My teacher told me that Photons are elastic particles (allegedly it was a postulate of Max Plancks's Quantum theory too) and that during the photoelectric effect due to "elastic collision" the transfer of energy occurs simultaneously which results in the ejection of electrons without a time delay. I now know that there is in fact a time delay, something my high textbook also missed out on. In addition, I also figured out that the collision cannot be elastic as the sum of the Kinetic Energy is not a constant like it must be for elastic collision, with work energy being the culprit.
But that gets me back to the original question. Are photons elastic particles? What about electrons? Can elasticity be defined for particles like photons and electrons? A recent research appears to think so.
When one snooker ball hits another, both spring away from each other in an elastic manner. In the case of two photons a similar process -- the elastic collision -- has never been observed. Physicists have now shown, however, that such a process does not only occur, but even could soon be registered in heavy-ion collisions at the LHC accelerator.
But what I came to the conclusion in the first paragraph and what was found by researchers don't seem to be compatible. Is there a reason? My best guess would be that the photons appear elastic only during photon-photon interactions but not during photon-electron interactions.