See the Breit-Wheeler process, wherein two gamma photons are converted into an electron and a positron via a process that's the reverse of electron-positron annihilation. I do not doubt this process. However I'm less confident about the Wikipedia two-photon physics article. It talks about gamma-gamma pair production, and as far as I know it's in line with what some particle physicists say. It says this:
"From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes[clarification needed]. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple".
However as far as I know, a 511keV photon does not spend its life magically morphing into a 511keV electron and a 511keV positron. That’s in breach of conservation of energy. In similar vein the electron and the positron cannot then magically morph back into a single 511keV photon. That's in breach of conservation of momentum. Moreover photons travel at the speed of light whilst electrons and positrons do not - a photon cannot spend its life fluctuating into fermion pairs, if it did it couldn't travel at c. Besides, virtual particles are virtual. As in not real. They aren't short-lived real particles that pop in and out of existence like magic. Instead they only exist in the mathematics of the model. Which is why hydrogen atoms don’t twinkle, and magnets don’t shine. On top of all that pair production surely does not occur because pair production occurred. Spontaneously. Like worms from mud. All in all, this explanation for pair production is woefully inadequate. A better explanation is required. So:
How does gamma-gamma pair production really work?
I will give a 500-point bounty to the least-worst answer to the question. One answer will get the bounty, even if I don't like it.
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