Pilot-wave hydrodynamics (Quantum phenomena in macroscopic hydrodynamic systems)(thales.mit.edu)

90 pointsby peter_d_sherman4 days ago3 comments

isoprophlex3 days ago
I thought the images were old school POVRay renders. Turns out they have a visualisation setup, and they're real pictures!
Video:
https://gfm.aps.org/meetings/dfd-2015/55f71c7b69702d060d7505...
Paper:
https://thales.mit.edu/bush/wp-content/uploads/2017/01/GFM-P...
- cubefox3 days ago
  I guess you mean "real photographs".
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- sheepscreek3 days ago
  Wow that is incredible. I believe the colors are overlaid (or underlaid) to help with illustration but the position/placement is a real photograph.
  - zardo2 days ago
    It's in the video, they've just framed up the shot to see the reflection of what looks like a piece of paper with colored stripes printed on it.
aggrrrh3 days ago
It's a real shame that de Broglie Bohm theory gets so little attention compared with the mainstream interpretation.
- quantum_mcts3 days ago
  The whole idea of Bohmian mechanics is to preserve the notion of « classical trajectory » while trying to cover existing experimental evidence for QM. I was a fan of it ant the University - but slowly realised that the strategy seems to be just add the classical-limit consequences of the QM as extra postulates. And even that approach faced larger and larger obstacles - like fermions statistics, the QFT with creation / annihilation of particles, spinor fields requiring Grassmanian « classical trajectories » and the whole thing still requires preferred reference frame - in obvious contradiction with basic SR.
  This whole story is very similar to attempts of physics fringe to preserve the notion of « aether » while satisfying the experimental evidence for SR.
  - zmgsabst3 days ago
    Relativistic aethers are called fields — and are mainstream.
    Aether theories (in addition to providing the inaccessible preferred frame needed here) also simplify two issues with relativity:
    - what frame does a photon have?
    - what conveys gravitational wave memory to future particle trajectories?
    In aether theories, photons correspond to the aether frame. But that gets set to nulls in relativity, which is a theory of sub-luminal perspectives.
    (I suspect you knew all that, but other readers may not.)
    quantum_mcts3 days ago
    Yeah, and the fact that this type of guys coalesce around Bohmian mechanics topics sealed the deal for me....
  - _bobm3 days ago
    What do you think about the efforts of Hiley and Denis [1], which may suggest that the pilot wave may be a manifestation, a mathematical projection, of a deeper physical process which hierarchically gives way to the pilotwave, particles, like a coordinati9n space.
    [1] https://www.mdpi.com/2073-8994/16/1/67
    westurner3 days ago
    I have GrC(2,4) with E_rel=0 against Pilot-Wave in the double-slit and n-slit here: https://github.com/westurner/sustainablefactory/blob/main/do... :
    > 3.1 Why Real Positive Gr≥0(2,4) Crossing Minors Have a 50 Unphased Error—and How Complex GrC(2,4) Eliminates It
    > 3.2 Master Table: Five-Model Double-Slit Superposition & Relative Predictive Error
    They were talking about modeling orbits with Keplerian gravity and I mentioned that GrC(2,4) does seem to fit QED scattering gravity also with zero error. This is the extent of the peer review this far: https://news.ycombinator.com/item?id=50289590#50295549
    quantum_mcts3 days ago
    Skimmed the paper briefly. Looks like reformulation of single-particle QM with no new predictions. Most importantly (and as I mentioned above) doesn’t address particle creation and annihilation, which is where Bohmian-style approaches usually struggle.
    Authors seem to be aware of that, but make a weird tap-dance around the problem throughout the paper, seemingly scared to even "Voldmort" it. In that context, citing 1930 Dirac paper is laughably ironic.
  - anonymonynominoa day ago
    You dont need a preferred reference frame, you just need to fix a gauge. None of your predictions will depend on the "preferred" frame. its just a matter to make calculations. You have the same issue in many worlds for example when you want to do relativistic stuff.
- fpoling3 days ago
  Bohm interpretation is not compatible with relativity. One can argue that Copenhagen interpretation is also not compatible, but then from practical purposes both interpretations are equivalent and predict the same results so why bother with changing explanations when the new one still does not address the fundamental problem.
  - anonymonynominoa day ago
    Bohmian mechanics is just as compatible with relativity as many-worlds or whatever else you want is. That means, depending on how esoteric a space time you want to allow it might be hard, or it can be very well be done. If you can for example foliate the space time via Cauchy surfaces, then you can easily propagete with these surfaces as the spacial frame. Of course, the equations may depend on the frame, but the predictions are independent of the frame. Which should be familiar to anybody who did gauge theories.
  - _bobm3 days ago
    One can argue it gives better ontology of what is going on, but shifts the burden further into what the pilot wave is. And this actually is far more complicated maybe than QM itself.
    fpoling3 days ago
    Transactional interpretation of quantum mechanics is compatible with relativity and it is it that deserves more attention than Bohm interpretation. Unfortunately it uses a terminology like retrocasuation which sounds even stranger than how Copenhagen interpretation explains QM. So as long as experimental predictions stays the same I see little chances that transactional or similar interpretations will offset Copenhagen mainstream.
    _bobm3 days ago
    Interesting. I will take a look. I am not familiar.
- amelius3 days ago
  What is the propagation speed of this pilot wave?
  EDIT: ok, I asked AI and this speed is infinite, which is why the theory doesn't mesh well with relativity.
  - pja3 days ago
    Quantum effects travel instantaneously in standard QM, no pilot wave required: What’s limited to light speed is /information/.
    You can entangle two particles in QM, separate them by light years & when you measure the state of one of them you will instantaneously determine the state of the second one, no matter how far away it is. But you cannot transfer information by doing so - information must plod along at light speed between the two.
    quantum_mcts3 days ago
    First of all, your example doesn’t show any «instantaneous travel». You can shuffle two playing cards, send them by light years. Flip one of them and instantaneously determine what on the other one.
    There are more complicated correlations in QM than cannot be explained by hidden variables - but those are still correlations and, analogously, don’t imply any «instantaneous travel»
    pja2 days ago
    Flipping one card doesn’t change the state of the other one. Measuring the state of one of a pair of entangled particles does change the other one & that change appears to be instantaneous. We know this - Aspect carried out the experiment in the early 80s & those results have been confirmed by later, larger scale experiments.
    (IIRC It’s possible that a super-deterministic hidden variable system could explain Aspect’s results. But that pretty much requires the universe to deliberately plot against you, which seems very unlikely.)
    tome2 days ago
    > Flipping one card doesn’t change the state of the other one
    Right, but you didn't say "change" you said "determine".
    > Aspect carried out the experiment in the early 80s
    I have a write up of the maths behind this if anyone is interested, accessible to an undergraduate: https://h2.jaguarpaw.co.uk/posts/bells-theorem-made-simpler/
    fpoling3 days ago
    This notion of instantly getting knowledge hides the weirdness of QM. It is not surprising that when one reads a note from a box one instantly can get the knowledge about events in a distant galaxy. What is really weird with Copenhagen interpretation is that content of the note about what happens in a distant galaxy is not determined until the observer looks at it.
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