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Virtual Particles

  1. Jan 7, 2010 #1
    Can electrons, or other real particles for that matter, interact with virtual particles?

    Do virtual particles ever come into existence in between the electron's energy levels of an atom? Is there actually a vaccum between electron energy levels of an atom or is this an abstract representation?

    Lastly, do virtual particles come into existence in solid matter in the vacuum between atoms and molecules?

    I am a little sketchy on how a guage field jumps from one electron to another and what that really means. Is it possible that an electron moves from point A to point B not by classical momentum, but by a series of state transitions resulting from interaction with a field of virtual particles in which the start and ending state of the transition is an electron? So really the electron isn't really moving, but being destroyed and recreated in new positions until it reaches point B.
  2. jcsd
  3. Jan 7, 2010 #2
    Virtual particles is a concept that comes into play in calculations in quantum field theory. They refer to the intermediate states, which you sum over when you compute stuff like transition amplitudes or the vacuum energy. They are a reflection of the math that comes into play. They are not physical; they are a mathematical tool. You just use them to compute physical quantities: the quantum amplitudes.

    If you can find a way to compute quantum amplitudes non-perturbatively, then the term virtual particles never comes into play. You wouldn't need to use Feynman diagrams, as the intermediate states do not appear. But keep in mind that there is no one who knows how this can be done. For most quantum field theories we simply do not know how we can compute stuff non-perturbatively. Perturbation theory is the _only_ tool we have for these theories, so we always have to deal with Feynman diagrams.

    As a counterexample, conformal field theory is a quantum field theory where you do not use Feynman diagrams. Instead, other mathematical tools are available. Therefore the concept of a virtual particle doesn't exist in conformal field theories, because you do not use the Feynman diagram-method.

    But if you work with a theory that makes use of Feynman diagrams, then you will deal with virtual particles or intermediate states. In this perspective, you could say that particles interact with virtual ones, but you should keep in mind that this is just a statement about the type of math you are using. There is no a virtual particle popping in and out of existence.

    Solid matter is just a collection of a large number of particles. The same physical rules apply, so you will also deal with Feynman diagrams and virtual particles.

    As for your final question: in quantum mechanics the propagation of a particle is determined by a summation over all possible ways in which a particle can move from one point to another. So both the the processes you mention contribute to this process. But again, this is only a statement about the math we use to determine this process in the first place. It does not mean that this is what physically is happening.
  4. Jan 7, 2010 #3
    This clears things up some for me. Thanks for the response.
  5. Jan 7, 2010 #4
    Vacuum polarization, a virtual electron-positron pair (Feynman bubble diagram), can shift the strength of the Coulomb field near a nucleus. For this reason, the energy of many pionic and muonic atom energy levels (binding energies) are often shifted by up to ~1%.
    Bob S
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