
Have We Been Interpreting Quantum Mechanics Wrong This Whole Time? - brg
http://www.wired.com/2014/06/the-new-quantum-reality/
======
tjradcliffe
The difficulty with these semi-classical interpretations of quantum phenomena
is that they tend to work nicely for a few very simple cases and fall to bits
when things get more complex. Bohm's quantum potential works almost perfectly
for single electron atoms, in which the quantum potential simply holds the
electron still, but falls apart for multi-electron atoms, which require a
higher dimensional space for the quantum potential to live.

Although Bell did defend pilot wave theory--which is taught in every
introductory QM course and covered in every introductory QM text--he himself
did not see it as anything more than an inspiration for a more complete
interpretation, which would necessarily be non-local in accordance with the
theorem that bears his name.

My own belief is that pilot waves cannot account for quantum statistics, and
therefore cannot account for the heat capacity of solids:
[http://www.tjradcliffe.com/?p=470](http://www.tjradcliffe.com/?p=470) There
is a claim that pilot wave theory somehow deals with this, but the argument is
focused on the decay of radioactive particles rather than thermodynamics,
which seems to be odd, because the thermodynamic argument is the fundamental
one: the heat capacity of solids is an unequivocal way of counting available
states, and if hidden variables (such as the "true" positions and momenta of
the piloted particles) exist then they break the symmetry under exchange that
gives rise to the statistics we observe, and create additional states that
would... hmmm...

OK, having thought about it for a bit I'm no longer _entirely_ convinced it's
impossible that pilot waves might preserve the symmetry while also preserving
identity. It would require that exchanging the labels on the pilot waves
precisely compensate for the labels on the particles. Would that be enough?
I'm going to have to think more about this before forming a more firmly held
opinion on it.

~~~
jessriedel
> ...pilot wave theory--which is taught in every introductory QM course and
> covered in every introductory QM text...

Having assisted in teaching intro QM courses, I can say this is very incorrect
-- unless you replace "every" with "many" and "taught/covered" with "mentioned
off hand".

I just pulled the very popular "introduction to quantum mechanics" by
Griffiths off my shelf. It contains nothing about pilot waves except for a
single footnote in an appendix used as an example of "a number of hidden
variable theories [proposed over the years]".

~~~
tjradcliffe
OK, "every GOOD intro QM course" and "every GOOD intro QM text" :-)

I shall now walk away mumbling about the degenerate state of today's youth...

~~~
Osmium
Griffiths happens to be the most accessible while-still-rigorous QM book I've
read, so I'd be careful with the criticism ;) it is concise though, which is
probably the main reason it doesn't really discuss pilot waves.

------
amluto
I think that these oil droplet experiments are incredibly neat, but I'm
surprised by the conclusions about the universe that people try to draw from
them.

There are fascinating lab experiments related to black holes [1]. Researchers
have figured out how to build things in the lab that obey some laws that are
mathematically very similar to those that we think that black holes obey.
These black hole analogues end up doing similar things to what we expect real
black holes to do.

Nonetheless, no one seems to see those experiments and conclude that "Wow! Our
universe must contain black holes that emit Hawking radiation!".

These oil droplet experiments do something quite similar. They create an
environment that is reasonably well described by the same equations as pilot
waves, and, since those equations are known to make the same predictions as
quantum mechanics, the oil droplets do the things that we would imagine
quantum particles to do.

This may be beautiful, but just as the existence of black hole analogues in
the laboratory does not imply that black holes are real, the existence of
pilot-wave-following oil droplets does not imply that pilot waves are better
than quantum mechanics.

[1]
[http://www.nature.com/nphys/journal/v10/n11/full/nphys3104.h...](http://www.nature.com/nphys/journal/v10/n11/full/nphys3104.html)

~~~
eli_gottlieb
Pretty much everyone actually thinks black holes are real.

IANAP.

~~~
yzzxy
I think he was referring to Hawking radiation - which is far more
controversial in physics circles and a major WTF idea for non-physicists - and
other theoretical black-hole behavior, not existence of black holes
themselves.

------
lisper
The "smoking gun" quote:

"Yet an experimental test of droplet entanglement remains a distant goal."

And it will remain a distant goal forever. Per Bell's theorem, entanglement is
inherently non-local. Bohmian pilot waves are also non-local, so they can
reproduce all the results of QM, but no purely classical model can.

------
emhs
Somehow, even though Collapse is insane if you think about it hard enough, and
even though Pilot-waves are semi-classical and seem to be adding an additional
complication that may not be necessary, both of these seem to be more popular
among physicists than Many-Worlds. Somehow, even though superposition is
observed and observable, even though the scale on which we can observe it is
climbing steadily larger, people keep assuming that it either dissipates
sometime before our scale, or that it's an illusion produced by some sort of
semi-classical, overcomplicated reinterpretation.

The original idea—that the wave function is the whole deal—works just fine if
you accept that _we_ can be in superposition too. If you simply accept that
the _entire_ classical concept might be an illusion, and work up from the wave
function, there's no reason to shoehorn in an idea like Collapse or Pilot-
Wave.

Yes, Copenhagen is wrong. Yes, Collapse is patently absurd. Yes, assuming that
there is exactly one, stochastic, probabilistic reality makes no sense. But
that doesn't mean we need to add something complicated like an underlying
superfluid that supports all of spacetime. This smells like Aether.

 _Why does no one talk about Many-Worlds?_

~~~
tjradcliffe
I agree with the comment regarding the Born Rule, which is indeed a deep
objection.

A further objection is aimed ad the claim that "we can be in a superposition"
and it is: "If we can be in a superposition, why aren't we aware of it?"

This is a general question that any interpretation of QM must answer, and none
does, which comes down to: "Why is there a classical world at all?"

There is a sense in which every interpretation of QM is an attempt to answer
this question, but none do.

Decoherence, for example, simply asserts that we cannot be aware of quantum
effects except via interference phenomena. Why not? Why can't we be _directly
conscious_ of the various incoherent components of the wavefunction in the
same sense of _directly_ that I am _directly conscious_ of my cat sitting
beside me? [1] I don't have to do any fancy interferometry or statistical
inference to be aware of the cat, so why do I have to mess about with
statistics and interferometry to be aware of the wavefunction, given I myself
am described by one?

The fact that my multiple incoherent states do not interfere with each other
is irrelevant unless you have some reason to believe that it is only via
coherent interactions (interferecne patterns) that the wavefunction manifests
itself to consciousness, and why would that be?

When I measure a gamma decay why am I aware of an event at a moment in time
rather than a continuous probability wave? Likewise, why can't I be conscious
of the wholistic universe that Many Worlds implies?

I've focused on consciousness here because there is no doubt we are directly
aware of the classical world but are only indirectly aware of the quantum
world, but there is very little reason to believe there is anything
particularly special about consciousness in this regard. More likely, the
brain, body, planet, etc, all "partake in" classical physics, none of which
makes any sense from a quantum perspective.

That is: if all you knew about was quantum mechanics, you would never come up
with Born's Rule or anything like it because you would never have any reason
to talk about the results of classical measurement. You would not be aware
than anything like classical measurement could exist.

So if we believe that QM is somehow foundational or fundamental to the
classical world (and who doesn't?) then the fact that it gives no indication
that the classical world even exists is something of a problem.

[1] To belabour the point: I do not mean "direct" in any Cartesian sense, but
simply that there is a perfectly ordinary causal relationship between my cat
and my awareness of my cat, which is quite different from my awareness of
wavefunctions, which can only be via indirect means. We might have any number
of additional senses, but all of them would be direct in this sense: none of
them would allow me the immediate, simultaneous perception of a photon
travelling through both slits at once. As Feynman said: this is the
fundamental mystery.

~~~
lmm
> A further objection is aimed ad the claim that "we can be in a
> superposition" and it is: "If we can be in a superposition, why aren't we
> aware of it?"

Sounds rather like the fish being unaware of water. What would _not_ being in
a superposition feel like?

> Decoherence, for example, simply asserts that we cannot be aware of quantum
> effects except via interference phenomena. Why not? Why can't we be directly
> conscious of the various incoherent components of the wavefunction in the
> same sense of directly that I am directly conscious of my cat sitting beside
> me? [1] I don't have to do any fancy interferometry or statistical inference
> to be aware of the cat, so why do I have to mess about with statistics and
> interferometry to be aware of the wavefunction, given I myself am described
> by one?

So "you" is a quantum computer or something behaving like one, right? For you
to "be aware of" a wavefunction, you'd have to causally interact with it. And
that's very hard because of e.g. the no-cloning theorem; all you can do is
entangle a qbit in your head with the qbit you're trying to measure, but what
does that actually get you? What does that subjectively feel like? What
operation would you expect to be able to perform that you can't?

------
Animats
If this leads to an experimentally verifiable prediction different from the
current view of quantum mechanics, it's a very big deal. Otherwise, it's not.

------
jaekwon
Pilot wave resonance/nonresonance from the two receivers of a Bell's
inequality experiment may affect the behavior at the source leading to a kind
of Monty Hall problem observed as QM. Are we certainly capable of firing a
singular entangled photon on command at the press of a button regardless of
the orientation of the receivers, or does the firing ability of the source
emitter seem to falter with orthogonality at the end receivers?

Of course this could be complicated by a mechanism at the source that ensures
a single pair to be emitted. Imagine a mechanism that ensures that only one
pair is produced, but it is produced eventually, like a for-loop with a break
statement. And maybe the only way to conduct the Bell's Inequality experiment
meaningfully is with such a throttling mechanism, which would mask the answer
to the question above. Though there might be hints in the amount of time
required to generate that singular pair, as if the for-loop had to run more
iterations before it was produced, detected only with sensitive timing
instruments like with side-channel timing attacks in cryptographic black
boxes.

------
calhoun137
I would characterize these fluid dynamics experiments as "very cute", but
nothing more.

One of the sad things about physics these days is that it has become more like
religion in a bad way. I first heard about Bohmenian mechanics, which this
article is about, 8 years ago. I never believed in it, and always thought it
was silly. I say "believe" because at this point it really is a question of
faith.

It was amusing to me to read this article, it makes all the same points I used
to argue against but in a very clever and well written way. What the
Bohmeanian mechanics people used to say was the only reason they couldn't
respond to this or that problem with the theory was "not enough people were
working on it".

From the article:

"Some researchers said that [Bohmean Mechanics] has trouble dealing with
identical particles, and that it becomes unwieldy when describing
multiparticle interactions. They also claimed that it combines less elegantly
with special relativity. But other specialists in quantum mechanics disagreed
or _said the approach is simply under-researched._ "

~~~
SpaceManNabs
Every time I hear people say that physics has become has become a religion I
want to stab myself. Every day, I sit at Peyton Hall at Princeton and
discussions at the IAS where people are consistently debated. There is nothing
dogmatic. If you are wrong, you will get corrected. See BICEP2.

~~~
TheOtherHobbes
"Bohmian mechanics has never been widely accepted in the mainstream of the
physics community. Since it is not part of the standard physics curriculum,
many physicists—probably the majority—are simply unfamiliar with the theory
and how it works. _Sometimes the theory is rejected without explicit
discussion of reasons for rejection. One also finds objections that are based
on simple misunderstandings;_ among these are claims that some no-go theorem,
such as von Neumann's theorem, the Kochen-Specker theorem, or Bell's theorem,
shows that the theory cannot work. Such objections will not be dealt with
here, as the reply to them will be obvious to those who understand the theory.
In what follows only objections that are not based on elementary
misunderstandings will be discussed."

[http://plato.stanford.edu/entries/qm-
bohm/#o](http://plato.stanford.edu/entries/qm-bohm/#o)

It's true that Bohmian mechanics has never been extended to a full QFT. But
considering how little time has been spent on it, isn't it possible this is a
result of observed bias against it, and not because it's fundamentally
intractable?

For comparison, other theories that have ended up in more intractable places
(such as string theory) seem to be considered mainstream.

------
msravi
Any sufficiently complex system that has a sufficiently large number of
known/unknown parameters whose interactions are unknown/partially known/not
measurable appears random.

For example, while the path of a piece of paper as it drops to the ground can
be modeled exactly based on several parameters such as gravity, air currents
(and its parameters), etc. the number of parameters are so large and their
interactions so complex, that the only useful approach is to model it
statistically. The same goes for the weather. Or the economy. Or the stock
market.

It appears that the current quantum mechanical view of the world is simply an
acknowledgement of this complexity and the associated unknowns. While it
presents a statistical "model" that works for our purposes, it must be
acknowledged as a model and not confused with reality. The push for figuring
out what drives the statistics needs to continue beyond the building of a
model.

~~~
Rapzid
I noticed a few of the quotes in the article from physicists who, while not
outright dismissive, couldn't be bothered about pursuing something that could
lead to a more fundamental understanding of reality.

~~~
scottlocklin
Unfortunately this was written by a science reporter, and so, it was written
with an angle by someone who doesn't know what he is talking about. Their
dismissiveness is well justified.

I was a big fan of exploring the alternative ideas in quantum mechanics, and I
tried to like Bohmian pilot waves. They are very philosophically appealing.
Then I saw some results in quantum optics which pretty much convinced me it
was a silly idea. Walther's ideas on Surrealistic Bohm trajectories should
have been enough. I'd be curious if these oil droplets exhibit the
surrealistic trajectory behavior. It would be neat if they did, but I doubt
it.

While the fluid mechanical experiments are pretty damn neat, the modern
revival of Bohmian mechanics is a symptom of the disease that afflicts today's
physics community: there are many people who call themselves physicists who
insist on working on things which have no physical consequences. If you can't
do an experiment, you're a philosopher, armed with math. People who claim they
might be able to make an experiment in 20-40 years (after they have tenure and
have retired) are arguably worse: yes, I am looking at you, entire field of
quantum information snake oil salesman: build something or shut up. All this
is a sign of decadence and decay, and it is extremely sad to see so many
clever people being so stupid.

FWIIW, I was exposed to Bohm mechanics in my junior year QM course; it's not
like nobody has heard of it. It is actually quite ubiquitous in certain kinds
of gutter popular literature; the kinds of popular QM books people who believe
in psychic powers read. I've met strippers in gothic nightclubs who knew who
David Bohm is. As in, more than one.

------
espitia
Although I read the article, I really don't understand much the theories and
technicality of it. What has fascinated me for a while is the slit experiment.
What I tie this to is the Law of Attraction. Say that the subconsciousness is
the connection from ourselves to the universe (via meditation for example),
what if this is the way for us, through our thoughts, to "observe" what is
going to happen (in other words, what we want to happen) and therefore the
universe "brings" it to us simply because we observed it? Thanks to having
some sort of logic I can believe in, I use the law of attraction and it has
proven to always bring me what I want in life so far :)

~~~
inclemnet
It's vastly more plausible that your brain is good at seeing patterns where
none exist than that you have psychic powers.

------
mkempe
Here are Yves Couder's 2011 slides with more details, graphs, photos, and
references. [1]

I have a general question for those who are expert in physics, or who have a
hobbyist interest: have you read Louis de Broglie's "Ondes et mouvement"
(1926)? it's only 133 pages in the original French edition. Or his 1924 PhD
thesis? [2]

[1]
[http://www.physics.utoronto.ca/~colloq/Talk2011_Couder/Coude...](http://www.physics.utoronto.ca/~colloq/Talk2011_Couder/Couder.pdf)

[2] [https://tel.archives-
ouvertes.fr/tel-00006807/document](https://tel.archives-
ouvertes.fr/tel-00006807/document)

------
officialjunk
here's there original research:
[http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108...](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.264503)

an article about this gets published about once a year. here's the first one i
encountered:
[http://physicsworld.com/cws/article/news/2012/jul/09/bouncin...](http://physicsworld.com/cws/article/news/2012/jul/09/bouncing-
droplets-simulate-zeeman-effect)

------
boardstretcher
Title is confusing. Correct me if I'm wrong, but Quantum Mechanics _is_ the
interpretation of the very small, so the title is essentially 'Have we been
interpreting the interpretation wrong this whole time?'

~~~
inclemnet
Quantum mechanics in this sense refers to the (very well researched and
understood) mathematical theory. This theory permits multiple philosophical
explanations of what is 'really happening' to give the mathematical results
that we confirm to be correct in experiments.

Any debate about the interpretation of quantum mechanics refers to to this
question of what really happens, not to any details of what QM actually
predicts will happen. That is, until/unless experiments are devised to
separate these philosophical explanations, but nothing much has happened on
this front for decades.

~~~
boardstretcher
Great explanation. Thanks for clearing that up so succinctly.

------
dsugarman
I am not a quantum physicist, can anyone explain what implications (if any) a
deterministic model of quantum mechanics would have on the potential of
quantum computing?

~~~
one-more-minute
I think the idea of this interpretation is specifically _not_ to have any
implications outside of what we already know. They should be equivalent in the
sense that you can derive one from the other.

It's like making Newtonian mechanical predictions based on F=ma vs. energy
arguments, or analysing computation using a Turing machine vs. lambda
calculus. The theory can't fundamentally change but you can use a different
conceptual framework to get the same results (and some may be much easier to
work with / more intuitive than others).

------
ThomPete
I think the whole problem of interpreting quantum mechanics and classical
physics is that from what we can see it's counter intuitive and anti-narrative
i.e. it cannot be expressed philosophically/via language in any meaningful
way.

Mathematically it makes sense, experimentally it makes sense, it is as proven
as classical physics are proven yet the two contradict each other.

Perhaps it is as the old zen-buddhist saying go. Wisdom lies in paradox.

------
nsxwolf
No. Yes.

~~~
chm
I would say:

P = 1/Sqrt[2] (Yes + No).

~~~
lisper
|YES>|NO>

