For nearly two decades, almost nobody other than Einstein believed in photons. Even Planck himself didn’t think his work suggested that light was made of particles (though, years later, Planck’s work was hailed as the start of the quantum revolution). Only when Arthur Compton actually caught photons in the act of bouncing off of electrons, in 1923, did the physics community finally come around to Einstein’s way of thinking—and even then there were a few holdouts.
