Monday, June 30, 2014

"Proof" of Pilot Waves from Fluid Dynamics?

This Wired article seems to indicate that the evidence for the validation of Bohmian's "Pilot Wave" idea for quantum mechanics can be found in some fluid dynamics experiment.

In a groundbreaking experiment, the Paris researchers used the droplet setup to demonstrate single- and double-slit interference. They discovered that when a droplet bounces toward a pair of openings in a damlike barrier, it passes through only one slit or the other, while the pilot wave passes through both. Repeated trials show that the overlapping wavefronts of the pilot wave steer the droplets to certain places and never to locations in between — an apparent replication of the interference pattern in the quantum double-slit experiment that Feynman described as “impossible … to explain in any classical way.” And just as measuring the trajectories of particles seems to “collapse” their simultaneous realities, disturbing the pilot wave in the bouncing-droplet experiment destroys the interference pattern.

Droplets can also seem to “tunnel” through barriers, orbit each other in stable “bound states,” and exhibit properties analogous to quantum spin and electromagnetic attraction. When confined to circular areas called corrals, they form concentric rings analogous to the standing waves generated by electrons in quantum corrals. They even annihilate with subsurface bubbles, an effect reminiscent of the mutual destruction of matter and antimatter particles.

OK, let's be VERY clear on this, shall we? In this experiment, there is a very important feature here that needs to be  pointed out. We can DETECT these "pilot waves" that are steering these droplets. This is a very, VERY, important point here. In QM, these pilot waves have NEVER, EVER, been detected. That is a very significant difference, and the main factor why the pilot-wave model hasn't caught on! Trust me, if there's physical evidence for it, physicists WILL adapt it! As of now, there are no deviations between the predictions of the conventional QM versus the pilot-wave picture. So how can one tell which one to accept beyond just a matter of taste and personal preferences?!

The other thing that needs to be pointed out is that this is, at best, an ANALOGOUS situation to the pilot-wave picture. It is NOT an identical situation. The "discovery" of magnetic monopole in the spin-ice system did not turn elementary particle and EM upside down, because while these "monopoles" sure have the same characteristics of the bare monopoles, they are, at best, only analogous to them. These are still NOT what we are looking for! It is not the same thing.

Until there is direct evidence of such pilot wave, or until there is evidence that support the prediction of pilot-wave but not the regular, conventional QM picture, then we have no strong evidence to support or falsify one or the other. Period. It is irrelevant how many droplets and wave experiments one performs.



Steve W said...

Does the pilot wave interpretation actually differ from the standard QM formulation in terms of physical predictions? I was under the impression that they were mathematically equivalent.

This reminds me of an interview I read a couple years ago where the lead investigator touted some experimental results as being "entirely consistent with the pilot wave theory" and this was meant to be a big deal. BUT, upon further inspection, both interpretations led to the same predictions about the experiment, so the statement was basically meaningless. The same article claimed that weak measurements were somehow violating the uncertainty principle. Bleh!

Unknown said...

I don't think the lack of direct detection of pilot waves is a fair criticism. Gravitational waves have never been directly detected and yet most mainstream physicists accept their existence. Pilot waves may have not been detected yet but there hasn't exactly been an effort to try to find them either.

ZapperZ said...

I disagree. The existence of gravitational waves are NOT accepted by all mainstream physicists, and certainly, there are no established consensus yet for its existence. Otherwise, what's the point in LIGO, LISA, etc.?

Pilot waves have not been detected not because no one is trying to find them, but because there are no mechanism of such detection. Note that there have been experiments employing "weak measurement" detection that have averaged out to be consistent to such pilot wave picture. Do a search of this blog to find one such example. So the claim that no one is looking for it is false.