Here's how it went down:
* The Photoelectric Effect: Scientists had observed that shining light on certain metals caused electrons to be emitted. The puzzling thing was that the energy of the emitted electrons didn't depend on the intensity of the light, but rather on its frequency.
* Einstein's Explanation: Einstein proposed that light wasn't a wave, but rather a stream of tiny energy packets he called "light quanta" or "photons." He suggested that each photon carried a specific amount of energy proportional to its frequency. When a photon strikes a metal, it can transfer its energy to an electron, causing it to be ejected.
* Experimental Confirmation: Later experiments by Robert Millikan in 1916 and others confirmed Einstein's explanation and his proposed relationship between the energy of a photon and its frequency (E = hν, where E is energy, h is Planck's constant, and ν is frequency).
So, Einstein didn't directly prove that light travels in the form of photons. His explanation for the photoelectric effect, which was later verified by other experiments, became a foundational piece of evidence supporting the idea of light quanta, later known as photons.
It's important to note that the wave-particle duality of light is still a fundamental concept in physics. While photons are discrete packets of energy, light also exhibits wave-like properties, such as diffraction and interference.
