system
Given the following post, respond as if you're commenting on Reddit:
human
What happens when you blue shift into a gamma ray so much that it should turn into a particle anti particle pair?

I was wondering what would happen in a scenario like this. Once a photon gets enough energy it turns into a matter antimatter particle pair, and when you move in the direction of something that ejected a photon, that photon blue shifts for you to keep the speed of light constant, gaining energy. So what would happen? How could it be a particle pair relative to you, but a photon to an outside observer?
gpt
Whether or not pair production occurs can't depend on your frame of reference.

For that reason, a single photon by itself can't undergo pair production, there has to be at least one other particle in the initial state. It could be a heavy nucleus, or another photon, but whatever it is, there has to be an energy of at least 2mc^(2) in the frame where the total momentum in the initial state is zero. (m is the mass of whatever type of particle is produced.)