I have recently read Richard Feynman's "QED" and in it Feynman describes positrons as 'how we view electrons when they are going back in time and we are stuck traveling forwards in time'. I was wondering, are all positrons electrons traveling back in time? Or can you have an electron with a positive charge (positron) that is not traveling backwards? Furthermore, if all positrons are (from a quantum dynamics standpoint) traveling backwards in time, then why (again from a quantum dynamics standpoint) would a chemical, such as Fluorodeoxyglucose (18F) emit these positrons so much more than other chemicals?


1 Answer 1


It is an analogy made for the wide audience. The actual picture provided by QFT is far more technical.

Configurations of electrons and positrons are states of the quantum system, called the electron field. These states can be obtained from the vacuum state by acting with creation operators.

These creation operators evolve in time (in Heisenberg picture), and the their frequency is positive for electrons and negative for positrons (or vice versa, it doesn't matter).

The whole thing is even more complicated in QED, when the interaction affects properties like mass, charge or field normalization factor via the renormalization.

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    $\begingroup$ Thanks for the explanation, I'm still in high school so I suppose I just need to wait until I've taken all the formal classes before I start thinking too abstractly. $\endgroup$
    – Eric
    Commented Nov 3, 2014 at 16:55
  • $\begingroup$ It sounds depressing, but I think you are right :) Good luck! $\endgroup$ Commented Nov 3, 2014 at 16:58

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