11 ms·

Why don't more physicists subscribe to pilot wave theory?

119 points by rfreytag 10y ago

JshWright 10y ago
If you're interested in this sort of thing as a lay person (as I am), I would recommend the PBS Space Time YouTube channel. Be sure to stick around for the end of each video, as he often calls out comments on earlier videos that contain corrections or clarifications (in many cases, from _very_ highly qualified physicists and other subject matter experts). Here's their recent episode on pilot wave theory: https://www.youtube.com/watch?v=RlXdsyctD50 https://www.youtube.com/watch?v=RlXdsyctD50
- mblaney 10y ago
  Thanks for the video. He mentioned that the pilot wave is made up of "some stuff", but never got back to that being one of the unknowns of pilot wave theory. Seems like that questioned will need to be answered before it is taken more seriously.
  - combatentropy 10y ago
    > He mentioned that the pilot wave is made up of "some stuff" Could the stuff be dark matter or dark energy?
    - naasking 10y ago
      Pilot waves aren't made of anything, they are a description of configuration space. Think of it like this: to describe particle motion, take the ordinary/classical equations of motion, and now add another term to account for quantum behaviour. The force exerted by this term at time t is a function of the position of every other particle in the universe at time t, no matter the distance. That's pilot wave theory, where this term is sometimes called the "quantum potential" and is governed by Schroedinger's equation. As you can see, this extra term goes to zero when quantum effects become negligible and we recover classical mechanics straight away. The difficulty is the obvious nonlocality and what that means for special relativity.
      - bmh100 10y ago
        Could this connection to the rest of the universe be considered conceptually similar to a form of entanglement?
        naasking 10y ago
        Sort of. There is no real entanglement in this formalism, not in the way it's typically portrayed. I suppose you could say entanglement is there all the time. Macroscopic observation of entanglement via non-local correlations is really just a context in which we make the non-local connection observable.
lisper 10y ago
This is the bottom line: "It's been demonstrated experimentally that you can't have a local, deterministic, real, definite theory (i.e. that would lead to demonstrably false conclusions). People intuitively expect all of those things to be true, but we can prove that it isn't the case. The various interpretations all try to give up one of "local", real", "definite", or "deterministic" in order to preserve the others, thus preserving at least a modicum of their intuition. The pilot wave idea gives up on locality" And I will add: Multiple worlds gives up on definiteness. "Zero worlds" (my personal favorite) gives up on realism. And, of course Copenhagen gives up on determinism. Take your pick. Or go with decoherence, which kind of lets you turn a knob to give up a little bit of all four and dial in whatever setting you like.
- phkahler 10y ago
  But if someone makes a conscious choice to choose one that preserves locality, shouldn't they change their mind when "spooky action at a distance" starts happening? Non-locality is staring them in the face and they refuse to adopt a formalism that makes it explicit. They seem to like things that appear strange and non-intuitive.
  - combatentropy 10y ago
    I agree. I thought that the scientific world already gave up on the idea of locality, since entanglement has been experimentally demonstrated. Furthermore, I don't have a problem with accepting non-locality from a theoretical perspective either, now that I know about the Holographic Principle. If the universe is a hologram, then the apparatus that is projecting the hologram can be connected in ways that aren't obvious in the hologram.
    - otakucode 10y ago
      It's not that kind of a hologram... all the hologram idea says is that all of the information in our universe can be represented on a 2 dimensional surface. It doesn't claim there is literally a hologram projector somewhere projecting a hologram of our universe. Such a thing would be nonsensical. If the projector were outside our universe it would, by definition, be causally disconnected from our universe and thereby never capable of influencing it in any way. If it were capable, it would, again by definition, be part of our holographic universe.
contravariant 10y ago
I would have though the fact that the pilot wave theory uses the (multi-particle) Schroedinger equation, while most modern physics is based on field theory, would be more important. So far I've seen no formulation of the pilot wave theory in a way that incorporates fields, or provides some other mechanism to account for things like the annihilation of particles.
- dnautics 10y ago
  If I'm not mistaken, It's just formalism. Mathematically a continuous wave function is equivalent to a countably infinite vector space. It can be hard to switch between the two (as a chemist we are taught Schroeder and I have a hard time wrapping my head around Heisenberg)
  - chestervonwinch 10y ago
    > a continuous wave function is equivalent to a countably infinite vector space I think you mean that the function is a point in the vector space. More precisely, it is a point in a particular separable Hilbert space, i.e., a complete vector space equipped with an inner product that has countable, dense basis.
    - dnautics 10y ago
      right, sorry. The space of continuous wave functions are equivalent to a countably infinite vector space.
- naasking 10y ago
  There are plenty of field theory extensions for Bohmian mechanics. Due the relatively few people working on it, no single approach has become dominant.
- jostylr 10y ago
  There are various versions, but the one I recommend to date loses determinism (that was never the point) and allows for annihilation and creation of particles: https://arxiv.org/abs/quant-ph/0208072 https://arxiv.org/abs/quant-ph/0208072 In addition, the ideas of Bohmian mechanics has led to a new direction in dealing with the divergences in QFT, that is, in finding a version of it that is mathematically well-defined: https://arxiv.org/abs/1506.00497 https://arxiv.org/abs/1506.00497
tzs 10y ago
Would this be kind of the physics equivalent of nonstandard analysis in mathematics? Nonstandard analysis (NSA) is an approach to analysis that essentially makes rigorous the vague notions of infinitesimals that Newton and Leibniz and the other pioneers of calculus based their work on. Newton's fluxions and Leibniz's differentials provided great guidance, and in a lot of cases they even worked and gave correct results, but they were not really rigorously defined, and later mathematicians started running into serious problems with that approach. Those were resolved with the approach that we all now known and love (loath?): limits and the epsilon/delta approach to them. NSA extends the real field to contain a new kind of number that is positive but is less than 1/N for any integer N, giving a new field called the hyperreals. You can then do things like define the derivative of f at x to be (f(x+h)-f(x))/h where h is an infinitesimal, work out that using ordinary algebraic manipulations, and then just drop any terms that are infinitesimal. NSA goes far beyond just calculus. You can use these ideas all through analysis. Seems pretty cool, and a lot clearer than a limits approach. So why has it not taken over? I believe that a big part of it is that it has been shown that NSA and standard analysis are equivalent. Anything that you can prove in one can be proven in the other. Perhaps more important, one doesn't seem any better than the other at leading to deep insights. If you can't solve a problem in standard analysis, you probably aren't going to figure out the solution if you use NSA, and vice versa. So while it might be overall nicer if we were starting from scratch to use NSA instead of standard analysis everywhere, so much is already done in standard analysis that switching now would be too painful.
- millstone 10y ago
  Interesting analogy but I'm not sure if it holds. Infinitesimals are an alternative to the limit-based formalism typically seen. It changes the way you do calculus. However Bohmian Mechanics is a different interpretation, not a different formalism. You can accept the interpretation, but you still end up solving the Schrödinger equation in the same way, using the same mathematical methods. The analogy works better for matrix mechanics as compared to Schrödinger's wave mechanics. These are mathematically quite different even though they give the same results.
  - jayajay 10y ago
phkahler 10y ago
Since the pilot wave theory is deterministic, wouldn't someone be able to simulate a quantum computer with a classical one in reasonable time and storage?
- otakucode 10y ago
  What would make you think that? Deterministic doesn't imply predictable, reducible, or low complexity. Even a purely deterministic simple system can be capable of (and most are) chaotic behavior whose information content would grow faster than any system smaller than itself could predict. In other words, the only way to "simulate" the system would be to completely reproduce every bit of it, and let it evolve in realtime. And practically speaking, we can't even approach that.
  - jayajay 10y ago
    For example, the double pendulum: https://en.wikipedia.org/wiki/Double_pendulum https://en.wikipedia.org/wiki/Double_pendulum. That said, the phase space of a double pendulum is bounded.
    - duckingtest 10y ago
      It's really funny that something as simple is impossible to predict over longer times, because you would need perfect information. Yet climate science is 'settled'.
      - jayajay 10y ago
        Take an undamped double pendulum and divide the space up into 2 sections. Suppose you can only check which section the pendulum is every N seconds. Every time you check, you record the value, and over time you build up a sequence of K numbers: 1,0,1,0,0,1,1,1,1,0,0,1,0,... Suppose you know the exact initial state (dx/dt, x) of the pendulum. What bounds on K and T are required such that the sequence of numbers is asymptotically indistinguishable from a purely random sequence? So, because of a silly thought experiment, one might think there is very simple order to the apparent randomness. But, as Pauli would say, "it's not even wrong"...
ClayFerguson 10y ago
There is one other interpretation of Pilot Wave theory that is sort of the "inverse" of Pilot Wave. and to me makes more sense. The PW may be correct but the particles are not following a wave that is moving around them. What is happening is that each particle is 'emitting' (spherically and radially outward from itself) a wave of its own. It is the interaction of all other waves that cause the particle to move. Just like a particle with mass distorts the spacetime around it, in a 'static way', perhaps charged particles distort spacetime in a way that is directly tied to the speed of light, and thus distort spacetime in a 'dynamic way'. But the fact that the slit experiment "works" even when we know only a single particle at a time is being sent thru, it just makes more intuitive sense that the particle is neither interacting with itself, nor with other universes (copies of itself). So what i'm saying is PW theory is FAR more intuitive than Copenhagen many-worlds to me. I believe there is genuinely one particle going thru the slit experiment when we think there is, and it follows the path thru in a way that is statistically determines much more by a PW-type theory than any other theory.
scythe 10y ago
I have a fond memory of taking an advanced (graduate) seminar class with taught by one of the oldest professors at my university -- and attended by another. The lecturer was describing something to do with manifolds and various obscure formulations of classical field theories and he mentions that he was at a lecture once where someone had related this theory to Bohmian mechanics -- the other professor cut him off "It's wrong" A student held up his hand and asked what Bohmian mechanics was. Before the lecturer could answer "Don't worry, it's wrong" It was difficult to contain myself.
- dmichulke 10y ago
  Related: http://www.phdcomics.com/comics.php?f=1912 http://www.phdcomics.com/comics.php?f=1912
bicubic 10y ago
There's one major shortcoming that the answer doesn't seem to touch on: pilot wave theory doesn't explain relativity whatsoever, while quantum field theory does. We've experimentally confirmed relativity, so at best, pilot wave theory is incomplete.
- naasking 10y ago
  You're confusing quantum mechanics with quantum field theory. Pilot wave theory is just QM, although some field theory extensions have been discussed. There's no particular reason such an extension would be impossible.
lcvella 10y ago
For me, what is most important on the subject is that, even if we can't differentiate from one interpretation to another experimentally (yet), it doesn't mean they are all equally correct. Specifically in connection with general relativity, which is an open issue, the exploration of alternative interpretations of QM may lead to actual experiments differentiating one interpretation from another, effectively tuning it into a theory.
MichaelApproved 10y ago
Here's another great video from PBS Spacetime on this topic https://youtube.com/watch?v=RlXdsyctD50 https://youtube.com/watch?v=RlXdsyctD50 This channel and Sixty Symbols are awesome for insight into physics/quantum mechanics without the math.
rwallace 10y ago
The impression I have of pilot wave theories is that when you look closely at them, the pilot waves are doing basically all the work with the particles just along for the ride. At that point it's tempting to delete the particles and see what happens, and then when you give the result a fresh paint job it turns out to be isomorphic to the many worlds interpretation (or the Copenhagen interpretation if you take the computational step of not following branches that can no longer be significant to currently observed results). Am I missing something?
- Avshalom 10y ago
  It's important to remember that the math of quantum mechanics, the math people use to model and predict phenomena, the math thats given us transistors, lasers, quantum computing etc... That's all very accurate and extremely successful so anything that tries to explain why these models are the way they are is going to be pretty much the same as any other explanation if you tilt your head to the side and squint because they all have to produce the same very well specified set of mathematical models.
- qubex 10y ago
  What is truly irksome about this 'reformulation' is that the supposed Pilot Wave is presumably 'pushing ' on the billiard-ball-like elementary point-particles, but they are not able to "push back" on the Pilot Wave. The Pilot Waves of two particles are, however, assumed to interact between themselves in a manner that resembles the elementary interaction of the particles... and this is quite an extraordinary scenario, if you think about it. It's quite aether-like, and I mean that in a mildly derogatory manner. (IANAP)
snarfy 10y ago
Here is my theory. Someone smarter than me please prove me wrong. A particle's 'Zitterbewegung' motion generates wake fields in the vacuum energy, causing the particle to generate its own pilot wave as energy fluctuations in the vacuum. https://en.wikipedia.org/wiki/Zitterbewegung https://en.wikipedia.org/wiki/Zitterbewegung https://en.wikipedia.org/wiki/Vacuum_energy https://en.wikipedia.org/wiki/Vacuum_energy http://phys.org/news/2013-10-strange-behavior-pilot-wave-dynamics-action.html http://phys.org/news/2013-10-strange-behavior-pilot-wave-dyn...
jostylr 10y ago
I think the most problematic issues is that physicists reject the wave function. I have never understood this since if you reject the wave function in standard quantum mechanics, you have nothing left. But the pilot wave is just the wave function of quantum mechanics, albeit on a universal scale. It is in all the theories. And just because one has a "collapse", which is always approximate anyway (no delta functions for a position measurement, for example), one still has a wave function as the only object in standard QM and that is an expanding object defined on 3*number of particles in universe. But we do not experience that. We experience 3 dimensional space with rather point-like objects moving about. Pilot wave theory starts with "We have particles moving about. How do they move?" That's the question it starts with and it answers it in the simplest way possible given the wave function: the wave function tells the particles how to move using Bohm's equation which is a very easy thing to derive. Indeed, you can derive it even more quickly than Schrodinger's equation from the same basic facts of Einstein's light quanta hypothesis and de Broglie's hypothesis. It was a choice to inject mysticism into quantum mechanics. If you stick with trying to describe the evolution of particles, Bohm is natural. If you want to describe something else whose evolving configuration would give us our experience, then that is fine, but you have to say what that is. The standard interpretation does not as it is solely concerned with experiments and measurements with no definition of them in a fundamental way. It is more like they were trying to do regression fitting on experimental data without any understanding of what the underlying stuff was nor any interest in such a question. The other difficulty is spin. Spin is trivial if you put the spin degrees of freedom in the value space of the wave function. But many think of spin as real as position. It is not. It matters what the experiment is; the spin value for a particle is not defined independent of the experiment. Bohmian mechanics gives a theory while standard quantum mechanics gives a computational formalism. Depending on your goals, the latter can be sufficient. The former tells us why stuff happens and also allows us to derive that computational formalism.
lamontcg 10y ago
The biggest problem with pilot wave theory is that extending it to field theory hasn't been done (or at least there's several published formalisms with no approach that everyone agrees upon). Right now its useless for practical physicists at the LHC to compute anything about collisions. Its mathematically equivalent to the other mathematical formulations of QM, but the only utility it offers so far is entirely philosophical. And at some point physicists don't spend their entire lives noodling on the underpinnings of QM and need to move on and really try to compute the g-factor of the electron, or analyze the collision data coming out of the LHC. There needs to be a Lorentz invariant field theory model of pilot waves that can answer some question easier than the other mathematical formalisms for it to catch on.
vorotato 10y ago
I think the best answer would be, "If true it doesn't add anything new." At least given our current understanding. If some new discovery showed some measurable difference between the two interpretations then we'd have to actually decide.
vorotato 10y ago
I think the best answer would be, "If true it doesn't add anything new." At least given our current understanding. If some new discovery showed some measurable difference between the two interpretations then we'd have to actually decide.

119 points by rfreytag 10y ago

If you're interested in this sort of thing as a lay person (as I am), I would recommend the PBS Space Time YouTube channel. Be sure to stick around for the end of each video, as he often calls out comments on earlier videos that contain corrections or clarifications (in many cases, from _very_ highly qualified physicists and other subject matter experts). Here's their recent episode on pilot wave theory: https://www.youtube.com/watch?v=RlXdsyctD50 https://www.youtube.com/watch?v=RlXdsyctD50

mblaney 10y ago
Thanks for the video. He mentioned that the pilot wave is made up of "some stuff", but never got back to that being one of the unknowns of pilot wave theory. Seems like that questioned will need to be answered before it is taken more seriously.
- combatentropy 10y ago
  > He mentioned that the pilot wave is made up of "some stuff" Could the stuff be dark matter or dark energy?
  - naasking 10y ago
    Pilot waves aren't made of anything, they are a description of configuration space. Think of it like this: to describe particle motion, take the ordinary/classical equations of motion, and now add another term to account for quantum behaviour. The force exerted by this term at time t is a function of the position of every other particle in the universe at time t, no matter the distance. That's pilot wave theory, where this term is sometimes called the "quantum potential" and is governed by Schroedinger's equation. As you can see, this extra term goes to zero when quantum effects become negligible and we recover classical mechanics straight away. The difficulty is the obvious nonlocality and what that means for special relativity.
    - bmh100 10y ago
      Could this connection to the rest of the universe be considered conceptually similar to a form of entanglement?
      - naasking 10y ago
        Sort of. There is no real entanglement in this formalism, not in the way it's typically portrayed. I suppose you could say entanglement is there all the time. Macroscopic observation of entanglement via non-local correlations is really just a context in which we make the non-local connection observable.

lisper 10y ago

This is the bottom line: "It's been demonstrated experimentally that you can't have a local, deterministic, real, definite theory (i.e. that would lead to demonstrably false conclusions). People intuitively expect all of those things to be true, but we can prove that it isn't the case. The various interpretations all try to give up one of "local", real", "definite", or "deterministic" in order to preserve the others, thus preserving at least a modicum of their intuition. The pilot wave idea gives up on locality" And I will add: Multiple worlds gives up on definiteness. "Zero worlds" (my personal favorite) gives up on realism. And, of course Copenhagen gives up on determinism. Take your pick. Or go with decoherence, which kind of lets you turn a knob to give up a little bit of all four and dial in whatever setting you like.

phkahler 10y ago
But if someone makes a conscious choice to choose one that preserves locality, shouldn't they change their mind when "spooky action at a distance" starts happening? Non-locality is staring them in the face and they refuse to adopt a formalism that makes it explicit. They seem to like things that appear strange and non-intuitive.
- combatentropy 10y ago
  I agree. I thought that the scientific world already gave up on the idea of locality, since entanglement has been experimentally demonstrated. Furthermore, I don't have a problem with accepting non-locality from a theoretical perspective either, now that I know about the Holographic Principle. If the universe is a hologram, then the apparatus that is projecting the hologram can be connected in ways that aren't obvious in the hologram.
  - otakucode 10y ago
    It's not that kind of a hologram... all the hologram idea says is that all of the information in our universe can be represented on a 2 dimensional surface. It doesn't claim there is literally a hologram projector somewhere projecting a hologram of our universe. Such a thing would be nonsensical. If the projector were outside our universe it would, by definition, be causally disconnected from our universe and thereby never capable of influencing it in any way. If it were capable, it would, again by definition, be part of our holographic universe.

contravariant 10y ago

I would have though the fact that the pilot wave theory uses the (multi-particle) Schroedinger equation, while most modern physics is based on field theory, would be more important. So far I've seen no formulation of the pilot wave theory in a way that incorporates fields, or provides some other mechanism to account for things like the annihilation of particles.

dnautics 10y ago
If I'm not mistaken, It's just formalism. Mathematically a continuous wave function is equivalent to a countably infinite vector space. It can be hard to switch between the two (as a chemist we are taught Schroeder and I have a hard time wrapping my head around Heisenberg)
- chestervonwinch 10y ago
  > a continuous wave function is equivalent to a countably infinite vector space I think you mean that the function is a point in the vector space. More precisely, it is a point in a particular separable Hilbert space, i.e., a complete vector space equipped with an inner product that has countable, dense basis.
  - dnautics 10y ago
    right, sorry. The space of continuous wave functions are equivalent to a countably infinite vector space.
naasking 10y ago
There are plenty of field theory extensions for Bohmian mechanics. Due the relatively few people working on it, no single approach has become dominant.
jostylr 10y ago
There are various versions, but the one I recommend to date loses determinism (that was never the point) and allows for annihilation and creation of particles: https://arxiv.org/abs/quant-ph/0208072 https://arxiv.org/abs/quant-ph/0208072 In addition, the ideas of Bohmian mechanics has led to a new direction in dealing with the divergences in QFT, that is, in finding a version of it that is mathematically well-defined: https://arxiv.org/abs/1506.00497 https://arxiv.org/abs/1506.00497

tzs 10y ago

Would this be kind of the physics equivalent of nonstandard analysis in mathematics? Nonstandard analysis (NSA) is an approach to analysis that essentially makes rigorous the vague notions of infinitesimals that Newton and Leibniz and the other pioneers of calculus based their work on. Newton's fluxions and Leibniz's differentials provided great guidance, and in a lot of cases they even worked and gave correct results, but they were not really rigorously defined, and later mathematicians started running into serious problems with that approach. Those were resolved with the approach that we all now known and love (loath?): limits and the epsilon/delta approach to them. NSA extends the real field to contain a new kind of number that is positive but is less than 1/N for any integer N, giving a new field called the hyperreals. You can then do things like define the derivative of f at x to be (f(x+h)-f(x))/h where h is an infinitesimal, work out that using ordinary algebraic manipulations, and then just drop any terms that are infinitesimal. NSA goes far beyond just calculus. You can use these ideas all through analysis. Seems pretty cool, and a lot clearer than a limits approach. So why has it not taken over? I believe that a big part of it is that it has been shown that NSA and standard analysis are equivalent. Anything that you can prove in one can be proven in the other. Perhaps more important, one doesn't seem any better than the other at leading to deep insights. If you can't solve a problem in standard analysis, you probably aren't going to figure out the solution if you use NSA, and vice versa. So while it might be overall nicer if we were starting from scratch to use NSA instead of standard analysis everywhere, so much is already done in standard analysis that switching now would be too painful.

millstone 10y ago
Interesting analogy but I'm not sure if it holds. Infinitesimals are an alternative to the limit-based formalism typically seen. It changes the way you do calculus. However Bohmian Mechanics is a different interpretation, not a different formalism. You can accept the interpretation, but you still end up solving the Schrödinger equation in the same way, using the same mathematical methods. The analogy works better for matrix mechanics as compared to Schrödinger's wave mechanics. These are mathematically quite different even though they give the same results.
- jayajay 10y ago

phkahler 10y ago

Since the pilot wave theory is deterministic, wouldn't someone be able to simulate a quantum computer with a classical one in reasonable time and storage?

otakucode 10y ago
What would make you think that? Deterministic doesn't imply predictable, reducible, or low complexity. Even a purely deterministic simple system can be capable of (and most are) chaotic behavior whose information content would grow faster than any system smaller than itself could predict. In other words, the only way to "simulate" the system would be to completely reproduce every bit of it, and let it evolve in realtime. And practically speaking, we can't even approach that.
- jayajay 10y ago
  For example, the double pendulum: https://en.wikipedia.org/wiki/Double_pendulum https://en.wikipedia.org/wiki/Double_pendulum. That said, the phase space of a double pendulum is bounded.
  - duckingtest 10y ago
    It's really funny that something as simple is impossible to predict over longer times, because you would need perfect information. Yet climate science is 'settled'.
    - jayajay 10y ago
      Take an undamped double pendulum and divide the space up into 2 sections. Suppose you can only check which section the pendulum is every N seconds. Every time you check, you record the value, and over time you build up a sequence of K numbers: 1,0,1,0,0,1,1,1,1,0,0,1,0,... Suppose you know the exact initial state (dx/dt, x) of the pendulum. What bounds on K and T are required such that the sequence of numbers is asymptotically indistinguishable from a purely random sequence? So, because of a silly thought experiment, one might think there is very simple order to the apparent randomness. But, as Pauli would say, "it's not even wrong"...

ClayFerguson 10y ago

There is one other interpretation of Pilot Wave theory that is sort of the "inverse" of Pilot Wave. and to me makes more sense. The PW may be correct but the particles are not following a wave that is moving around them. What is happening is that each particle is 'emitting' (spherically and radially outward from itself) a wave of its own. It is the interaction of all other waves that cause the particle to move. Just like a particle with mass distorts the spacetime around it, in a 'static way', perhaps charged particles distort spacetime in a way that is directly tied to the speed of light, and thus distort spacetime in a 'dynamic way'. But the fact that the slit experiment "works" even when we know only a single particle at a time is being sent thru, it just makes more intuitive sense that the particle is neither interacting with itself, nor with other universes (copies of itself). So what i'm saying is PW theory is FAR more intuitive than Copenhagen many-worlds to me. I believe there is genuinely one particle going thru the slit experiment when we think there is, and it follows the path thru in a way that is statistically determines much more by a PW-type theory than any other theory.

scythe 10y ago

I have a fond memory of taking an advanced (graduate) seminar class with taught by one of the oldest professors at my university -- and attended by another. The lecturer was describing something to do with manifolds and various obscure formulations of classical field theories and he mentions that he was at a lecture once where someone had related this theory to Bohmian mechanics -- the other professor cut him off "It's wrong" A student held up his hand and asked what Bohmian mechanics was. Before the lecturer could answer "Don't worry, it's wrong" It was difficult to contain myself.

dmichulke 10y ago
Related: http://www.phdcomics.com/comics.php?f=1912 http://www.phdcomics.com/comics.php?f=1912

bicubic 10y ago

There's one major shortcoming that the answer doesn't seem to touch on: pilot wave theory doesn't explain relativity whatsoever, while quantum field theory does. We've experimentally confirmed relativity, so at best, pilot wave theory is incomplete.

naasking 10y ago
You're confusing quantum mechanics with quantum field theory. Pilot wave theory is just QM, although some field theory extensions have been discussed. There's no particular reason such an extension would be impossible.

lcvella 10y ago

For me, what is most important on the subject is that, even if we can't differentiate from one interpretation to another experimentally (yet), it doesn't mean they are all equally correct. Specifically in connection with general relativity, which is an open issue, the exploration of alternative interpretations of QM may lead to actual experiments differentiating one interpretation from another, effectively tuning it into a theory.

MichaelApproved 10y ago

Here's another great video from PBS Spacetime on this topic https://youtube.com/watch?v=RlXdsyctD50 https://youtube.com/watch?v=RlXdsyctD50 This channel and Sixty Symbols are awesome for insight into physics/quantum mechanics without the math.

rwallace 10y ago

The impression I have of pilot wave theories is that when you look closely at them, the pilot waves are doing basically all the work with the particles just along for the ride. At that point it's tempting to delete the particles and see what happens, and then when you give the result a fresh paint job it turns out to be isomorphic to the many worlds interpretation (or the Copenhagen interpretation if you take the computational step of not following branches that can no longer be significant to currently observed results). Am I missing something?

Avshalom 10y ago
It's important to remember that the math of quantum mechanics, the math people use to model and predict phenomena, the math thats given us transistors, lasers, quantum computing etc... That's all very accurate and extremely successful so anything that tries to explain why these models are the way they are is going to be pretty much the same as any other explanation if you tilt your head to the side and squint because they all have to produce the same very well specified set of mathematical models.
qubex 10y ago
What is truly irksome about this 'reformulation' is that the supposed Pilot Wave is presumably 'pushing ' on the billiard-ball-like elementary point-particles, but they are not able to "push back" on the Pilot Wave. The Pilot Waves of two particles are, however, assumed to interact between themselves in a manner that resembles the elementary interaction of the particles... and this is quite an extraordinary scenario, if you think about it. It's quite aether-like, and I mean that in a mildly derogatory manner. (IANAP)

snarfy 10y ago

Here is my theory. Someone smarter than me please prove me wrong. A particle's 'Zitterbewegung' motion generates wake fields in the vacuum energy, causing the particle to generate its own pilot wave as energy fluctuations in the vacuum. https://en.wikipedia.org/wiki/Zitterbewegung https://en.wikipedia.org/wiki/Zitterbewegung https://en.wikipedia.org/wiki/Vacuum_energy https://en.wikipedia.org/wiki/Vacuum_energy http://phys.org/news/2013-10-strange-behavior-pilot-wave-dynamics-action.html http://phys.org/news/2013-10-strange-behavior-pilot-wave-dyn...

jostylr 10y ago

I think the most problematic issues is that physicists reject the wave function. I have never understood this since if you reject the wave function in standard quantum mechanics, you have nothing left. But the pilot wave is just the wave function of quantum mechanics, albeit on a universal scale. It is in all the theories. And just because one has a "collapse", which is always approximate anyway (no delta functions for a position measurement, for example), one still has a wave function as the only object in standard QM and that is an expanding object defined on 3*number of particles in universe. But we do not experience that. We experience 3 dimensional space with rather point-like objects moving about. Pilot wave theory starts with "We have particles moving about. How do they move?" That's the question it starts with and it answers it in the simplest way possible given the wave function: the wave function tells the particles how to move using Bohm's equation which is a very easy thing to derive. Indeed, you can derive it even more quickly than Schrodinger's equation from the same basic facts of Einstein's light quanta hypothesis and de Broglie's hypothesis. It was a choice to inject mysticism into quantum mechanics. If you stick with trying to describe the evolution of particles, Bohm is natural. If you want to describe something else whose evolving configuration would give us our experience, then that is fine, but you have to say what that is. The standard interpretation does not as it is solely concerned with experiments and measurements with no definition of them in a fundamental way. It is more like they were trying to do regression fitting on experimental data without any understanding of what the underlying stuff was nor any interest in such a question. The other difficulty is spin. Spin is trivial if you put the spin degrees of freedom in the value space of the wave function. But many think of spin as real as position. It is not. It matters what the experiment is; the spin value for a particle is not defined independent of the experiment. Bohmian mechanics gives a theory while standard quantum mechanics gives a computational formalism. Depending on your goals, the latter can be sufficient. The former tells us why stuff happens and also allows us to derive that computational formalism.

lamontcg 10y ago

The biggest problem with pilot wave theory is that extending it to field theory hasn't been done (or at least there's several published formalisms with no approach that everyone agrees upon). Right now its useless for practical physicists at the LHC to compute anything about collisions. Its mathematically equivalent to the other mathematical formulations of QM, but the only utility it offers so far is entirely philosophical. And at some point physicists don't spend their entire lives noodling on the underpinnings of QM and need to move on and really try to compute the g-factor of the electron, or analyze the collision data coming out of the LHC. There needs to be a Lorentz invariant field theory model of pilot waves that can answer some question easier than the other mathematical formalisms for it to catch on.

vorotato 10y ago

I think the best answer would be, "If true it doesn't add anything new." At least given our current understanding. If some new discovery showed some measurable difference between the two interpretations then we'd have to actually decide.

vorotato 10y ago