Friday, April 1, 2016

Yves Couder's bouncing droplets
Was Einstein wrong again?

One quantum mechanics interpretation is de Broglie-Bohm pilot wave theory where a particle is guided by the so-called quantum potential. While the mathematics of it are well known, the question is if we can actually simulate it in the laboratory. Enter the world of Yves Couder's bouncing droplets. 

The setting is that of an oil bath to which vibration is applied from below. The amplitude is low enough to prevent creating waves. When a droplet is dropped on the surface it will bounce and create a wave. Then the wave and droplet interact creating a wave-particle "duality". See the Morgan Freemen's video below from the Science Chanel: "Through the Wormhole".

The question is if this experiment can be understood as a genuine explanation of quantum mechanics. Yves Couder does not make such a claim but at minute 3:36 Morgan Freeman claims somebody does and I am not sure what the argument really is. Perhaps Bill Nye the science guy could provide some quantum mechanics clarifications. 

Here is another video that enlightens us a bit more:

But what would bounce in the case of quantum mechanics? Nothing at all, in other words the aether. The aether was disposed as a concept by Einstein in his special theory of relativity, but Bohmian mechanics does allow speeds higher than the speed of light, so could Einstein have been wrong?

Einstein was wrong on several occasions: it is generally accepted that he lost his debate with Bohr, his first prediction of the bending of light rays by the Sun during an eclipse was off by a factor of two, and he attempted to publish a paper in which he predicted that gravitational waves do not exist. So was he correct in his special theory of relativity? And what would power the vibrations in the case of quantum mechanics? Uri Geller seems to suggest that the Big Bang echo that still reverberates today as the cosmic microwave background radiation could provide the vibration similar with what Couder does to the oil bath. But what about the special theory of relativity itself? What is the correct theory? The director of the Einstein Centre for Local-Realistic PhysicsJoy Christian, has generalized the theory of inertial structures and provided the correct replacement of the special theory of relativity which can be put to the test  by observations of oscillating flavor ratios of ultrahigh energy cosmic neutrinos, or of altering pulse rates of extreme energy binary pulsars. This genuine breakthrough in correcting special theory of relativity was followed by more amazing breakthroughs in understanding quantum mechanics and uncovering the deep geometric structure of a complete description of reality as a parallelized 7-sphere. Moreover, in a related work of the same quality and caliber, it looks like torsion energy is mostly responsible for the mass of fermions as Fred Diether III, the operating director of the center, has shown. Should the Nobel committee withdraw Peter Higgs' prize and awarded it instead to Fred Diether and Joy Christian? You bet. At the very minimum, what mathematicians call Hodge duality should be renamed Christian duality in honor of the correct generalization of it which put to shame the quantum foundation community. Unfortunately this community follow blindly the dogma of "the most pointless" discovery, Bell's theorem. Just like von Neumann theorem was discredited, so too Bell's theorem is a modern scandal as well.



  1. I know that this post is intended to be a joke, but today is 2nd of April so I'll point you to an interesting article by Robert Brady and Ross Anderson:

    "Why bouncing droplets are a pretty good model of quantum mechanics"

    This is their conclusion:

    "We have derived from first principles that bouncing droplets are, to a rather good approximation, Lorentz covariant, with
    c being the speed of surface waves; that they obey an analogue of Schrodinger's equation where Planck's
    constant is replaced by an appropriate constant
    of the motion; that the force between them obeys
    Maxwell's equations, with an inverse-square attraction and an analogue of the magnetic force;
    and finally that orbiting droplet pairs exhibit
    spin-half symmetry and align antisymmetrically
    as in the Pauli exclusion principle.

    If their math is correct, it is a pretty amazing result.


    1. Hi Andrei,

      I hope the post was funny and it was clear when the nonsense began: I used the Uri Geller reference (the charlatan who claimed he can bend spoons with his mind) to mark the transition. On the droplets, Yves Couder does not make any wrong claims and he strategically steers clear of quantum mechanics. Regarding QM, his stuff falls into the realm of toy models, but by their very nature you need to take them with a pinch of salt.

  2. I remember this a while back. It is a sort of analogue simulation of quantum mechanics in the Bohm interpretation. It is an interesting demonstration, but it does not necessarily give empirical weight for Bohm's QM.

    There is nothing particularly wrong with Bohm's quantum interpretation or formalism. The complex wave function in polar form permits us to split the Schrodinger equation into a real and imaginary parts. The real part is the Hamilton-Jacobi equation modified with a quantum potential. The imaginary part is a continuity equation for a fluid, called the pilot wave. David Bohm thought he had a hidden variable with local properties, and he was wrong on that.

    If you perform a symplectic transformation of this classical-like system you get a different active channel. The active channel is what Bohm called the path the particle or beable followed. The canonical transformation adjusts the quantum potential in such a way that you get a different path. Due to the classical-like nature of this formalism the transformation principles are unitary-simplectic, or Usp(n). If you sum over all symplectic transformed paths you get a form of path integral.

    Bohm's formalism might be of use for problems with quantum chaos. Since there is no explicit Hilbert space there are no methods for finding the production of particles. As a result it is not able to work with relativistic interacting fields, such as QED. Its limited utility has prevented it from being widely accepted, and its inception as a claimed local hidden variable theory has brought it some infamy.


    1. Hi Lawrence,

      I know papers which claim Bohmian works in quantum field theory and I am carefully studying them. So far I am not convinced by them and I am looking to rigorously prove the incompatibility of Bohmian with QFT.


    2. There is the mathematician at Rutgers, Sheldon Goldstein, who has been promoting this. It is interesting that he and others labor intensely to solve problems solved ordinarily over 60 years ago.

      There is maybe one lesson in it. Bohmian QM is really just plain quantum mechanics. It is a way of representing the Schrodinger equation. You can do the same with the Klein-Gordon equation. Yet because there is no Hilbert space or discrete ladder of states you can't work with quantum field theory. We might ponder whether a similar lack of machinery might be hindering quantum gravity.


  3. Lawrence Crowell:

    "It is a sort of analogue simulation of quantum mechanics in the Bohm interpretation. It is an interesting demonstration, but it does not necessarily give empirical weight for Bohm's QM"

    I think these experiments eliminate the need for Bohm's interpretation, because they show that it is possible to get quantum effects without the need of non-locality or non-realism. They provide strong evidence that classical field theory has the potential to explain the world in a local and Lorentz invariant way. The rejection of classical local realism has become, in my opinion, logically unjustifiable.


    1. I don't think this eliminates Bohm's QM. The one problem is that the wave here is real valued, while in QM the so called pilot wave is imaginary, or at least the continuity equation is the imaginary part of the SE.

      There are a lot of interpretations of QM, and in effect different features, local causality, wave function reality, unique determined path, etc are toggled on or off. Some have a great utility and others not so much. Bohm's QM is in the "not so much" category.


    2. "Eliminate" is a strong word. However, the appeal of Bohm's theory is that it is well-defined, clear, it doesn't rely on fuzzy concepts like "observer", etc. It seems to present an objective picture of the world. But it also have some not-so-good features like non-locality, and a real, objective wave function which does not reside in the normal 3d space, etc. The proponents of the theory claim that these features are a necessary, inescapable implication of quantum physics so they shouldn't be seen as arguments against it.

      Yves Couder's experiments prove them wrong. You can get quantum behaviour without non-locality, without complex numbers, multi-dimensional wave-functions. All you need is a classical, deterministic field and some imagination.

      Sure, it remains to be seen if the analogy coud be elevated to a proof, but the evidence points in that direction.


    3. Andrei,

      It is simple to see that, despite the similarities, Yves Couder's experiment has nothing to do with QM: Bell's theorem. Bohmian QM is contextual and avoids Bell's theorem in this way, while Yves Couder's experiment is non-contextual and satisfies Bell's theorem. This is the simple reason Yves Couder himself does not make the claim his experiment is a classical realization of QM.

      Any suggestion by QM experts that bouncing droplets are quantum in nature is disingenuous. While there is some hype, I know no published paper which makes such a claim. Show me one and I will write a rebuttal to it.


    4. Florin,

      Bell's theorem is pretty much irrelevant when dealing with deterministic theories. Classical field theories, like Maxwell's electrodynamics or general relativity do not allow for the existence of independent subsystems, so the detector settings will always be correlated. Even naive models like a clockwork universe cannot be ruled out by Bell's theorem for the same reason.

      In the oil drop experiments the drops do not move independently of one another so, again, such a model could produce violations of Bell's inequality.

      The model is contextual because the waves guiding the drops depend on the geometry of the bath and the presence of other drops.

      The experiment cannot be presented as a classical realization of QM because it is not about electrons and quarks but about oil drops. It is however a proof that quantum effects are obtainable in a pure classical setup.

      The paper I linked in my first reply claims that an analog of Schrodinger's equation (except for the value of Plank's constant)describes the motion of the drops. This implies that all quantum effects, including entangled states can be reproduced. Feel free to rebut the paper.


  4. Haha! This was really funny! I just found it today. When you mentioned Uri Geller I thought was a random joke, but then I saw immediately below you mentioned another guy, and I was certain you wrote it on April 1st.

    I don't understand this fuzz about simulating a Bohmian particle with droplets. I mean, it was clear for long time that for the position only of a single particle things can work (modulo Bell-Kochen-Specker's result). I'd love to see these guys trying do the same for two entangled particles.

    Some years ago, as someone who would prefer things to have reality in physics, I gave a lot of patience and consideration to the pilot-wave theory. I even bought 4 books by David Bohm, and read them, but I was very unconvinced - a too complicated mechanism with more problems than it aims to solve. I think the modern formulation, as it can be found in this book, is much better.

    However, even the modern formulation of the pilot-wave theory, claimed by its supporters to solve the most important problems of quantum mechanics, has in my opinion a big problem. Letting aside the necessity to conceal the mechanism from being observed by any experiment, and the tension with special relativity, I think the biggest problem is that this theory does nothing. If you start with point-particles and let them to be guided by some potential, given by the pilot-wave, and try to make it reproduce the observations, you necessarily end up with endowing the pilot-wave itself with all the properties you initially hoped the point-particle has. Take for instance the Hydrogen atom in its ground state. The point electron, according to Bohmian mechanics, has to have a fixed position. But this would make the atom a sort of dipole which is not, so you will have to admit that the charge density is an attribute of the pilot wave, which is spread around the nucleus. Also, consider the Mach-Zehnder interferometer ( In the interferometer, if you remove the second beam-splitter, according to the theory, a Bohmian particle would have to turn 90 degrees in the place where the beam splitter was removed, so where is nothing to interact with (except the potential), and reach precisely the opposite detector than that a classical particle would reach. So if we would record the kick in the deflecting mirrors, we would see that we can't attribute momentum to the Bohmian particle, only to the wave itself. So charge and momentum are attributes of the wave, not of the particle. Eventually, you realize that all physical observables, including spin, are attributes of the pilot-wave, and not of the point particle. The only role of the Bohmian particle remains to be plugged into the formula when is detected, but this is akin to the wavefunction collapse. So Bohmian mechanics is about a wavefunction that evolves according to the Schrodinger equation, and collapses at measurements, just like in standard quantum mechanics. The Bohmian particle does nothing at all, just marks the positions where the detection took place, but this does the pilot-wave too, when it collapses. So I think the Bohmian particle can be removed without any loss, and what you get is standard quantum mechanics. Last year I started working on a paper describing this with more technical details, but I put it on hold because I have other things to do.

    1. Thanks, I put 4/1/2016 at the end of the text :)

      What you said about Bohmian is very interesting, I did not consider that kind of point of view before. Do you want to have a guest post on this? Maybe I can get someone to reply to it.

    2. This comment has been removed by the author.

    3. Sure Florin, thank you for the invitation. I have to prepare it, but first I have some work to do, which will take me some time. Then I will present the arguments as clear as I can, and we will try together to engage some active researchers in Bohmian mechanics to reply. Bell was one of the greatest expert in the foundations of quantum mechanics, the one who found the theorems about non-locality and contextuality, the two major enemies of the early hidden-variable theories. Yet, 20 years later, he was still very confident that the pilot-wave theory was the right way. People actively researching in Bohmian mechanics took care to resolve most of the problems of the theory, and I don't expect to disarm them with my previous comment alone, so I have to prepare properly first, and this takes some time.