16 ms·

As far as I understand – and Wikipedia seems to support this – pilot wave theory, or actually any hidden variable theory, or actually any interpretation of Quan

by sampo 10y ago

As far as I understand – and Wikipedia seems to support this – pilot wave theory, or actually any hidden variable theory, or actually any interpretation of Quantum Mechanics, they are different mathematical models that produce exactly the same predictions for experimental outcomes. https://en.wikipedia.org/wiki/Pilot_wave https://en.wikipedia.org/wiki/Pilot_wave So how can, even in theory, any experiment support one interpretation any more or less than all the others?

jessriedel 10y ago
They can't. The article is grossly misleading.
ewjordan 10y ago
You're 100% correct - this is merely a direct presentation of the weirdness that results if you choose to interpret this experiment in the language of pilot wave theory. The physical results are the same as you would predict using normal methods, and as such it's a real stretch to consider this experimental support for Bohm's interpretation.
- dandelany 10y ago
  One thing I've never been clear on is whether this is empirically the case, or theoretically the case. That is to say, is it theoretically possible that someday we may find evidence that supports Bohm's interpretation and falsifies the others? Or are they truly mathematically equivalent theories?
  - jldugger 10y ago
    My layman's understanding of is that fundamental uncertainty can't really be distinguished from a hidden variable we cannot observe or influence.
    - eru 10y ago
      Alas, it's a bit more complicated than that.
  - ewjordan 10y ago
    If memory serves, as far as classical quantum mechanics goes, Bohm's interpretation is 100% mathematically equivalent to the standard interpretation, making it observationally impossible to distinguish the two (much like many worlds vs. Copenhagen). It would be in extensions to the theory where things might differ, though I don't know much about attempts to extend pilot wave theory to QFT.
    - SEMW 10y ago
      > Bohm's interpretation is 100% mathematically equivalent to the standard interpretation, making it observationally impossible to distinguish the two This is not quite correct. It is mathematically equivalent to Copenhagen only at times of 'quantum equilibrium', which is when ρ = φ² (probability density is the square of the wavefunction). Copenhagenists call this the Born rule and treat it as axiomatic. Bohmians don't since they don't need to, since in Bohmian mechanics a system which is not in quantum equilibrium will evolve to be in quantum equilibrium in a very very short time. Which gives a way to empirically distinguish pilot-wave theory if the universe began in quantum non-equilibrium. (We have no reason to think it did, but we have no reason to think it didn't, so, shrug). If it did, the early universe would have evolved differently in the first femtosecond after the big bang, which should theoretically be detectable to us by analysis of CMB anisotropies. This has been worked on: a friend of mine did a masters project which among other things involved porting some simulation code on very-early-universe numeric simulations under quantum non-equilibrium (IIRC from fortran 77 to fortran 95, because physicists), under Mike Towler.
- goldenkey 10y ago
  I'm just going to leave these links for those as curious as I was: https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox [Video: The pilot-wave dynamics of walking droplets] https://www.youtube.com/watch?v=nmC0ygr08tE https://www.youtube.com/watch?v=nmC0ygr08tE
Ygg2 10y ago
There may be consequences of each different interpretation, that might leave it open to different results in some conditions. I remember Many World theory claiming there would be some unexplained signals in cosmic background radiation.
- LoSboccacc 10y ago
  Iirc pilot wave theory better explain wave/particle duality but afaik there isn't yet a theoretical experiment I know of which could tell it apart from the current theory.
pjs_ 10y ago
That's correct. If we knew of an experimental technique to distinguish interpretations of quantum mechanics we would be in a much better place than we are now. This article is a classic of article titles stretching science journalism, stretching the press release, stretching the paper, stretching the basic result.
alpineidyll3 10y ago
As usual a completely inaccurate and oversold misinterpretation of quantum mechanics.
tagrun 10y ago
You (and everyone who replied you so far) misunderstood: if you read the article, you'll see that this is not the issue. This is about the reality of trajectories built-into the pilot wave theory (such a concept which doesn't even exist in "text-book" interpretation of quantum mechanics, which says particles don't have positions or trajectories until you measure them, upon which they "decide" their position through an "artificial" process called wavefunction collapse; notably, as of now, wavefunction collapse and the reality of wavefunction is still a subject of debate). There was a paper "Surrealistic Bohm Trajectories" which argued that trajectories predicted by pilot wave theory don't make any sense as real trajectories in general, hence these "trajectories" cannot correspond to real trajectories. A careful analysis which properly takes the nonlocality into account shows the flaw in their argument (arXiv:quant-ph/0010020, omitted in the text linked), and this is the corresponding experiment which confirms their analysis (using weak measurements on a pair of entangled photons to sketch "average" trajectories in a WWM setup). If you like, this is about the interpretation of a concept within an interpretation. While I agree that the title is a little bit flashy, experimental confirmation for the reality of Bohmian trajectories is an important topic.
- grkvlt 10y ago
  Surrealistic Bohm Trajectories is referenced in the article, as the ESSW paper, after the authors. Here is the PDF link: http://www.degruyter.com/dg/viewarticle.fullcontentlink:pdfeventlink/$002fj$002fzna.1992.47.issue-12$002fzna-1992-1201$002fzna-1992-1201.pdf/zna-1992-1201.pdf?t:ac=j$002fzna.1992.47.issue-12$002fzna-1992-1201$002fzna-1992-1201.xml http://www.degruyter.com/dg/viewarticle.fullcontentlink:pdfe...
  - deleted 10y ago
    [deleted]
  - tagrun 10y ago
    No, I meant arXiv:quant-ph/0010020

by sampo 10y ago

jessriedel 10y ago

They can't. The article is grossly misleading.

ewjordan 10y ago

You're 100% correct - this is merely a direct presentation of the weirdness that results if you choose to interpret this experiment in the language of pilot wave theory. The physical results are the same as you would predict using normal methods, and as such it's a real stretch to consider this experimental support for Bohm's interpretation.

dandelany 10y ago
One thing I've never been clear on is whether this is empirically the case, or theoretically the case. That is to say, is it theoretically possible that someday we may find evidence that supports Bohm's interpretation and falsifies the others? Or are they truly mathematically equivalent theories?
- jldugger 10y ago
  My layman's understanding of is that fundamental uncertainty can't really be distinguished from a hidden variable we cannot observe or influence.
  - eru 10y ago
    Alas, it's a bit more complicated than that.
- ewjordan 10y ago
  If memory serves, as far as classical quantum mechanics goes, Bohm's interpretation is 100% mathematically equivalent to the standard interpretation, making it observationally impossible to distinguish the two (much like many worlds vs. Copenhagen). It would be in extensions to the theory where things might differ, though I don't know much about attempts to extend pilot wave theory to QFT.
  - SEMW 10y ago
    > Bohm's interpretation is 100% mathematically equivalent to the standard interpretation, making it observationally impossible to distinguish the two This is not quite correct. It is mathematically equivalent to Copenhagen only at times of 'quantum equilibrium', which is when ρ = φ² (probability density is the square of the wavefunction). Copenhagenists call this the Born rule and treat it as axiomatic. Bohmians don't since they don't need to, since in Bohmian mechanics a system which is not in quantum equilibrium will evolve to be in quantum equilibrium in a very very short time. Which gives a way to empirically distinguish pilot-wave theory if the universe began in quantum non-equilibrium. (We have no reason to think it did, but we have no reason to think it didn't, so, shrug). If it did, the early universe would have evolved differently in the first femtosecond after the big bang, which should theoretically be detectable to us by analysis of CMB anisotropies. This has been worked on: a friend of mine did a masters project which among other things involved porting some simulation code on very-early-universe numeric simulations under quantum non-equilibrium (IIRC from fortran 77 to fortran 95, because physicists), under Mike Towler.
goldenkey 10y ago
I'm just going to leave these links for those as curious as I was: https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox [Video: The pilot-wave dynamics of walking droplets] https://www.youtube.com/watch?v=nmC0ygr08tE https://www.youtube.com/watch?v=nmC0ygr08tE

Ygg2 10y ago

There may be consequences of each different interpretation, that might leave it open to different results in some conditions. I remember Many World theory claiming there would be some unexplained signals in cosmic background radiation.

LoSboccacc 10y ago
Iirc pilot wave theory better explain wave/particle duality but afaik there isn't yet a theoretical experiment I know of which could tell it apart from the current theory.

pjs_ 10y ago

That's correct. If we knew of an experimental technique to distinguish interpretations of quantum mechanics we would be in a much better place than we are now. This article is a classic of article titles stretching science journalism, stretching the press release, stretching the paper, stretching the basic result.

alpineidyll3 10y ago

As usual a completely inaccurate and oversold misinterpretation of quantum mechanics.

tagrun 10y ago

You (and everyone who replied you so far) misunderstood: if you read the article, you'll see that this is not the issue. This is about the reality of trajectories built-into the pilot wave theory (such a concept which doesn't even exist in "text-book" interpretation of quantum mechanics, which says particles don't have positions or trajectories until you measure them, upon which they "decide" their position through an "artificial" process called wavefunction collapse; notably, as of now, wavefunction collapse and the reality of wavefunction is still a subject of debate). There was a paper "Surrealistic Bohm Trajectories" which argued that trajectories predicted by pilot wave theory don't make any sense as real trajectories in general, hence these "trajectories" cannot correspond to real trajectories. A careful analysis which properly takes the nonlocality into account shows the flaw in their argument (arXiv:quant-ph/0010020, omitted in the text linked), and this is the corresponding experiment which confirms their analysis (using weak measurements on a pair of entangled photons to sketch "average" trajectories in a WWM setup). If you like, this is about the interpretation of a concept within an interpretation. While I agree that the title is a little bit flashy, experimental confirmation for the reality of Bohmian trajectories is an important topic.

grkvlt 10y ago
Surrealistic Bohm Trajectories is referenced in the article, as the ESSW paper, after the authors. Here is the PDF link: http://www.degruyter.com/dg/viewarticle.fullcontentlink:pdfeventlink/$002fj$002fzna.1992.47.issue-12$002fzna-1992-1201$002fzna-1992-1201.pdf/zna-1992-1201.pdf?t:ac=j$002fzna.1992.47.issue-12$002fzna-1992-1201$002fzna-1992-1201.xml http://www.degruyter.com/dg/viewarticle.fullcontentlink:pdfe...
- deleted 10y ago
  [deleted]
- tagrun 10y ago
  No, I meant arXiv:quant-ph/0010020