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.)
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.
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.
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.)
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)?
"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?
> 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.
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.
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.
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.
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).
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.
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.
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".
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.
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"?
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?
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?
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.
Strilanc|11 years ago
> [...] 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
btilly|11 years ago
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.
troymc|11 years ago
"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.
tjradcliffe|11 years ago
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.)
ars|11 years ago
It says compressible not incompressible.
fixermark|11 years ago
cevn|11 years ago
How long would I have to study physics to be able to understand everything in this sentence?
sampo|11 years ago
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.
fdej|11 years ago
clavalle|11 years ago
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
jerf|11 years ago
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.
Iftheshoefits|11 years ago
angdis|11 years ago
dkarapetyan|11 years ago
yiyus|11 years ago
phkahler|11 years ago
lisper|11 years ago
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.
sp332|11 years ago
maaku|11 years ago
pbhjpbhj|11 years ago
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"?
nilkn|11 years ago
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?
vilhelm_s|11 years ago
snarfy|11 years ago
It sounds like they are using quantum mechanics to explain quantum mechanics.
taybin|11 years ago
well obviously.
tjradcliffe|11 years ago
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.
GregBuchholz|11 years ago
"Chaotic Ball" model, local realism and the Bell test loopholes
http://arxiv.org/abs/quant-ph/0210150
...any thoughts?