Packets of Light
Einstein instantly appreciated Plank’s discovery of quantization. He later called it “the basis of all 20th century research in physics.”
“Without this discovery, it would not have been possible to establish a workable theory of molecules and atoms and the energy processes that govern their transformations. Moreover, it has shattered the whole framework of classical mechanics and electrodynamics and set science a fresh task: that of finding a new conceptual basis for all of physics.” ~ Albert Einstein
In 1905, addressing classical physics’ inability to explain the photoelectric effect, Einstein argued that radiant energy consisted of quanta.
“The energy of a light ray is not continuously distributed over an increasing space but consists of a finite number of energy quanta which are localized at points in space, which move without dividing, and which can only be produced and absorbed as whole units.” ~ Albert Einstein*^
(The photoelectric effect is the glow of objects when absorbing radiation. Electrically charged particles, either electrons or ions, are emitted when a body takes on energy.)
(American chemist Gilbert N. Lewis termed these packets of light photons in 1926.)
Echoing Plank’s equation, Einstein’s formula for photonic energy was: E = hf, where E is the energy of light at frequency f, tempered by Planck’s action quantum (h).
Einstein generalized the quantum hypothesis in 1907 by using it to interpret the temperature-dependence of the specific heats of solids. As a follow-on, Einstein treated thermodynamic fluctuations in two 1909 papers. Though he did not use the word duality or make any assertion of principle, Einstein introduced wave/particle duality into physics. This was one of several instances where Einstein failed to appreciate the implications of his assertions.
“The theory of relativity has changed our view of the nature of light insofar as it does not conceive of light as a sequence of states of a hypothetical medium, but rather as something having an independent existence just like matter.” ~ Albert Einstein in 1909