There exists a classical model of the photon after all

https://www.lightbluetouchpaper.org/2015/02/23/maxwell/

by inglesp • 11 years ago

170 84 11 years ago

cevn• 11 years ago

"Updating this with modern knowledge of quantised magnetic flux, we show that if you model a flux tube as a phase vortex in an inviscid compressible fluid, then wavepackets sent down this vortex obey Maxwell’s equations to first order; that they can have linear or circular polarisation; and that the correlation measured between the polarisation of two cogenerated wavepackets is exactly the same as is predicted by quantum mechanics and measured in the Bell tests."

How long would I have to study physics to be able to understand everything in this sentence?

fdej• 11 years ago

You should be able to understand everything in that sentence if you have taken a typical undergraduate curriculum in physics including quantum mechanics and electromagnetism. Though it depends on what you mean by "understand". It should be clear what "quantised magnetic flux" is roughly about, but I have no idea what constitutes the "modern knowledge of quantised magnetic flux" in this context.

sp3325• 11 years ago

That doesn't help with the first part, about a phase vortex in compressible inviscous liquids.

dkarapetyan• 11 years ago

A lifetime, or long enough that it would feel like a lifetime. The real question to ask is that how you really want to spend your life? The fact that you're asking makes me think you've already chosen another path.

maaku3• 11 years ago

It does not take a lifetime. It took me about 6 months to cover upper-division electricity and magnetism and quantum mechanics, which is probably all that you would need to get the most basic but complete understanding of this paper.

Iftheshoefits• 11 years ago

Just about every concept (mathematical and physics) in the arXiv paper linked from the article is covered by the end of a typical undergraduate course in electromagnetism and quantum mechanics. The ones that aren't (specifically with respect to certain particulars of fluid dynamics and flux) are easily supplemented with material of the same depth and complexity (i.e. undergraduate level).

jerf• 11 years ago

To really, really get it? The standard electromagnetism semester and a QM semester, both "for majors" (not the simplified general version), and something else for the "inviscid compressible fluid" (fluid dynamics, I assume, this might require some stuff that won't come up until semester 2, not sure), and a factor difficult to express in terms of semesters that you are not merely aping the mathematical results you are being taught by rote, but actually understand how to manipulate the math and follow deeply when you see other people do it. (Which I mean quite straight, not sarcastically.)

I'm pretty sure this would all be accessible to an undergrad physics major who passes my math criterion above. It would probably be beyond them to do the work, but they should be able to follow it.

rayiner• 11 years ago

An aerospace major who took a QM elective, or a physics major who took a couple of aerodynamics electives, would probably cover the necessary material by the end of year 2 of an undergraduate program. If you've got a solid, intuitive grasp of calculus and differential equations, you could probably learn enough from lecture notes to understand this in a few weeks. This is the most accessible physics paper that you'll ever see make the news.

clavalle2• 11 years ago

It can take a bit of unpacking, but someone with some sort of college level physics and mathematics background can use Wikipedia to get a basic understanding of what they are talking about.

They are basically saying that the quantum mechanical 'strangeness' of light can be explained with classical, deterministic, physics. It is not necessary to have a separation in which quantum mechanics predominates at one level and trumps classical mechanics.

It call all be understood as movement of 'particles' of light (photons) on an underlying wave.

http://en.wikipedia.org/wiki/Magnetic_flux_quantum

http://simple.wikipedia.org/wiki/Magnetic_flux

http://en.wikipedia.org/wiki/Flux_tube

http://en.wikipedia.org/wiki/Quantum_vortex

http://en.wikipedia.org/wiki/Wave_packet

http://en.wikipedia.org/wiki/Maxwell%27s_equations

http://en.wikipedia.org/wiki/Differential_equation

http://en.wikipedia.org/wiki/Polarization_%28waves%29

http://en.wikipedia.org/wiki/Bell_test_experiments

http://en.wikipedia.org/wiki/Fluid_dynamics

http://en.wikipedia.org/wiki/Pilot_wave

http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory

itistoday2• 11 years ago

Pilot wave theory has been known for decades. So can someone explain how whatever they're talking about is different/new?

sampo3• 11 years ago

How long would I have to study physics to be able to understand everything in this sentence?

Just start reading David J. Griffiths: Introduction to Electrodynamics. A very well written textbook. The problem might be, if you don't know vector calculus, you might not be able to read this book, so you need to learn some vector calculus, too.

Then start reading Introduction to Quantum Mechanics by Griffiths, too. Best introductory QM book that I know of. If you managed to read Electrodynamics, you should by now know enough calculus for this book, too. But you also need to know about complex numbers here.

The "inviscid compressible fluid" is about fluid mechanics. I don't know any splendid textbook on that.

nilkn4• 11 years ago

I haven't read it, and it may be too advanced for this purpose, but Landau's books are generally held in extremely high regard and volume six of his Course of Theoretical Physics is on fluid mechanics.

For what it's worth, volumes two and three cover electrodynamics and quantum mechanics, respectively.

projectileboy• 11 years ago

Wow, so nice to hear props for Griffiths' textbooks. I think he's by far the best physics textbook author.

mbq• 11 years ago

For superfluid mechanics (which they seem to be using as a foundation) Donnelly's "Quantized Vortices in Helium II"'s introduction is a pretty good start. The field is quite hermetic, though.

tallon• 11 years ago

I disagree with the suggestion of Griffith's QM. Somehow, Griffiths made an excellent EM book, but terrible QM. I find Shankar's Principles of Quantum Mechanics to be much more comprehensive and easy to follow.

angdis• 11 years ago

It depends on what you mean by "understand everything". That is a very terse, densely packed sentence of jargon intended for practitioners but a physicist who is a skilled communicator could describe the main results to a high school kid. To be able to fully understand the arguments leading to those results... it would take very serious study and decently sophisticated mathematical background before even starting.

phkahler5• 11 years ago

I hope this is as awesome as it sounds. It sums up everything I've been thinking about quantum physics, from "someone should look closer at Couders work" to "spooky action at a distance is BS" to "Quantum computers will never work - see spooky action".

lisper• 11 years ago

I hope this is as awesome as it sounds.

If it's true, it would be even more awesome than it sounds. It would be the biggest breakthrough in physics in 100 years. I'll give you long odds against it turning out to be true, but I won't bet my entire life savings on it.

[EDIT] I have now read the paper and I'm ready to bet my life savings that it's bogus. There's just nothing new here, just a hand-wavy argument that classical mechanics can violate the Bell inequalities because "lines of force." It's possible that QM will be overturned some day, but when it happens it won't look like this.

phkahler5• 11 years ago

Yeah, I don't like when they say it matches XXX to first order... Does it match or not? OTOH it suggests that another model might, just like Couder suggested.

maaku3• 11 years ago

Reasoning from intuition has a terrible track record, I'm afraid.

UhUhUhUh• 11 years ago

Really? Did Einstein have empirical proof of his ideas?

sp3325• 11 years ago

Spooky action has been empirically demonstrated. https://arstechnica.com/science/2012/04/decision-to-entangle...

phkahler5• 11 years ago

I call BS. If that's true, then Victor can not only send information across a distance, but back in time. Victor is changing the correlation of Alice and Bobs measurements after they have already been made. That's going to need serious verification for me to accept.

pbhjpbhj2• 11 years ago

It's quite exciting to see these sorts of papers.

What fascinates me is that we have achieved so much in the "quantum age" of the past century using the models derived from a quantum mechanical approach to physics. That the bedrock [or lack of one] of that could be removed and provide a better, more consistent, approach seems so counter-intuitive. But then one recalls how long the Newtonian or Aristotelian approaches [or any other such system] stood.

Also would this be a return to universal models with an aether: wonder how Michelson-Morley works with "flux tubes"?

GregBuchholz2• 11 years ago

You may like the article, "Clearing Up Mysteries - The Original Goal" by E.T. Jaynes:

http://bayes.wustl.edu/etj/articles/cmystery.pdf

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.

...and maybe chapter 10 of his book, "Probability Theory: The Logic of Science".

We are fortunate that the principles of Newtonian mechanics could be developed and verified to great accuracy by studying astronomical phenomena, where friction and turbulence do not complicate what we see. But suppose the Earth were, like Venus, enclosed perpetually in thick clouds. The very existence of an external universe would be unknown for a long time, and to develop the laws of mechanics we would be dependent on the observations we could make locally.
Since tossing of small objects is nearly the first activity of every child, it would be observed very early that they do not always fall with the same side up, and that all one’s efforts to control the outcome are in vain. The natural hypothesis would be that it is the volition of the object tossed, not the volition of the tosser, that determines the outcome; indeed, that is the hypothesis that small children make when questioned about this. Then it would be a major discovery, once coins had been fabricated, that they tend to show both sides about equally often; and the equality appears to get better as the number of tosses increases. The equality of heads and tails would be seen as a fundamental law of physics; symmetric objects have a symmetric volition in falling.
With this beginning, we could develop the mathematical theory of object tossing, discovering the binomial distribution, the absence of time correlations, the limit theorems, the combinatorial frequency laws for tossing of several coins at once, the extension to more complicated symmetric objects like dice, etc. All the experimental confirmations of the theory would consist of more and more tossing experiments, measuring the frequencies in more and more elaborate scenarios. From such experiments, nothing would ever be found that called into question the existence of that volition of the object tossed; they only enable one to confirm that volition and measure it more and more accurately...

http://www.med.mcgill.ca/epidemiology/hanley/bios601/Gaussia...

lmm2• 11 years ago

The wheel of science turns, but it doesn't turn backward. Einstein refined Newton, but in no sense represented a return to Aristotle. Perhaps more to the point, the Bell Inequalities are true and have been experimentally verified; reality provably contains either nondeterminism or nonlocality. If you find the model with instantaneous communication along these "flux tubes" easier to work with then by all means work with it, but it's just another interpretation; most of us find the nondeterministic but local model is ultimately easier to reason about.

yiyus• 11 years ago

"our paper shows that the main empirical argument against classical models of reality is unsound.". That's quite an affirmation!

Strilanc• 11 years ago

Scott Aaronson has commented negatively on a previous paper by the same authors [1]. I don't know if similar issues apply to this one:

[...] the paper advances the prediction that quantum computation will never be possible with more than 3 or 4 qubits. [...] I wonder: before uploading their paper, did the authors check whether their prediction was, y’know, already falsified? How do they reconcile their proposal with (for example) the 8-qubit entanglement observed by Haffner et al. with trapped ions [...]

(Note: that's a critique of the previous paper, not the linked one. Although the linked post mentions quantum computers not working, the linked paper does not touch the subjet.)

1: http://www.scottaaronson.com/blog/?p=1255

btilly5• 11 years ago

They claim to have found a classical system that reproduces quantum mechanical effects. But if they manage to extend it to many particles, interacting, they will find that they have just come up with another interpretation of QM which is experimentally indistinguishable from the rest. And it wouldn't even be the first one. (Bohm's hidden variable theory has precedence.)

Furthermore the "incompressible fluid" they postulate sounds like it enables non-local behavior (which it has to to match current versions of the Bell test) so it is unable to help resolve the issue of reconciling GM with QM.

So this does rather less than they claim. Assuming that their claimed result is correct.

fixermark• 11 years ago

What's the current status of Bohm's hidden variable theory? Does it stand up in light of the Bell test (I was under the impression that the Bell results suggest an arbitrary number of hidden variables would be necessary)?

btilly5• 11 years ago

I don't know and don't keep track. I lost interest after realizing that it can be made compatible with any possible observation.

I'm personally a fan of the Everett interpretation. Also called the many worlds. Which is what you get if you assume that quantum mechanics applies to the observer. Then the act of observation throws the observer into a superposition of possible states where different things were observed. And those states cannot meaningfully interact later for thermodynamic reasons.

Unless someone comes up with good reason to believe that quantum mechanics does not describe humans, I see no reason not to accept it. And if quantum mechanics is replaced by something different, to the extent that quantum mechanics is an accurate description of us, that interpretation remains correct.

sampo3• 11 years ago

What's the current status of Bohm's hidden variable theory? Does it stand up in light of the Bell test

In "normal" quantum mechanics we have the wave-particle dualism. A particle behaves also like a wave, whatever that means.

In Bohm's hidden variable theory, also known as "pilot wave theory" the wave and the particles are separate. The pilot wave is a wave of unknown making (the theory does not say what it would be made of), and this wave follows the normal quantum mechanical behaviour. Then particles "ride" on this wave. So all the quantum mechanical wave effects happen in the pilot wave, and then the classical particle-like particles just follow theirs paths, already laid out by the wave.

Although "spooky action at a distance" is also experimentally verified, explaining this by postulating a wave that fills the whole universe, and explicitly reacts spookily over distances, makes the whole "spooky action at a distance" uncomfortable explicit in this theory, so it doesn't appeal to most physicists.

"The de Broglie–Bohm theory makes the same (empirically correct) predictions for the Bell test experiments as ordinary quantum mechanics. It is able to do this because it is manifestly nonlocal."

http://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory#...

bkcooper• 11 years ago

What's the current status of Bohm's hidden variable theory? Does it stand up in light of the Bell test?

Yes. Bell's theorem doesn't forbid hidden variable theories (in fact, he has a publication preceding his famous result explicitly demonstrating a hidden variable theory that could reproduce QM measurements on a two-level system), just local hidden variable theories. In his collected papers, Bell often remarks that he feels Bohm's interpretation should be more widely studied.

It's a good question why it's not. My understanding, though I'm not well versed in the subject, is that there are some pretty severe shortcomings to it, particularly when you start considering systems with many particles. I've read some of Bohm's writings to try to understand it and as far as I got I found it pretty underwhelming; it seemed more like a bookkeeping trick than any sort of real insight.

ars• 11 years ago

Furthermore the "incompressible fluid" they postulate sounds like it enables non-local behavior

It says compressible not incompressible.

davyjones• 11 years ago

Usually a pretty common mistake. Fluid is always compressible (else sound won't travel in STP water). It is whether one chooses to model the flow as compressible or not.

troymc• 11 years ago

Models like theirs predate Bohm by a long shot. From the introductory paragraph of the paper:

"In 1746 Euler modelled light as waves in a frictionless compressible fluid; a century later in 1846, Faraday modelled it as vibrations in ‘lines of force’ … Fifteen years later Maxwell combined these approaches, proposing that a magnetic line of force is a ‘molecular vortex’…"

They basically updated Maxwell's model. From their conclusion:

"We brought Maxwell’s 1861 model of a magnetic line of force up to date using modern knowledge of polarised waves and of experiments on quantised magnetic flux. Our model obeys the equations for Euler’s fluid and supports light-like solutions which are polarised, absorbed discretely, consistent with the Bell tests, and obey Maxwell’s equations to first order."

What's nice is that their model is classical. Even if it "just" makes exactly the same predictions as other models, it's nice to have a model where physical intuition can be brought to bear.

phkahler5• 11 years ago

> What's nice is that their model is classical. Even if it "just" makes exactly the same predictions as other models, it's nice to have a model where physical intuition can be brought to bear.

A classical model can also be simulated on a classical computer, so if it produces the same results as QM then quantum computation would be... fiction or just redundant?

tjradcliffe6• 11 years ago

The only caveat to this is the ontological status of Faraday's "lines of force". Their model is based on these, and so far as anyone knows they are just a conceptual or pedagogical convenience. They have a quantitative meaning (you can actually calculate the "density of lines of force" between two charges or magnetic dipoles) but they aren't really good for much. They are generally mentioned in passing in intro or intermediate E&M courses, but mostly as a matter of historical interest.

If they could be shown to have independent effect of the kind that the vector potential was shown to have via the Ahronov-Bohm effect, then this whole approach to quantization would become extremely interesting. Otherwise, you're right: it's just another interpretation of QM, and not a very interesting one at that (despite their claims, as I explained in a separate comment, they can't reproduce the experimental violations of the CHSH inequalities in Aspect's and other experiments that introduce time-variation to precisely rule out the kind of prior communication they are arguing for.)

taybin• 11 years ago

"if the fundamental particles are just quasiparticles in a superfluid quantum vacuum"

well obviously.

tjradcliffe6• 11 years ago

This paper has a variety of issues, the most glaring of which is that their "explanation" of the experimental violation of Bell's inequalities (specifically the CHSH form that has been realized in many experiments on polarization) is dependent on a static setup of precisely the kind that Aspect's experiments were intended to avoid.

Aspect's work is one of the most beautiful pieces of careful and precise experimental testing of an idea in the past half-century, and while it has been attacked from many perspectives it is still a very robust argument for the non-locality of reality. One of the important things about it is that the polarization direction was switched in a quasi-random way after the photons had left the source. Variations on this trick have been performed since, and they all agree with the predictions of quantum theory.

The authors say in this paper "The CHSH assumption is not true in Faraday's model. Instead there is prior communication of orientation along phase vortices such as(4), communication which the CHSH calculation excludes by its explicit assumption."

In experiments like Aspects, prior communication is ruled out because the experimental setup is varied in one arm of the apparatus outside forward light cone of the other photon. Each photon gets detected before the other one could possibly know (based on signalling at the speed of light) what polarizer orientation it should be lined up with.

So this is an interesting bit of work that might be useful in creating photonic quasi-particles in magnetic fluids that would allow for study of photon properties that might be difficult to get an experimental handle on otherwise, but the claim that they have a classical model that violates Bell's inequalities in a way that is relevant to the actual experimental work done in this area is considerably overblown.

GregBuchholz2• 11 years ago

I'm not a physicist, but I've always wondered about Caroline Thompson's work, like:

"Chaotic Ball" model, local realism and the Bell test loopholes

http://arxiv.org/abs/quant-ph/0210150

...any thoughts?

tjradcliffe6• 11 years ago

The scrutiny that Bell test experiments get from loophole people is always much appreciated, but the problem with Aspect's results in particular is that lovely parenthetical remark that appears in several of his figures, to the tune of "The dotted line is not a fit to the data, but the quantum mechanical prediction for this result."

While it is easy to imagine selective-detection effects that mess up the results enough to invalidate the test at the level of the inequality, it is very, very difficult to maintain all the physics required for precise, detailed agreement between theory and experiment of the kind that Aspect and others have shown. Here is an example of a "local realistic model" that reproduces the quantum mechanical results for in-time coincidences, but completely messes up any number of auxiliary measurements: http://www.tjradcliffe.com/?p=590

So while I'd love to see a modern version of Aspect's work using state-of-the-art entangled photon sources and the like, the likely reason it hasn't been done is that the odds of it revealing anything new and different are trivially small (but not zero, of course!)

vilhelm_s• 11 years ago

I don't know any physics, but it seems like a bit of a warning sign that these new discoveries in fundamental physics are annouced on... a computer security blog?

nilkn4• 11 years ago

When models like this are proposed, a lot of people are interested because of the philosophical implications of a classical theory of quantum phenomena.

The question I have, though, is this: does this model actually help model phenomena that we can't already model? Quantum gravity is the big spectacular example, but there are many others.

For instance, the Standard Model is very successful at predicting the anomalous magnetic moment of the electron. But it is not successful at predicting the same quantity for the muon. There are many other issues with the Standard Model that aren't so high-flung as quantum gravity.

Are classical models like these, if they can be shown to incorporate multiple particles interacting simultaneously, capable of going beyond the Standard Model or merely replicating it?

snarfy• 11 years ago

Updating this with modern knowledge of quantised magnetic flux

It sounds like they are using quantum mechanics to explain quantum mechanics.

There exists a classical model of the photon after all

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