I Can Photons from Distant Quasars Decay into Particle Pairs in Vacuum?

[intervoxel]

When a photon emitted by a distant quasar arrives, almost certainly has an energy less than 1.02 MeV. If it had a higher value, it likely would have decayed into particle pairs on its way to the Earth. Is this reasoning correct?

 

[George Jones]

By conservation of energy/momentum, a single, isolated photon cannot decay. If a photon decayed into an e- e+ pair, there would be frame in which the pair has zero spatial momentum, but there is no frame in which a photon has zero spatial momentum.

 

[ZapperZ]

When a photon emitted by a distant quasar arrives, almost certainly has an energy less than 1.02 MeV. If it had a higher value, it likely would have decayed into particle pairs on its way to the Earth. Is this reasoning correct?

Please note that in all e-p pair production that we have experimentally done, the energetic photons must pass through a material made up of heavy elements (eg: Mo solid) to get any substantial probability to create such e-p pair. As has been stated, there is a conservation of momentum issue of a photon spontaneously transforming into e-p pair in vacuum. A "heavy" object must be nearby to take up the momentum transfer, thus the use of such heavy material to create e-p pairs.

This has been covered already in many previous threads, such as these:

https://www.physicsforums.com/threa...of-momentum-vs-conservation-of-energy.664025/
https://www.physicsforums.com/threads/pair-production-and-gamma-ray.849809/
https://www.physicsforums.com/threa...ron-and-positron-from-isolated-photon.748000/
https://www.physicsforums.com/threads/pair-production-and-another-body.140600/

Zz.