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B Photon producing Electron-Positron pair's effect on c.

  1. Jul 29, 2017 #1
    Hello all, disclaimer here, I haven't taken quantum mechanics yet, all I know of it comes form books and PBS Space Time Series.

    Since a photon can, at any given instant, "split" into an Electron-Positron pair, does it mean that if this occurs between point a and b, the measured speed o that photon would be lower than c? Because Electrons and Positrons cannot travel at c.
    Thus, this effect would be magnified over large distances, as the photon would have many chances to split and recombine.
    I still know little about the process, maybe because they are virtual particles this doesn't apply or something...
  2. jcsd
  3. Jul 30, 2017 #2


    Staff: Mentor

    its a common misconception bought about by reading lay textbooks on QFT. Its not really true - so don't draw and conclusions from it.

    It comes from interpreting in a heuristic way Feynman diagrams, But Feynman diagrams are pictorial representations of a so called Dyson Series:

    These ideas of splitting, positrons are electrons travelling back in time (that one is really a bit silly, it would also mean electrons are positrons travelling back in time - but its a heuristic picture we are stuck with), etc, are simply heuristics drawn from the diagrams - they sometimes help in solving and understanding problems- but are in fact wrong.

  4. Jul 30, 2017 #3


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    You cannot understand photons without studying relativistic QFT. Photons are so far from anything we are used to in everyday experience that it is impossible to adequately speak about them in a non-mathematical way! Without math a lot of quantum physics is not communicable in an adequate way, and photons are among these topics.
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