"My favorite deep, elegant and beautiful explanation is Albert Einsteins 1905 proposal that light consists of energy quanta, today called photons. Actually, it is little known, even among physicists, but extremely interesting how Einstein came to this position. It is often said that Einstein invented the concept to explain the photoelectric effect. Certainly, that is part of Einsteins 1905 publication, but only towards its end. The idea itself is much deeper, more elegant and, yes, more beautiful."
A photon is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can only move at one speed, the speed of light measured in a vacuum. The photon belongs to the class of boson particles.
"The theory of the light quantum, which Einstein initiated in 1905 and which is with us still, is certainly the most revolutionary development in the history of physics and arguably in the history of science. The creators of the theory, men such as Einstein, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, Wolfgang Pauli, and Paul Dirac, were often struck by the apparent "absurdity"—the utterly noncommonsensical aspects—of the world depicted by the quantum theory."
"Light is something like raindrops—each little lump of light is called a photon—and if the light is all one color, all the "raindrops" are the same."