
Fluid Tests Hint at Concrete Quantum Reality - karolisd
http://www.simonsfoundation.org/quanta/20140624-fluid-tests-hint-at-concrete-quantum-reality/
======
GregBuchholz
I've liked:

Clearing up Mysteries - The Original Goal
[http://bayes.wustl.edu/etj/articles/cmystery.pdf](http://bayes.wustl.edu/etj/articles/cmystery.pdf)

" ...we must keep in mind that Einstein's thinking is always on the
ontological level; the purpose of the EPR argument was to show that the QM
state vector cannot be a representation of the "real physical situation" of a
system. Bohr had never claimed that it was, although his strange way of
expressing himself often led others to think that he was claiming this.

From his reply to EPR, we find that Bohr's position was like this:

"You may decide, of your own free will, which experiment to do. If you do
experiment E1 you will get result R1. If you do E2 you will get R2. Since it
is fundamentally impossible to do both on the same system, and the present
theory correctly predicts the results of either, how can you say that the
theory is incomplete? What more can one ask of a theory?"

While it is easy to understand and agree with this on the epistemological
level, the answer that I and many others would give is that we expect a
physical theory to do more than merely predict experimental results in the
manner of an empirical equation; we want to come down to Einstein's
ontological level and understand what is happening when an atom emits light,
when a spin enters a Stern-Gerlach magnet, etc. The Copenhagen theory, having
no answer to any question of the form: "What is really happening when - - -
?", forbids us to ask such questions and tries to persuade us that it is
philosophically naive to want to know what is happening. But I do want to
know, and I do not think this is naive; and so for me QM is not a physical
theory at all, only an empty mathematical shell in which a future theory may,
perhaps, be built."

~~~
abdullahkhalids
You are misrepresenting physicists. There have been many many different
attempts to talk about quantum theory on an ontological level. Case in point,
the widely debated interpretations: copenhagen, many worlds, bohemian etc.

However, one reason that physicists don't spend too much time thinking about
what quantum theory really means (besides laziness and bad science) is because
we know that quantum theory is not the ultimate theory of reality. Why try to
force ontology on a theory that can not even answer all empirical questions
without ad hoc additions (standard model of particle physics) or force mating
with another theory (general relativity)? We are all waiting for a better
theory of physics. Of course rewriting the quantum theory in different forms,
like this attempt, might help in getting there.

~~~
cabinpark
I agree and disagree with what you're saying. I agree it is laziness and bad
science that physicists stopped caring about the philosophical underpinnings
of quantum mechanics but I disagree that it was because quantum mechanics not
being the ultimate theory.

The reason most physicists don't think about the philosophical underpinnings
has more to do with the way quantum mechanics is taught. Many of the founders
were interested in the philosophical questions but after WWII you can see a
sharp decrease in that aspect and more of the hardcore calculation and the
philosophy kind of disappeared. Here [1] is a great talk that discusses this
very point. Unfortunate for quantum mechanics because understanding the
philosophical underpinnings is critical to understanding what quantum
mechanics says and doesn't say. But, thanks to things like quantum computing
and better experiments, interpretations is becoming more mainstream since
there are experiments being planned (at least when I was heavily involved in
the area in 2010) that would be able to test some of the claims made by
different interpretations.

>We are all waiting for a better theory of physics. Of course rewriting the
quantum theory in different forms, like this attempt, might help in getting
there.

To me this is a contradiction. If we are all waiting for a better theory, then
why are we re-writing the theory? A critical part of all the interpretations
I've encountered [2] is making different ontological claims about quantum
mechanics. Take Bohmian, which posits a guiding wave. Sure we can make some of
the mathematics nicer, but we can't go very far without explaining what this
'guiding wave' is, which itself is rather ad hoc. Plus, how do we rectify it
with Bell's theorem on hidden variables? To me, we can't really begin re-
writing quantum mechanics without inevitably running into ontological
statements.

But I still agree with your premise. I believe that by pushing the limits of
quantum mechanics both scientifically and philosophically we will get a better
grasp of what things to look for / where to look, for a deeper theory. Case in
point, wavefunction collapse. Some might consider it a huge problem of quantum
mechanics, but if you take a different ontological view, wavefunction collapse
isn't that interesting or important. So maybe wavefunction collapse isn't as
important and trying to develop a theory that doesn't have it is the wrong
idea.

[1] [http://pirsa.org/08090000/](http://pirsa.org/08090000/) [2]
[http://pirsa.org/C10002](http://pirsa.org/C10002)

~~~
thedufer
My understanding is that the pilot wave theory is a non-local hidden variable
theory, which doesn't contradict Bell's theorem at all. Of course, this
presents ftl information transfer, presumed to be impossible, which is part of
the reason such theories have been unpopular for so long.

~~~
danbruc
Non-locality does not imply the possibility of FTL information transfer - a
theory can be non-local but make exploiting the non-locality impossible.

~~~
adamgravitis
This is a vitally important point. Many people still naively believe
entanglement allows communication. Simultaneous randomness doesn't permit a
signal.

------
MichaelAO
FAQ about Bohmian Mechanics (it's very accessible):
[http://www.mathematik.uni-
muenchen.de/~bohmmech/BohmHome/fil...](http://www.mathematik.uni-
muenchen.de/~bohmmech/BohmHome/files/Frequently_Asked_Questions_about_Bohmian_Mechanics.pdf)

~~~
thedufer
Its certainly accessible, but I'm not sure how much I trust the authors to
understand what they're talking about after point 3.

> But very often the conclusion that is drawn from this observation is that
> our _knowledge_ about the path followed by the electron causes the
> interference pattern to disappear.

Although we couch the idea in terms of "knowledge", the usual meaning of that
word is not what anyone thinks is actually the trigger. What exactly is meant
by "knowledge" is not well-agreed upon, but no one thinks it is something
particular to humans (or sentient beings, I suppose) that causes the
wavefunction to collapse. It has more to do with whether the information
exists - if the particle interacts with something in such a way that its
position suddenly becomes deducible, then it collapses. Like I said, the
specifics of this are a known hole in the Copenhagen theory - but this
"knowledge" tangent is a clear strawman.

~~~
jostylr
That FAQ is generated by the students of a very trustworthy group. Students
typically setup strawman when explaining things. Look more to the source.
Also, they are trying to argue against a theory which no one wants to fully
specify. So they have to come up with something definite. And as soon as they
do, the other side says "Strawman!" And then proceeds, as you have just done,
to refuse to give a definite theory.

As a student of that group as well, I can't say that I am all that pleased by
that kind of argument.

The bottom line is that collapse is untenable. There is no good place to put
it and yet it is needed by the standard theory.

~~~
thedufer
There is a range of possibilities of what might cause a wavefunction collapse,
and the constructed strawman is nowhere near that. It would be like if we
claimed the speed of light was 3.2e8 +/\- 5e7 m/s and someone decided our
whole theory was bunk because the speed of light is obviously faster than 100
m/s. Well yeah, it is, but there's no contradiction here.

"if the particle interacts with something in such a way that its position
suddenly becomes deducible, then it collapses" would be a theory in the range
of possibilities. It would be much more convincing to argue against something
like that.

------
spacehome
Yes! But the best theory is not Copenhagen or Pilot Wave.

Eliezer Yudkowski has a brilliant treatise on the Many Worlds interpretation
here:
[http://lesswrong.com/lw/r5/the_quantum_physics_sequence/](http://lesswrong.com/lw/r5/the_quantum_physics_sequence/)
that really should be required reading for anyone that wants to talk
intelligently on the subject.

Edit: seriously, don't even bother reading the article. It (like most science
journalism) is garbage. Take the time to work through Eliezer's sequence.

~~~
acqq
So please explain in a few sentences what is that that Yudkowski writes, did
he make any new contribution to the standard model or made something else or
do you agree that the standard model is the most researched and most usable
model up to now, and he just made a lot of posts where he just writes a lot of
text?

I see a lot of links in the article you gave, but I don't understand what
we're supposed to discover in Yudkowski's writings after trying to follow most
of them. There's a lot of free text, not much physics. The standard model is a
lot of smart formulas supported by the decades of expensive elaborate
measurements (and vice versa), however his texts look more like writings of
some philosophy student who knows a little of the math than like a physicist's
material. I'd also really welcome opinions of professional physicists.

Edit: Wikipedia entry about him seems to fit my impression:
[http://en.wikipedia.org/wiki/Eliezer_Yudkowsky](http://en.wikipedia.org/wiki/Eliezer_Yudkowsky)
"Yudkowsky (...) is an American blogger, writer, and advocate for Friendly
artificial intelligence (...) Largely self-educated."

~~~
Sharlin
The Standard Model does not concern itself with the various interpretations of
quantum mechanics. It can, as of now, neither verify or falsify any of the
interpretations which, consequently, are not scientific theories or even
hypotheses, but firmly on the side of philosophy of physics. The
interpretations are attempts to answer _why_ Nature works as it does, _within_
the framework of the Standard Model which only appears to answer the question
_how_.

Yudkowsky certainly hasn't _invented_ the many worlds interpretation, which
was originally formulated by the physicist Hugh Everett in 1957. Even though
originally scorned, in the more recent times it has gained popularity among
physicists. The series of blog posts by Yudkowsky are (in my opinion, at
least) a persuasive argument in its favor against the competing
interpretations, and are very much recommended reading for anyone who would
like to better understand the issue.

~~~
acqq
> the interpretations which, consequently, are not scientific theories or even
> hypotheses, but firmly on the side of philosophy of physics.

Thanks, that's exactly what I wanted to know.

I'm completely satisfied with the "shut up and calculate" approach. For me,
until somebody shows that he/she can calculate (that is, predict) more than
what physicists achieve, they are the ones the closest to "the truth" and not
the "interpreter."

~~~
spacehome
Bring it back to the scientific method. The way to differentiate between
competing hypotheses is by devising experiments that falsify some of them, and
then running the experiments and either falsifying or failing to falsify them.

The issue here is subtle, and it's that the most popular interpretation,
Copenhagen, isn't a complete theory because it doesn't tell you
algorithmically when collapse occurs. For any possible algorithmic way to
handle collapse, there's a corresponding experiment that could (at least in
theory) differentiate between Copenhagen and Many Worlds. But the Copenhagen
is inordinately slippery in that collapse is defined to occur ex post facto in
whatever way is needed to make the experimental results match the theoretical
results.

It's perhaps not so surprising that this shortcoming was overlooked in the
beginning because Copenhagen was hypothesized before we really had a clear
handle on the study of algorithms. But the fact that Copenhagen is still as
popular as it is means that Yudkowski needs to spend a lot of time on
philosophy of science, because that's what's holding back most people from
seeing the problems with Copenhagen, and why at first glance it looks like
philosophy.

~~~
acqq
I think I can agree with your first paragraph, even if I'd phrase it somewhat
differently, but I don't see the connection between it and the next two.

~~~
spacehome
I certainly meant those three paragraphs to be connected; perhaps I'm just
poor at explaining. As I mentioned, the shortcomings of the Copenhagen
Interpretation are subtle, and I originally linked to Yudkowski's treatment
because I believe he does much better job of explaining it than I ever could.

~~~
acqq
Allow me to not agree with your classification of the top article as
"garbage." I've got from it more than from the text you linked to and I'm even
less satisfied with your explanations whereas Natalie Wolchover did a rather
good article. Please tell me if you have any background in physics, or what is
your background?

The major thing missing from the article for me is that she didn't mention
that the co-author of the most recent paper on the topic is much more known as
the security researcher than as somebody who does anything related to quantum
physics:

[http://arxiv.org/abs/1401.4356](http://arxiv.org/abs/1401.4356)

[http://en.wikipedia.org/wiki/Ross_J._Anderson](http://en.wikipedia.org/wiki/Ross_J._Anderson)

[http://www.cl.cam.ac.uk/~rja14/](http://www.cl.cam.ac.uk/~rja14/)

He's author of (to me) very useful book "Security Engineering":

[http://www.cl.cam.ac.uk/~rja14/book.html](http://www.cl.cam.ac.uk/~rja14/book.html)

------
nardi
Another anti-Copenhagen argument by Carver Mead:
[http://www.cns.caltech.edu/people/faculty/mead/Nature_Of_Lig...](http://www.cns.caltech.edu/people/faculty/mead/Nature_Of_Light_What_Are_Photons.pdf)

------
adocracy
Liquid dynamics sounds like an interesting hypothesis, but I agree with the
critics that entanglement presents a tough analogy. If Pilot Wave theory
suggests that the particle-wave duality is actually two distinct actors - a
wave and a particle riding the wave - then 1) each particle has an
independently generated wave? and 2) it's difficult to see how that wave could
be exactly preserved for both particles over the long distances of
entanglement experiments. That's like envisioning a ripple on the far side of
a large lake exactly mimicking a ripple here. Granted, the entanglement result
of simultaneous collapse of probabilities is also tough to rationally
understand. But Pilot Waves maintaining their effect, regardless of various
asynchronous interactions encountered between the distances of entanglement
experiments, seems naive. Then again, I'm not a particle physicist.

~~~
trhway
In interpretation of dual slit experiment people do the main mistake of mixing
up the 2 waves - one is wave like quantization of position and another is de
Broglie wave-equivalent of the particle. The mix up is caused by photon where
both have the same wavelength. They are different in the case of all other
particles. Hitachi experiment shows its the best - it clearly shows
interference of the positional waves of different particles, not the de
Brogile wave (ie. not the particles themselves). It thus also lends very
credible support to statistical ensemble interpretation (which, as far as i
know, Einstein favored)

People frequently bring up single-particle self-interference as explanation
for Hitachi too. Well, in case of photon the self-interference pattern looks
the same as positional interference because of the same wavelength. In case of
electron and especially neutron the self-interference pattern would be much
more dense than observed one because of the much higher de Brogile frequency
than the frequency of the positional quantization.

The wave-like quantization of position is the Pivot Wave. The really important
thing here is to understand that Pivot Wave isn't a real wave/object. It is
just a description of possible positions of the particle at specific times.
Like a trajectory of a bullet isn't a real thing, it is just description of
possible positions of the bullet at specific times. It is just in QM the
trajectories are wave-like quantized and probabilistically spread - that the
non-smooth at small scales structure of our Universe shows its "ugly" face :)

Again, taking the quantized wave-like trajectory description of a particle for
a real thing, the particle itself, is the main misinterpretation that has been
going for years, especially in Copenghagen interpretation.

~~~
phkahler
>>The really important thing here is to understand that Pilot Wave isn't a
real wave/object. It is just a description of possible positions of the
particle at specific times.

Is it possible that pilot waves are ripples in space-time? We should not make
strong assertions especially when a theory is young. You make it sound like
nothing more than the a regular QM wave function.

~~~
danbruc
Ripples in space-time are gravitational waves. It could be a real wave but the
danger is that one introduces a preferred references frame. Not that it would
be the end of physics but it would surely be a big surprise.

------
dnautics
I was under the impression that Bohmian mechanics were known to be equivalent
if and only if hidden variables were strictly non-local (in the case of the
macrophysical observations, the "universe" can for a reasonable higher-order
approximation be the limits of the chamber being observed).

IIRC, There is also an interesting 'alternative' relativity which has non-
local effects and a universal frame of reference formulated by a physicist
named Frank Tangherlini (I'll be interviewing him this month). It also has
weird properties like anisotropy of the vacuum speed of light!!

Might be interesting if Bohmian and Tangherlini mechanics provided a better
mathematical rapprochement of quantum mechanics with relativity than
Copenhagen/Lorentz/Einstein

~~~
pdonis
_I was under the impression that Bohmian mechanics were known to be equivalent
if and only if hidden variables were strictly non-local_

Correct. The same is true of Bell's theorem; it shows that no local hidden
variable theory can reproduce the predictions of standard quantum mechanics.
It's true that the "local" part often gets left out in pop science treatments
of Bell's theorem; but Bell himself was quite clear about it, and about the
fact that Bohm's pilot wave theory is nonlocal. The article completely fails
to mention this, which IMO is a huge omission.

------
vitamen
This sums up my thoughts exactly. The pilot-wave theory "...seems to me so
natural and simple, to resolve the wave-particle dilemma in such a clear and
ordinary way, that it is a great mystery to me that it was so generally
ignored."

I don't run in experimental-physicist circles, granted, but I've definitely
encountered countless cases of a clear, obvious, correct solution being
brought up and summarily ignored for what proves to be a poor solution. The
probabilistic theories have always made for good Science Fiction, but that
should hardly matter.

~~~
mpweiher
This seems to be common problem. Watzlawick describes an experiment where two
people (A and B) are given the task to classify tissue samples as "healthy" or
"sick".

There is an initial training session where a light tells them whether their
answer was correct, with one little caveat: only A gets real feedback. B's
light just duplicates A's, so the answers that B receives are essentially
random (I think they get different picture as well).

Since the task is not very difficult (on purpose), the As learn the task in
80% of the cases. The Bs have a much more difficult task, they are required to
try and find order in a random world. They form _very_ complex theories to
account for this.

However, that's not the experiment quite yet. The real experiment is that As
and Bs are then put together to discuss their results. What happens then is
stunning: instead of rejecting the B's theories as unnecessarily complex, the
As are usually so impressed with the subtle complexity and detailed brilliance
of the B's theories, that they change their mind and accept the B theories!

When asked who will improve in the next round, all the Bs and most of the As
pick the Bs. And they are right, because the As will have accepted at least
some of the Bs ideas and thus perform more poorly.

Reference:
[http://omg.pytalhost.net/dls/ebk_wwidw.pdf](http://omg.pytalhost.net/dls/ebk_wwidw.pdf)
(German)

------
jamestomasino
By far the most fantastic and unbelievable part of this article is the calm
thoughtfulness and collaborative criticism in its comments. Thank you, OP, for
sharing such a rare gem.

------
hcarvalhoalves
I'm impressed by the probability distribution graph in the video. I would
never expect the random motion to form a wave!

~~~
gfodor
that's the point, it's chaotic, not random.

------
bitwize
Interesting. Maybe this will discourage chuckleheads and ne'er-do-wells from
citing "quantum physics" as the justifixation for their particular variety of
woo?

Probably not, but one can hope!

~~~
ben0x539
If you can't bullshit your way through criticism with vague-sounding phrases
like “As the particles move along, they feel the wave field generated by them
in the past and all other particles in the past”, you're not trying hard
enough. :v

This magical bracelet is powered by the wave field shaping the contours of the
superfluid of space time! Carrying you through life on positive pilot waves!

~~~
voyou
I can imagine supporters of homeopathy would have a great time drawing
unfounded conclusions from the bit in that article that talks about fluids
exhibiting a "path memory".

~~~
thibauts
Would be even worse if it was proven that molecule actually have this kind of
memory.

------
sriku
If you try to create a classical situation that obeys similar mathematics to a
quantum situation, you're bound to get "quantum-like behaviour" isn't it?
Wouldn't this be some kind of an analog computer for simulating the two-slit
experiment in the classical realm? If so, what would this offer to the
interpretation of quantum mechanics that cannot be gleaned from the
mathematics itself?

~~~
msane
The significance is that this is a model of a special, alternate formulation
of quantum mechanics called Pilot-wave Theory.

~~~
sriku
pwt is an interpretation. All interpretations of QM share the same mathematics
.. or effectively the same maths. Different "interpretations" cannot produce
different predictions in experiments. So using an experiment designed to
emulate pwt (which afaik violates special relativity) can only say one thing
possibly - that if we find it convenient to think in this way in some limited
cases of quantum mechanics, we may do so. In other words, it may at best serve
as a heuristic to teach children, that they can later grow out of.

~~~
msane
> All interpretations of QM share the same mathematics .. or effectively the
> same maths.

No they do not.

> Different "interpretations" cannot produce different predictions in
> experiments.

Yes they do.

------
DavidPlumpton
I was unable to figure out one key thing about this article. Are they claiming
that if the droplet is observed while going through one of the slits that the
interference pattern will vanish? If not can we really claim a strong analogy
with QM?

~~~
ars
Yes.

"And just as measuring the trajectories of particles seems to “collapse” their
simultaneous realities, disturbing the pilot wave in the bouncing-droplet
experiment destroys the interference pattern."

------
pistle
Excellent. Hope this gets support and more attention. I'm getting tired of
explaining how hand-waving about probabilistic magic of subatomic behavior is
successful guessing of reality without explaining it.

------
mrfusion
Any ideas on how quantum computing would be explained with this model?

If quantum behavior is really classical like I think they're claiming,
wouldn't that mean quantum computers wouldn't provide any benefit?

~~~
rrss1122
I'm not sure how quantum computing would be explained, but if it is classical
then yes, quantum computers really wouldn't provide any benefit. This brings
to mind headlines recently on how so-called quantum computers could not
outperform optimized classical computers on algorithms specifically designed
to cater to a quantum computer's strengths. Of course, then you would have to
argue whether there actually are any quantum computers in existence today, or
the quantum computers that are claimed to exist are actually classical
computers exploiting some quantum effects.

~~~
lfuller
The D-Wave devices that you are referencing are actually quantum annealing
machines, not universal quantum computers. A quantum annealing machine is to a
universal quantum computer what a mechanical computer is to a digital
processor.

------
Estragon
Are there any experiments where the pilot wave theory and the Copenhagen
interpretation predict different results?

~~~
tim333
It depends a bit how you define things. The Copenhagen interpretation has a
collapsing wave function doing so in a way where we can't observe it collapse
and the pilot wave theory has pilot waves all over the place that have no
effect other than guiding the particle in question then effectively
disappearing when not needed. If either the collapses or pilot waves were real
things I would kind of expect them to be observable in some way, but in both
interpretations they are not observable, which leads me to suspect they are
not real things and will go the way of the "luminiferous aether".

~~~
jostylr
Funny that you say that since the particles are pretty much all we do observe.
You never "see" the wave function, but you do see where stuff is.

To be charitable to Copenhagen, we would say that we do see the results of
collapse. The main problem with the collapse is that is simply not well-
specified by the theory.

------
stefantalpalaru
I would not be surprised if it turns out that the Copenhagen interpretation is
a modern phlogiston theory.

------
dang
We changed the url from [http://www.wired.com/2014/06/the-new-quantum-
reality](http://www.wired.com/2014/06/the-new-quantum-reality) to be the
original source.

~~~
ars
Thanks, because that is a really well written article so I added that magazine
to my RSS.

