Michael Netzer

Thanks, ydoaPs.

In pair production, the emergence of positrons and electrons from a photon striking an atom nucleus, it's calculated that mass-energy equivalence creates the e-e+ from the photon's energy if it's at least 1.022 MeV by applying E=MC^2. I understand the mass of e-e+ and the energy of the photon. But it's not clear to me from what or where C^2 is derived. Where from do we calculate the speed of light squared in the photon's interaction with an atom nucleus? Many thanks in advance for any help.