# Re: pair production

Suppose a positron/electron pair were produced in a vacuum chamber with a very strong magnetic field, so strong that the particles circle around and meet after, say, 3 ns. Would the particles annihilate, or would they not due to the positron existing in backward time? That is, when occupying the same point in space, the electron would do so at +3 ns, the positron at -3 ns, and they would be "separated" by 6 ns.

• Antiparticles evolve in normal time. You are stretching a shared metaphor on virtual particles best forgotten in this context. Jul 11 '17 at 18:57

The problem is that the pair cannot be produced in vaccum, because of conservation laws. The gamma has to hit something. The gamma has zero mass , and in the system of the hypothetical pair, the invariant mass of the added four vectors of the e+e- would be at least 2x$m_e$.