Can pair production take place in a vacuum?

Answer 1

== No. In a complete vacuum with nothing there, electromagnetic energy (the gamma ray from which pair production might arise) will proceed unaffected and at the speed of light. The question asks specifically about a vacuum and suggests that there is nothing there to in any way react with the gamma ray. So the answer is that pair production will not take place in, say, the extreme vacuum of deep space where a gamma ray is passing. If we start "tinkering" with the scenario and, say, firing high energy gamma rays down an evacuated pipe through which we pass a magnetic field, pair production might then occur. But it is impossible to have a magnetic field without having the material to create it - moving charges. No moving charges, no magnetic field, no pair production. Pair production will not arise spontaneously from a gamma ray of sufficient energy to facilitate it, and this is almost certainly what the question is asking. Additional information There has been publication of research that suggests that a magnetic field can initiate pair production, but the investigation continues, and the idea of doing this "strays" from what is arguably the true intent of the question. It would have been easy to change the question, but why not leave up what is up? The idea that a magnetic field can initiate pair production is an interesting one.