[Physics] Are all positrons electrons traveling back in time

quantum-electrodynamics

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 an element, such as Fludeoxyglucose (18F) emit these positrons so much more than other elements?

Thanks a bunch! I hope I was clear with my question, if not please let me know.

-Eric

Best Answer

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. This states can be obtained from the vacuum state by acting with creation operators.

This 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.