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Quantum leap FTL ?

  1. Sep 9, 2007 #1
    Various quantum states are described as existing in one state or another, but nothing in between. A simplified example is an electron moving from one shell to another. When that electron transfers from one orbit to another does the electron not exist for a period of time or is the transfer instantaneous so the electron effectively changes location faster the speed of light?

    I understand this question is complicated by the uncertainty principle and it impossible to assign a precise location and momentum to the electron at any given moment. However, I hope you understand the essence of the question, which is do quantum leaps happen at a mundane speed of light pace (where the electron is not in a quantum state for a brief but finite period) or literally instantaneously?
    Last edited: Sep 9, 2007
  2. jcsd
  3. Sep 9, 2007 #2


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    It's my understanding that quantum leaps are considered to be instananeous, and would violate the prohibition against superluminal travel if they fit into the normal definition of the word "travel". (Because an electron moves from one orbital to another without ever passing through the space in between, it is never really "moving" FTL)

    If it is true that the electron changes location without travelling through space, then the instantaneous nature of tis relocation becomes more intuitively understandable, since time and space are itnerdependant. An object that travels through no space does not need to travel through time, either. This is simply to say that the object has not moved through spacetime.
  4. Sep 9, 2007 #3
    What changes instantaneously in such a process is the electron's energy. But, energy levels in an atom are not equivalent to discrete orbits. I realize that many text books use the image of the Bohr model to explain the idea of energy levels; but, this is quite simply a bad picture.

    For any given energy level in the atom, there is a wavefunction, which (essentially) describes the probability of finding an electron with that given energy (and angular momentum) at each point in space, from the center of the nucleus to the ends of the universe (in the limit that nothing else exists). In any given level there very few points where that probability is zero. Thus, you can think that in a certain sense, no matter what level you are in, the electron is pretty much everywhere. Then, when you change states, the only thing that changes is to what extent the electron is at each point.
  5. Sep 9, 2007 #4
    Quantum leaps are instantaneous. They happen in a mathematical model, not necessarily in real time and space. Quantum states (in the defacto standard interpretation of the theory) are not real states. It should also be noted that the geometrical (spacetime) interpretation of relativity theory (which, if you like, can be used to justify some weird and unobserved effects, is not necessarily a description of real time and space ... descriptive interpretations associated with both quantum theory and relativity theory are probably gross oversimplifications of what the physical world is really like).

    So, none of this possibly weird or paradoxical stuff that the models might allow to happen (like instantaneous quantum leaps) should be fretted over, because none of it is happening in the real world of our experience.

    You might think of an instantaneous quantum leap as a place where you can substitute "we don't know what happens in the real physical world at this point". Come to think of it you can substitute the previous quote for much of quantum theory ... and as long as you keep that in mind, then you won't be unduly trouble by quantum paradoxes. The theory is about preparations and observed effects (ie., emitters and detectors), and has very little, if anything in most cases, to say about what might be happening in between.

    Since there's no way to verify that instantaneous quantum effects are happening in the real physical world, they will forever remain in the realm of purely speculative or metaphysics.
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