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B Wave Function Collapsing Function

  1. Apr 29, 2017 #1
    Is there a function that describes the collapsing of a wave function? Or does in happen instantaneously in theoretical terms. I do want to know what happens with the other possible states, whether they stay alive but in another form, or what's going on.
     
  2. jcsd
  3. Apr 29, 2017 #2

    Nugatory

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    There is no function describing collapse; and for that matter, collapse doesn't even appear in the mathematical formulation of the theory so there are no "theoretical terms" for describing it.

    As for what's "going on"? The theory obstinately refuses to say anything about that. It tells us the probability of getting a particular measurement result given the wave function; and it tells us what the wave function will be after we've gotten a particular measurement result; but says nothing about how we get from the pre-measurement state to the post-measurement state.
     
  4. Apr 29, 2017 #3
    So it's just a measure of probability, and not an actual physical thing. Not a superimposed state in "real" terms?
     
  5. Apr 29, 2017 #4

    Nugatory

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    That's too strong of a statement. The thing that we know for sure is that you can use the mathematical machinery of quantum mechanics, including the wave function, to predict with exquisite accuracy how the world works. That fact is not obviously inconsistent with the wave function being "real", but it it is also not obviously inconsistent with the wave function not being "real".

    You might want to search this forum for more of the 83 bazillion or so threads about interpretations of quantum mechanics that we have.
     
  6. Apr 30, 2017 #5

    vanhees71

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    Well, I think sqljunkey is on a very right track! If you think his statement over, i.e., "So it's [the quantum state, i.e., statistical operator] just a measure of probability, and not an actual physical thing." and finally accept it you save a lot of time to do the really interesting things with quantum theory instead of mulling about the never solvable philosophical problems some people have with it. There will never be a consensus about these issues, because it doesn't belong to objective science but to personal believes. E.g., I don't think that one needs a collapse but that the assumption of a collapse is full of problems contradicting basic principles of physics. You don't need a collapse as soon as you have accepted that Born's Rule, i.e., the probabilistic (and only probabilistic) meaning of the quantum state, as a fundamental postulate to define the theory.

    Whether the state is "real" is a question that cannot be answered, because there is no scientifically sound definition of the meaning of "real" in this context. When do you call a mathematical construct real? Are the coordinates of the Earth to describe its motion around the Sun real? Are electromagnetic fields real? Are the fiber bundles real that build the basis of the description of this field as a gauge field real? I have no clue, what these questions mean, let alone what a useful answer may be! All I know is that all these mathematical constructs lead to an amazingly detailed description by relatively few basic concepts (if I have to name one basic concepts then it's group theory to describe symmetries).
     
  7. May 3, 2017 #6

    DrClaude

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    The OP was answered long ago. Time to close this thread.
     
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