From mcnees@mastodon.social on Mastodon: Even in 1913, when Einstein was nominated for membership in the Prussian Academy, Planck's letter of support admitted that Einstein "might sometimes have overshot the target in his speculations, as for example with the light quantum hypothesis." But evidence continued to mount. Finally, Compton's 1923 result treating X-rays as massless particles in relativistic collisions with electrons gave irrefutable evidence and convinced most of the remaining skeptics.