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Pilot Wave Theory and Its Implications (DeBroglie-Bohm Mechanics, Jerk Drive) by sanman on 21 Oct, 2017 18:22
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Pilot Wave theory is making a comeback, as previous arguments against it are being struck down:
https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-support-20160516/
The dominant orthodox/conventional Copenhagen interpretation of quantum mechanics says that the position of a particle is indeterminate until observation/interaction causes its probability function to collapse into a specific positional value. Meanwhile DeBroglie-Bohmian mechanics says that the position is defined, but it's the trajectory that is indeterminate and guided by a probabilistic wave function.
(Think of Heisenberg's Uncertainty Principle, which says you can't know both position and velocity of a particle at the same time. Copenhagen QM chooses to keep the trajectory well-defined but the position undefined/indeterminate, while DeBroglie-Bohm mechanics chooses to have the position well-defined but the trajectory undefined/indeterminate.)
If the Debroglie-Bohm mechanics can be seen as reliable and correct in its own right, then what are the implications of this? What are the advantages? What kind of devices will it allow us to engineer?
Note that orthodox/conventional(Copenhagen) QM with its perspective of indeterminate states has helped us to accomplish Quantum Computing, whereby the indeterminacy enables a broad spectrum of input states, rather than specific input states.
But so then DeBroglie-Bohm QM would see specific input state(s), proceeding by indeterminate path to some outcome. So just as indeterminacy of states can be expressed/exploited as indeterminacy of inputs (ie. many inputs together), then likewise indeterminacy of paths could be expressed/exploited as many paths together.
This could be useful when we want to start out from a specific starting point, and travel many routes at once, to discover which route is the least difficult.
By seeing quantum indeterminacy as all types of motion at once, instead of as all types of positions at once, we can construe motion as a transform, and then use Quantum Computing as a means to solve all possible transforms of a particular input state.
But leaving computing aside - does the idea of all possible velocities allow FTL velocities?
Conventional/orthodox QM implies it by saying a particle can tunnel from any position to any other position instantaneously - and it's from that we infer that the quantum particle is able to defy the speed limit of C. But DeBroglie-Bohmian mechanics would say this more explicitly - ie. "all possible velocities means all possible velocities" (for a tiny quantum particle).
If quantum experiments based on conventional/orthodox QM have demonstrated instantaneous displacement / Quantum Teleportation of particles (even large numbers of them) from one position to another, then what might experiments based on DeBroglie-Bohm mechanics show? Perhaps Quantum Acceleration - an instantaneous change in velocity (for tiny quantum particles) requiring no work whatsoever.
What if you were to do that for a large number of particles? Analogous to the idea of conventional QM teleporting a bunch of particles from one positional location to another arbitrarily distant one, what if you could likewise instantly accelerate a large number of particles to some arbitrarily high velocity? Could that be possible?
It was in the 1940s-50s that science fiction writers first came up with the idea of the "Jump Drive" for FTL travel. Isaac Asimov had them in his Foundation books, and Robert Heinlein had them in Starman Jones (still one of my favorite Heinlein novels). The "Jump Drive" allowed a spaceship to move from one part of space to another nearly instantaneously, like Quantum Teleportation allows for tiny quantum particles.
What would be the DeBroglie-Bohmian equivalent of this? Could it be called a "Jerk Drive"?
If the analogy holds true, you'd be able to instantaneously accelerate a particle (or group of particles) from one velocity frame to another. (Okay, for sci-fi purposes, we'd aspire to do this to an entire spaceship, not just a particle. When I think of those special fx on Star Trek, where the ship seems to elongate and flash out of sight, that's also how I'd imagine that space travel by Jerk Drive would look.) -
#1 by meberbs on 21 Oct, 2017 21:09
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Pilot Wave theory is making a comeback, as previous arguments against it are being struck down:
The article is claiming experimental support for pilot wave theory, but this doesn't make any sense. The important point is that they are saying that the experiment results match pilot wave theory, but they do not mention what the Copenhagen interpretation says. For their experiment it sounds like the results are also consistent with the Copenhagen interpretation. With both theories predicting the same result, the results of the experiment are irrelevant. The only important thing would be that they have come up with a way to show theoretically that pilot wave theory is consistent with Copenhagen in this case.
https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-support-20160516/
Until someone comes up with the equivalent of Bell's inequality for these 2 interpretations of quantum, no experiment can be claimed to differentiate between them.
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#2 by sanman on 21 Oct, 2017 22:22
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The article is claiming experimental support for pilot wave theory, but this doesn't make any sense. The important point is that they are saying that the experiment results match pilot wave theory, but they do not mention what the Copenhagen interpretation says. For their experiment it sounds like the results are also consistent with the Copenhagen interpretation. With both theories predicting the same result, the results of the experiment are irrelevant. The only important thing would be that they have come up with a way to show theoretically that pilot wave theory is consistent with Copenhagen in this case.
Until someone comes up with the equivalent of Bell's inequality for these 2 interpretations of quantum, no experiment can be claimed to differentiate between them.
That's an interesting point - I wonder what a Bell's Inequality under DeBroglie-Bohm would look like?
Would Bob and Alice be zipping by each other in different velocity frames? Because the situation sort of seems like "Spooky Action After a Collision"
Bob & Alice ...
in Copenhagen: "We were located together, we're now apart, but are still connected"
in DeBroglie-Bohm: "We were traveling together, we've now taken different paths, but are still connected"
https://en.wikipedia.org/wiki/Bell_test_experiments
To more robustly carry out Bell Inequality experiments involving different velocity frames, we might want to make use of spacecraft with their high Delta-V.
Hopefully the falling costs of space travel could make that more feasible.
But until then, at least Bob and Alice will always have Copenhagen.
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#3 by sanman on 22 Oct, 2017 01:25
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Here's a nice explanation on DeBroglie-Bohm by way of Hidden Variables Theory:
https://en.wikipedia.org/wiki/Hidden_variable_theory -
#4 by sanman on 24 Oct, 2017 01:08
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Check this out:
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#5 by sanman on 24 Oct, 2017 23:51
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Until someone comes up with the equivalent of Bell's inequality for these 2 interpretations of quantum, no experiment can be claimed to differentiate between them.
Beyond just Bell's Inequality and the search for Hidden Variables, also consider that DeBroglie-Bohm/Pilot Wave Theory may also make some unique predictions which could be tested for.
Please read the following:
http://discovermagazine.com/2017/may-2017/the-war-over-realityQuoteValentini has devoted his career to almost single-handedly resurrecting the pilot wave idea. Now his years of work actually have a chance — a small one, he admits — of being vindicated. Of the many interpretations of quantum theory, pilot wave theory is unique in that Valentini has found a way in which it might be experimentally tested. No other interpretation of quantum mechanics can make that claim. Many Worlds, Bohr’s interpretation and others are all experimentally indistinguishable — they reproduce the results of standard quantum theory. But if Valentini is right, certain effects predicted in pilot wave theory may have left an imprint on the cosmic microwave background, the primordial radiation left over from the Big Bang that still pervades all of space.
The temperature of that radiation is almost a perfectly uniform 2.725 degrees Celsius above absolute zero. Detailed observations, however, have found slight variations in the radiation. Standard quantum theory can explain nearly all of these variations, but in 2015, new data released by the European Space Agency’s Planck spacecraft revealed evidence of small anomalies in the background radiation. And that is just the kind of thing Valentini has been looking for. While conventional quantum theory predicts that random quantum fluctuations in the early universe have left celestial imprints, pilot wave theory predicts fluctuations that are less random, leaving slightly different wrinkles in the cosmic microwave background radiation.
“It’s tantalizing,” Valentini says. “We’re carrying out the analysis partly to understand things better and partly to see what the data can tell us about the predictions that we have.” Another two years of data and analysis should settle the question.
So at some point, physical/experimental evidence may be found which vindicates DeBroglie-Bohm / Pilot Wave Theory over the Copenhagen interpretation.
Note that DeBroglie-Bohm /Pilot Wave Theory does allow for Faster-Than-Light Communication, which is how the Pilot Wave would be instantly modified across the entire universe by the Non-Local influences (variables).
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#6 by timothy9000 on 20 Dec, 2017 16:04
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Here are two experiments worth noting:
Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer
http://science.sciencemag.org/content/332/6034/1170.full
Experimental nonlocal and surreal Bohmian trajectories
http://advances.sciencemag.org/content/2/2/e1501466.full
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#7 by robus on 10 Jan, 2018 21:03
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I’m no physicist, but the elegance of Bohmian Mechanics is very appealing. Surely the proof would be in deriving a unified theory, something the standard model has been twisting itself into knots (made of string?
) to accomplish.
Good luck to researchers looking at a new (and old) approach. -
#8 by ppnl on 11 Jan, 2018 04:19
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Yeah, I remember when this came out several years ago. I wasn't impressed.
First some clarity. Quantum mechanics is not non-local. Yes there is a strange looking correlation but no thing or information has traveled faster than light. What you are seeing is a projection and it no more allows faster than light communication than a shadow traveling faster than light allows FTL communication. There is no object traveling and so no information transfer.
Bohmian mechanics absolutely is non-local. That means it can signal backwards in time and to violate Bell's inequality it absolutely must signal backwards in time. Now you can either bite the bullet and allow time travel or you can introduce a mechanism that makes the pilot wave forever out of reach of measurement. But then BM collapses to making all the same measurable predictions as normal QM. The pilot wave becomes an unneeded extra tacked on for purely philosophical reasons.
And finally how does the pilot wave deal with other quantum numbers like for example spin? Locally the spin has a definite value but when you try to measure it the pilot wave sends a signal to some distant particle that changes the spin of both particles? Why? How does it keep up with who to send signals to? And if it makes no new and different predictions then what good is it?
If you are in to this kind of thing you should just look into super-determinism.
) to accomplish.