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  1. 12 Sep '14 15:29 / 3 edits
    http://phys.org/news/2014-09-fluid-mechanics-alternative-quantum-orthodoxy.html

    personally, although I am uncertain of the validity of the pilot-wave interpretation of quantum mechanics, I still favour it over the Copenhagen interpretation which I think is erroneous in its logic (don't have a problem with something being causeless. Just think we should be very cautious not to automatically assume the no known cause means simply no cause! ) .
    I favour virtually any realist interpretation of quantum mechanics over the Copenhagen interpretation and the pilot-wave interpretation is just one of the realist interpretations.
  2. Standard member DeepThought
    Losing the Thread
    12 Sep '14 16:48
    Originally posted by humy
    http://phys.org/news/2014-09-fluid-mechanics-alternative-quantum-orthodoxy.html

    personally, although I am uncertain of the validity of the pilot-wave interpretation of quantum mechanics, I still favour it over the Copenhagen interpretation which I think is erroneous in its logic (don't have a problem with something being causeless. Just think we should be ve ...[text shortened]... gen interpretation and the pilot-wave interpretation is just one of the realist interpretations.
    Interesting that in their fluid model the bit of fluid that bounces around bounces around on a surface just short of having waves on it when the particle is absent but waves appear when the droplet is present. This is strongly reminiscent of vacuum polarisation in quantum field theory.

    The problem with the Copenhagen interpretation is that it doesn't say anything. It essentially denies the reality of, well, reality. I think it is overly influenced by continental idealist philosophy and gives "conscious" observers too much of a role. Also it relies on a set of observations that can't be made. One makes a momentum measurement which exactly determines the momentum of a particle how exactly? Detectors in particle physics experiments determine the momentum of a particle by measuring the length of the ionisation trail it leaves in a detector. This is not a single observation. There is a similar problem with position measurements. What one sees then is a cascade of electrons caused by the interaction of the incoming particle with an electron in the detector. So what one measures is the position of the scattered electron, not of the actual particle which in principle could be half way across the universe (in practice not as the probability of interaction goes down as 1/r^2 for electromagnetically mediated interactions).

    The problem I have with the pilot wave interpretation is that one has the wavefunction as the pilot wave and the particle guided through it. But everything in the theory is written down in terms of the wave. Including interactions. In order to make a measurement one has to have some kind of interaction. But that interaction is governed by the wave and not the particle. So all one ever sees is the wave and one never sees the particle. So what is the point of the particle?

    John Bell was of the opinion that pilot wave theory was identical to the many universes interpretation and I think he is right. The piloted particle (piloton?) is a marker to tell you where the particle "really" is and fulfills the same role as the partitioning of the wavefunction of the universe in the many universes interpretation.

    John Bell wrote an excellent book (actually a collection of his papers on this subject) called "Speakable and Unspeakable in Quantum Mechanics" which as these things go is accessible, at least to the regular posters in this forum. I strongly recommend it.
  3. 12 Sep '14 18:31
    Originally posted by DeepThought
    I think it is overly influenced by continental idealist philosophy and gives "conscious" observers too much of a role.
    I wasn't aware that any serious physics gave conscious observers any role whatsoever, whether put in quotes or not. I always thought that was a deliberate misunderstanding by theists eager to stroke their egos.
    My understanding of quantum mechanics is that interactions between particles rules out possible pasts. Whether or not all possible pasts exist, or whether we simply cannot identify which past was the 'real' one, was, I thought, the issue with different schools of thought on quantum mechanics.
  4. 12 Sep '14 19:24
    The Copenhagen interpretation does not (necessarily) involve a conscious observer, although it sweeps the possibility that wavefunction collapse is an emergent property of a system under the rug rather carelessly.
  5. 12 Sep '14 21:45 / 4 edits
    Originally posted by KazetNagorra
    The Copenhagen interpretation does not (necessarily) involve a conscious observer, although it sweeps the possibility that wavefunction collapse is an emergent property of a system under the rug rather carelessly.
    agreed.

    Just consider Brownian motion for an analogy: apparent random motion with no visible cause and yet we know there are invisible atoms colliding with the visible particles to cause that apparent motion. Why cannot apparently causeless random quantum events be like that? -at the very least it is not possible to ever rule that possibility out.
  6. Standard member DeepThought
    Losing the Thread
    12 Sep '14 22:09
    Originally posted by twhitehead
    I wasn't aware that any serious physics gave conscious observers any role whatsoever, whether put in quotes or not. I always thought that was a deliberate misunderstanding by theists eager to stroke their egos.
    My understanding of quantum mechanics is that interactions between particles rules out possible pasts. Whether or not all possible pasts exist, o ...[text shortened]... he 'real' one, was, I thought, the issue with different schools of thought on quantum mechanics.
    I'd have to look up who it was who talked about conscious observers, as I remember it it was one of the big names in the US and a little later than Bohr. Implicitly it is there in the Copenhagen interpretation - if there is an observer then since they are observing they must be conscious. In Schrödinger's cat experiment it is Schrödinger who has the ability to collapse the wave function of his cat because of his big primate brain and not the cat who just can't tell if it's alive or not. It is one of the bigger problems of the Copenhagen interpretation that it requires conscious observers.
  7. 13 Sep '14 06:50
    Originally posted by DeepThought
    I'd have to look up who it was who talked about conscious observers, as I remember it it was one of the big names in the US and a little later than Bohr. Implicitly it is there in the Copenhagen interpretation - if there is an observer then since they are observing they must be conscious. In Schrödinger's cat experiment it is Schrödinger who has the ab ...[text shortened]... ne of the bigger problems of the Copenhagen interpretation that it requires conscious observers.
    I think its just confusion brought in by the use of the word 'observer' when in reality 'interaction' is the correct term. And no, it is not Schrödinger nor his brain that collapses the wave function. It is the interaction between the inside of the box and the outside of the box. Schrödinger's brain is totally irrelevant.

    The Wikipedia page says:
    Although the Copenhagen interpretation is often confused with the idea that consciousness causes collapse, it defines an "observer" merely as that which collapses the wave function.
  8. Standard member DeepThought
    Losing the Thread
    13 Sep '14 19:44
    Originally posted by twhitehead
    I think its just confusion brought in by the use of the word 'observer' when in reality 'interaction' is the correct term. And no, it is not Schrödinger nor his brain that collapses the wave function. It is the interaction between the inside of the box and the outside of the box. Schrödinger's brain is totally irrelevant.

    The Wikipedia page says:
    [qu ...[text shortened]... ses collapse, it defines an "observer" merely as that which collapses the wave function.[/quote]
    No, interactions do not cause wavefunction collapse. Otherwise either you'd never be able to set up an entangled state or you'd need to invent some reason why some interactions do collapse wavefunctions and others don't.

    I think the claim that an observer is any piece of equipment would not be agreed to be all physicists (certainly not this one). Suppose we attempted to do the EPR experiment and used photographic film to detect the photon after it's gone through some polaroid, then, until the experimenter has looked at it, the film is in a superposition of states. If the polaroid counts as an observer then it shouldn't be.
  9. 14 Sep '14 06:59 / 1 edit
    Originally posted by DeepThought
    No, interactions do not cause wavefunction collapse. Otherwise either you'd never be able to set up an entangled state or you'd need to invent some reason why some interactions do collapse wavefunctions and others don't.

    I think the claim that an observer is any piece of equipment would not be agreed to be all physicists (certainly not this one). Su ...[text shortened]... lm is in a superposition of states. If the polaroid counts as an observer then it shouldn't be.
    The simplest definition of "observer" is just "that which makes the wavefunction collapse." But this begs the question: what makes a wavefunction collapse? Sometimes it is defined more precisely as "an interaction with a macroscopic object", but that is not very precise either.
  10. 14 Sep '14 07:08
    Originally posted by DeepThought
    No, interactions do not cause wavefunction collapse.
    Yes, they do. By definition.

    Otherwise either you'd never be able to set up an entangled state or you'd need to
    invent some reason why some interactions do collapse wavefunctions and others don't.

    An entangled state is a state in which interactions with the outside world have not yet taken place.

    I think the claim that an observer is any piece of equipment would not be agreed to be all physicists (certainly not this one).
    I am surprised. I thought the error was mostly by laymen. So it seems physicist make the same error too.

    Suppose we attempted to do the EPR experiment and used photographic film to detect the photon after it's gone through some polaroid, then, until the experimenter has looked at it, the film is in a superposition of states.
    Only from the experimenters perspective. From the Polaroids perspective, the image was captured immediately. But since the Polaroid is interacting with other parts of the world, you are actually wrong about the need for the experimenter to look at the film. Suppose we set up a computer to observe the film. The computer, on seeing the photons image on the film, feeds your cat. You later observe the film and see the photon was detected. Your claim is that until you observed the film, the Polariod was in a superposition of states and your cat was both fed and unfed. That is clearly nonsense.

    If the polaroid counts as an observer then it shouldn't be.
    It seems you too are suffering from an ego problem. There is nothing special about consciousness that it somehow has magical effects on physics. Would you also claim that until you have observed the experimenters brain, his brain is also in a superposition of states? If not, why not?
  11. 14 Sep '14 07:14
    Originally posted by twhitehead
    Yes, they do. By definition.
    No, one can write down a Hamiltonian with interactions and solve the time evolution for the system (in certain cases) deterministically without invoking wavefunction collapse.
  12. 14 Sep '14 13:41
    Originally posted by KazetNagorra
    No, one can write down a Hamiltonian with interactions and solve the time evolution for the system (in certain cases) deterministically without invoking wavefunction collapse.
    Are you saying that two particles interact, but their positions or velocities (at the time of interaction) are not known more accurately after the interaction than before?
  13. 14 Sep '14 15:09
    Originally posted by twhitehead
    Are you saying that two particles interact, but their positions or velocities (at the time of interaction) are not known more accurately after the interaction than before?
    Perhaps an instructive example is the hydrogen atom. In a hydrogen atom, the proton and the electron are interacting all the time (it's the electromagnetic interaction that keeps the atom together), but the wavefunction is not collapsing.
  14. Standard member DeepThought
    Losing the Thread
    14 Sep '14 16:03
    Originally posted by twhitehead
    Yes, they do. By definition.

    [b]Otherwise either you'd never be able to set up an entangled state or you'd need to
    invent some reason why some interactions do collapse wavefunctions and others don't.

    An entangled state is a state in which interactions with the outside world have not yet taken place.

    I think the claim that an observer is an ...[text shortened]... served the experimenters brain, his brain is also in a superposition of states? If not, why not?
    Do you think all entangled particles are primordial? To prepare an entangled state one has to interact with it in the first place. A decay generating two entangled photons involves an interaction. The atom couples with the electromagnetic field.

    It is not an error to dispute that a piece of equipment does not count as an observer. What Wikipedia says is the opinion of the last person who edited it. The polaroid is the piece of film that polarizes the light, it is not the film recording the event. The photographic film does not have a perspective, it is a piece of film. Saying it's macroscopic is no good, why do you think macroscopic objects are not subject to quantum theory? You can set up a macroscopic quantum state with a superconductor.

    For clarity I do not agree with the Copenhagen interpretation, but if one is using that then von Neumann's Conscious observers are necessary as it is the only place where the wavefunction can collapse. My feeling is that the correct interpretation has to do with emergent property of systems that Kazet alluded to above. But you dismiss the notion that consciousness is involved at your peril. You are arguing with Johnny von Neumann he was a smart guy and you might want to think twice about what you are saying.
  15. 14 Sep '14 17:55
    Originally posted by KazetNagorra
    Perhaps an instructive example is the hydrogen atom. In a hydrogen atom, the proton and the electron are interacting all the time (it's the electromagnetic interaction that keeps the atom together), but the wavefunction is not collapsing.
    Yes, the atom as a whole is a closed system.