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The Bottom Line on QM

  1. Jan 13, 2005 #1
    The Sept 04 issue of Scientific American contains an article called "Was Einstein Right?" which deals with that question in relation to quantum mechanics. The following is from that article:

    "Instead of presuming to reconstruct the theory from scratch, why not take it apart and find out what makes it tick. That is the approach of Fuchs and others in the mainstream of studying the foundations of quantum mechanics.

    They have discovered that much of the theory is subjective: it does not describe the objective properties of a physical system but rather the state of knowledge of the observer who probes it. Einstein reached much the same conclusion when he critiqued the concept of quantum entanglement--the "spooky" connection between two far-flung particles. What looks like a physical connection is actually an intertwining of the observer's knowledge about the particles. After all, if there really were a connection, engineers should be able to use it to send faster than light signals, and they can't. Similarly, physicists had long assumed that measuring a quantum system causes it to "collapse" from a range of possibilities into a single actuality. Fuchs argues that it is just our uncertainty about the system that collapses."

    So there we have it - the leading expert on the foundation of QM says that "spooky action at a distance" is not really a physical connection. Also, the "collapse of the wave function" is not physically real. The fact is that QM is not a description of reality. Even Bohr agreed with Fuchs when he said "THERE IS NO QUANTUM WORLD."

    "I've said it before, I'll say it again:
    Can a dog collapse a state vector?
    Dogs don't use state vectors.
    I myself didn't collapse a state
    vector until I was 20 years old."
    - Christopher A. Fuchs

    All the best
    John B.
  2. jcsd
  3. Jan 13, 2005 #2
    The real question is not what Fuchs think that QM is not the real question is what he thinks the world is! I assume hes not a fan of local-realism(?) Then whats his explanation to the "spooky action at a distance"?

    If theres no collapse in the wavefunction then what the hell is going on?? The only thing that I can think of that solves all theese problems is if all of this, the universe, me and you and this computer is just a prerecording that we somehow believe that we can affect.

    Bye bye free will
  4. Jan 13, 2005 #3
    I'm sure Chris would agree that he is not THE leading expert on quantum foundations, but it is true to say that he is one of the most noisy ones.

    I actually quite like his approach, even if I don't agree with him on the interpretational consequences of it. The debate actually goes all the way back to classical probability. Philosophers, mathematicians, statisticians and physicists have been debating whether classical probabilities should be regarded as objective or subjective for years. In my view, the subjective (or Bayesian) approach is the better one for foundational questions, although some problems in statistics are better solved by more traditional methods.

    Now, if you agree that the Bayesian approach is better for classical probabilities, there is no reason why you shouldn't try to apply it to quantum probabilities as well. It gives a new take on the OPERATIONAL foundations of quantum theory, in my view superior to other operational approaches. This is no small achievement, but I don't think it really addresses the main problems of interpretation (e.g. nonlocality, Kochen-Spekker, etc.) at least not yet. However, what it does achieve is to give us a new language to address these questions in.

    Therefore, I think if you look at Chris Fuchs' foundational research papers, and try to strip out the rhetoric, what you end up with is a rather elegant and insightful approach to quantum mechanics.
  5. Jan 13, 2005 #4


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    All this just goes to show that Fuchs doesn't understand the EPR argument (and same for Bohr). If the collapse of the wave function involves merely an updating of our knowledge of distant systems (as opposed to the view that our measurement actually physically affects that distant system) then evidently there was some fact about that distant system which could not be inferred from the pre-measurement wave function. Or, as Podolsky wrote, there is an "element of reality" for that distant system which has no counterpart in the quantum description -- i.e., QM is incomplete and we should start looking for a so-called hidden variable theory instead.

    If wave function collapse describes a change in physical reality, quantum mechanics is nonlocal. If, on the other hand, wave function collapse describes merely a change in knowledge, quantum mechanics is incomplete. That's the EPR dilemma. It is disturbing that so-called experts on the foundations of QM have, for 70 years, failed to grasp this simple argument.

    Or maybe the answer (to EPR) that Fuchs and Bohr had in mind wasn't merely that wf collapse describes a change in knowledge, but, rather, that QM doesn't provide a description of reality *at all*. But then, what the hell are these guys doing arguing that QM is "complete"? What in the world does it mean for a theory to be a complete description of reality, if it isn't supposed to describe reality at all, or if there *is* no such thing as reality???

    Unless one wants to literally deny that there is a physical world out there (and I can think of no stupider thing for a *physicist* to believe!), one is simply stuck with the EPR dilemma: either QM fails to provide a complete description of that world, or the theory (and the world) are nonlocal.

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