Quantum behavior in a classical system?

[IttyBittyBit]

So there's a new paper out by Yves Couder's group that observes quantum mechanical-like wave dynamics by averaging the long-term dynamics in a purely classical system. In other words, it's hidden variables.

http://web.mit.edu/newsoffice/2013/when-fluid-dynamics-mimic-quantum-mechanics-0729.html

While the paper focuses purely on the classical aspects of this, the promotional material and accompanying video make a connection to quantum mechanics and promote hidden variables in a not-so-subtle way.

It seems to me that the connection is rubbish and entirely ruled out by Bell's theorem (unless you are willing to posit superdeterminism, which could be a plausible explanation). Anyone have any thoughts?

 

[San K]

So there's a new paper out by Yves Couder's group that observes quantum mechanical-like wave dynamics by averaging the long-term dynamics in a purely classical system. In other words, it's hidden variables.

http://web.mit.edu/newsoffice/2013/when-fluid-dynamics-mimic-quantum-mechanics-0729.html

While the paper focuses purely on the classical aspects of this, the promotional material and accompanying video make a connection to quantum mechanics and promote hidden variables in a not-so-subtle way.

It seems to me that the connection is rubbish and entirely ruled out by Bell's theorem (unless you are willing to posit superdeterminism, which could be a plausible explanation). Anyone have any thoughts?

interesting. Could be the closest represention of wave and its mechanics.. Excitation of a field etc.

It still has to accept non locality. Which they probably do.

their hypothesis/interpretation seems to assume both -

1. Hidden variables
2. Non locality

 

[DevilsAvocado]

Well, if they really managed to replicate the double-slit experiment with a ‘classical droplet’ the result would not have been on MIT News, but on the front page of New York Times.

In 2006, Yves Couder and Emmanuel Fort, physicists at Université Paris Diderot, used this system to reproduce one of the most famous experiments in quantum physics: the so-called “double-slit” experiment, in which particles are fired at a screen through a barrier with two holes in it.

https://www.youtube.com/watch?v=sGCtMKthRh4


This is nonsense. Even a layman like me can understand that you will never get interference from one droplet going thru one slit.

 

[IttyBittyBit]

DevilsAvocado: Not so fast; the 2006 experiment involved two slits, and did indeed observe something akin to double-slit diffraction. I can't shake the feeling, though, that there must be some fundamental aspect of it that is not being reproduced.

San K: That's what bothers me. The dynamics of the 'walkers' appears to be quite local. The walkers ride on their own excitation wave, and the wave is only nonzero around the walker.

 

[IttyBittyBit]

The only non-local property I can think of is the phase of the oscillator, and I'm not sure that really qualifies.

 

[Maui]

It seems they are surprized that the dynamics of a drop of liquid mimic those of quantum waves. I just checked and it's 2013 not 1905 so rediscovering the wave particle duality should probably not shock anyone. Why is this supposed to be surpizing? Sorry if I missed something.

 

[DevilsAvocado]

DevilsAvocado: Not so fast; the 2006 experiment involved two slits, and did indeed observe something akin to double-slit diffraction. I can't shake the feeling, though, that there must be some fundamental aspect of it that is not being reproduced.

Well... the fundamental aspect is that it did not happen as in “used this system to reproduce one of the most famous experiments in quantum physics: the so-called “double-slit” experiment”.

Check out the video @2:12.

 

[DevilsAvocado]

I just checked and it's 2013 not 1905

:thumbs:

 

[IttyBittyBit]

I came here to be skeptical of this research, but it seems I'm the one defending it...

Maui: You mean to say that in 1905 people demonstrated quantum behavior with **droplets** (not waves!) of fluid?

DevilsAvocado: Are you referring to their 2006 work? http://phys.org/news78650511.html (ignore the photo at the top of the page, it just shows a single slit. Experiments with double slits were also done).

The droplet approaches the two slits, then appears to randomly move about (in a very strange way) and 'pick' one of the two slits at random. It then goes throug the slit and, afterwards, is guided by the interference wave. This is basically the same idea as the 'pilot wave' theory of de Broglie. There's nothing special about the wave interference. What's special is that the wave is *generated* by the droplet, and further, the droplet remains stable and propapagates through the slits to the other side. Also, the trajectory of the droplet is chaotic, so even if started from nearly the same initial conditions it will wind up on different points on the screen.

 

[DevilsAvocado]

The droplet approaches the two slits, then appears to randomly move about (in a very strange way) and 'pick' one of the two slits at random. It then goes throug the slit and, afterwards, is guided by the interference wave. This is basically the same idea as the 'pilot wave' theory of de Broglie.

Nope, dBB needs two slits to produce interference:

(and you already know what happens if we measure/block one slit)

There's nothing special about the wave interference. What's special is that the wave is *generated* by the droplet, and further, the droplet remains stable and propapagates through the slits to the other side. Also, the trajectory of the droplet is chaotic, so even if started from nearly the same initial conditions it will wind up on different points on the screen.

And why are not the interference pattern presented? Because there is none!
You can run any single and very chaotic droplet you want, but *one* droplet will never produce this:

 

[IttyBittyBit]

Devils: I'm aware that it needs two slits to work. That's why I referred you to that page. If you read it (and also check out the videos they made), they very clearly show an interference pattern. And yes, the interference pattern is produced by one droplet. They make it quite clear that what is happening is that:

1. The wave generated by the droplet goes through both slits and produces interference.
2. The droplet itself only goes through one slit but is guided by the wave it has generated.

Both of these are in accordance with the double-slit experiment. A single photon will interfere with itself (check) but will never show up in more than one detector (check).

Now I'm not sure what would happen if the separation between the two slits were large. In their experiments it seems to be small. I'm not sure if an interference pattern would be produced if the separation between slits was much larger than the wavelength. That might be something worth investigating.

 

[DevilsAvocado]

Devils: I'm aware that it needs two slits to work. That's why I referred you to that page. If you read it (and also check out the videos they made), they very clearly show an interference pattern. And yes, the interference pattern is produced by one droplet.

I must be missing something here... on this page you have this picture & video:



https://www.youtube.com/watch?v=nmC0ygr08tE

And on this page you have these pictures:

The last page discusses SINGLE-particle interference, which is something else and perfectly expected for one droplet guided by a water wave. We can very easily remove the redundant droplet, and get exactly the same result with plain water:

https://www.youtube.com/watch?v=egRFqSKFmWQ


A great cry and little wool, quoth the Devil when he sheard the hog.

They make it quite clear that what is happening is that:

1. The wave generated by the droplet goes through both slits and produces interference.

Really? Did you watch the video @2:12??

That’s not correct, is it?

 

[IttyBittyBit]

Yeah, that physorg.com article doesn't explain it very clearly I suppose, it was just the only non-technical summary of it I could find. You can check out the original paper (published in Physical Review Letters):

http://people.isy.liu.se/jalar/kurser/QF/assignments/Couder2006.pdf

They do both single-slit and double-slit experiments and clearly show both the graph for single-slit and double-slit interference. FTA:

"The interference fringes are clearly observed and well fitted by this expression. It can be noted that a given droplet is observed to go through one or the other of the slits. However its associated wave passes through both slits and the interference of the resulting waves is responsible for the trajectory of the walker."

 

[Nugatory]

It seems to me that the connection is rubbish and entirely ruled out by Bell's theorem (unless you are willing to posit superdeterminism, which could be a plausible explanation). Anyone have any thoughts?

Bell's theorem rules out local hidden variable theories, not all hidden variable theories. There's no superluminal stuff going on with these corralled waves, so the results could be deterministic yet still match quantum statistics. Indeed, superdeterminism feels like eactly the right interpretation here; this little system has existed and been closed for quite long enough for subluminal causation to determine its entire state.

I'm finding myself thinking that this is a macroscopic analog to the deBroglie-Bohm model plus superdeterminism... Kinda interesting even if there's no compelling new insight - those are few and far between.

(The tone of the MITNews piece sets my teeth on edge, but that's not the fault of the researchers).

 

[bohm2]

As acknowledged by the authors, those experiments are still very far from QM for the following reasons:

- Macroscopic scale : no relation with Planck constant.
- The system is two-dimensional.
- The system is dissipative and sustained by external forcing.
- This forcing imposes a fixed frequency: the “energy” is fixed
- The waves live on a material medium: there is an “ether

Nevertheless, it is interesting that their set-up does generate space and time non-locality via "path memory". See slides:

A macroscopic-scale wave-particle duality
http://www.physics.utoronto.ca/~colloq/Talk2011_Couder/Couder.pdf

 

[IttyBittyBit]

Nugatory: Hrm that sounds about right.

bohm2: Yup, all those 5 points are valid, but the connection is still tantalizing :)

 

[vanhees71]

As far as I understand it, this whole thing has nothing to do with quantum mechanics at all. It's just a classical wave phenomenon which has a mathematical analogy with the wave structure of the quantum mechanical equations of motion for probability amplitudes. This is, of course, interesting but not very surprising.

Mathematical analogies are important in theoretical physics, because one can use methods developed in some field of research in another and it provides a certain form of intuition. E.g., wave equations in fluid dynamics are similar as wave equations in electromagnetism although they describe completely different phenomena, but the mathematical picture provided by the solutions are similar.

 

[bohm2]

Yup, all those 5 points are valid, but the connection is still tantalizing :)

I agree. The most interesting part is the non-locality as summarized in this recent paper by Y. Couder et al. where they discuss the 2 different models proposed by Bohm versus de Broglie's theory of the Double Solution with reference to the diffraction of bouncing droplets:

As a result the wave field is the linear superposition of the successive Faraday waves emitted by past bounces. Its complex interference structure thus contains a memory of the recent trajectory. Furthermore, since the traveling waves move faster than the drop, the wave field also contains information about the obstacles that lie ahead. Hence, two non-local effects exist in the wave-field driving the motion of the droplet: the past bounces influence directly the present (direct propulsion) and the trajectory is perturbed by scattered waves from distant obstacles in a kind of echo-location effect. This interplay between the droplet motion and its associated wave field makes it a macroscopic implementation of a pilot-wave dynamics.

Probabilities and trajectories in a classical wave-particle duality
http://iopscience.iop.org/1742-6596/361/1/012001/pdf/1742-6596_361_1_012001.pdf

As a side note, Gerhard Grossing's et al. group has tried to use some of the insights gained from the bouncing/walking droplets in the experiments of Couder's group to model certain QM phenomena:

In a new approach to explain double-slit interference "from the single particle perspective" via "systemic nonlocality", we answer the question of how a particle going through one slit can "know" about the state of the other slit. We show that this comes about by changed constraints on assumed classical sub-quantum currents, which we have recently employed to derive probability distributions and Bohm-type trajectories in standard double-slit interference on the basis of a modern, 21st century classical physics. Despite claims in the literature that this scenario is to be described by a dynamical nonlocality that could best be understood in the framework of the Heisenberg picture, we show that an explanation can be cast within the framework of the intuitively appealing Schrodinger picture as well. We refer neither to potentials nor to a "quantum force" or some other dynamics, but show that a "systemic nonlocality" may be obtained as a phenomenon that emerges from an assumed sub-quantum kinematics, which is manipulated only by changing its constraints as determined by the changes of the apparatus. Consequences are discussed with respect to the prohibition of superluminal signaling by standard relativity theory...

As we employ no "quantum force", therefore, we consider "systemic nonlocality" as a phenomenon that emerges from a sub-quantum kinematics, which is manipulated only by changing its constraints as determined by the changes of the apparatus. In fact, with our approach we have in a series of papers obtained essential elements of quantum theory. They derive from the assumption that a particle of energy E = ħω is actually an oscillator of angular frequency ω phase-locked with the zero-point oscillations of the surrounding environment, the latter of which containing both regular and fluctuating components and being constrained by the boundary conditions of the experimental setup via the buildup and maintenance of standing waves. The particle in this approach is an off-equilibrium steady-state maintained by the throughput of zero-point energy from its vacuum surroundings. This is in close analogy to the bouncing/walking droplets in the experiments of Couder's group, which in many respects can serve as a classical prototype guiding our intuition.

"Systemic Nonlocality" from Changing Constraints on Sub-Quantum Kinematics
http://lanl.arxiv.org/pdf/1303.2867.pdf

Most of this group's work can be found here:
http://www.nonlinearstudies.at/

I also started a thread on the topic a few years ago with updates:

Wave-particle duality at Macro scale?
https://www.physicsforums.com/showthread.php?t=550729

 

[patfada]

A little while ago I posted a question

The usual interpretation of the double slit experiment, when done with a single photon at a time, is that the photon must interfere with itself. However interference cannot be measured in a single-photon experiment - it requires a large number of photons to manifest a discernible interference pattern.

Suppose that each photon leaves a kind of "wake" in its path which persists over time, and it is the cumulative effect of these "wakes" which results in the observed interference pattern.

Might it be that the path of a given photon is influenced by the paths of the photons which have gone before it?

https://www.physicsforums.com/newreply.php?do=newreply&noquote=1&p=4460761

A number of objections were posted to the idea which I think might be relevant to this discussion:

How do you tell the wake where in spacetime it should be? In which reference frame should it remain stationary? In the lab, moving around the earth, with the Earth moving around the sun and so on all the time? That looks quite arbitrary.

Well, if there is a hypothetical "wake": how is it that the interference appears or disappears only according to whether or not the which slit information is available - and has NOTHING to do with any wake?

you can wait for a longer time interval between each photon...say 1 hour/day/month/year...you would still get an interference patter, after say, an year or more