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Quantum determinacy

  1. Jun 14, 2004 #1
    I have been told that radioactive decay, photon emission and absorption, and other such subatomic events are not deterministic. That besides leaving no clue as to when the event--say, decay--will take place, QM also has found that there IS NO initiating process that kicks off the event. In other words, decay events are uncaused. This, of course, goes beyond the mere inability to predict an event, but speaks to a very fundamental, and exceptionally unique character the subatomic world.

    My question then, is: Are such events at the subatomic level, such as radioactive decay, truly without cause, or is it still simply a matter of we don't or can't know the cause?
  2. jcsd
  3. Jun 15, 2004 #2


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    The 'S' in LASER stands for stimulated. I had always heard that, while sometimes an atom will emit a photon spontaneously, an atom can also be induced (or 'stimulated') to emit a photon. Still, that leaves an interesting class of phenomena that truly appear to be without an initiating process, as you put it. Einstein sure thought there was an as-yet undetermined underlying cause, but I think his point of view is a minority one among physicists.
  4. Jun 15, 2004 #3
    All I can say is there is absolutely no reason for anything in the quantum world aside from what WE give it. So say a light beam takes two paths to two detectors before reaching only one and disappearing from the other. There was no reason for it to choose any one path. This means there was no cause and we could not predict it. But why can't it always go down one path by being random instead of interchanging? This would mean that if it did go down one path all the time WE could predict it. There would be a cause (but there isn't one - we only think there is. So somehow by viewing which path the light went down meaning WE think the light went down causes the light to go down the other path just to contradict our meaningful observation such that we could not predict it, and there would then be no reason which would contradict our common sense.
  5. Jun 15, 2004 #4
  6. Jun 17, 2004 #5
    Is Stimulated Emission Deterministic?

    while sometimes an atom will emit a photon spontaneously, an atom can also be induced (or 'stimulated') to emit a photon.

    If I understand correctly, this is also a statistical thing. Under the right conditions, the number of atoms that emit photons will be higher than you would normally expect, so we say that some fraction of the radiation is "stimulated". But I don't think you can point to one particular atom and say, 'that one radiated spontaneously', and 'that other one was stimulated'. You can't even predict beforehand which ones will emit at all.
    Last edited: Jun 17, 2004
  7. Jun 18, 2004 #6
    It is true that we cannot say when an atom will emit a photon, because it is a statistical process. However, the photons atoms emit stems from the excitation of electrons into higher "orbits". We can see if the atom has a free lower "orbit" and so it is a matter of time when the electrons jumps.

    We cannot see on an atom if it was stimulated or spontaneously excited.

    I firmly believe that this uncertainty is a truly fundamental part of our universe.
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