)

