Albert Einstein’s paper explaining the photoelectric effect is received by Annalen der Physik.

Albert Einstein submitted his paper explaining the photoelectric effect to the journal Annalen der Physik, marking one of the key publications of his 1905 “Annus Mirabilis.” The paper, titled “Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt” (“On a Heuristic Point of View Concerning the Production and Transformation of Light”), was received by the journal on that date and later published on 09/06/1905. At the time, Einstein was working as a technical expert at the Swiss Patent Office in Bern. In the paper, he proposed that light could be understood not only as a wave but also as consisting of discrete packets of energy, which he called “light quanta.” Building on Max Planck’s 1900 introduction of energy quanta in blackbody radiation, Einstein suggested that electromagnetic radiation itself is quantized. He argued that the energy of each quantum is proportional to the frequency of the light, expressed by the relation E = hν, where h is Planck’s constant and ν is frequency. Einstein’s explanation addressed experimental findings showing that when light shines on certain metals, electrons are ejected only if the light’s frequency exceeds a specific threshold, regardless of intensity. Classical wave theory could not account for why increasing brightness failed to eject electrons below that frequency. Einstein’s model predicted that the kinetic energy of emitted electrons depends directly on the light’s frequency, a relationship later confirmed experimentally, notably by Robert A. Millikan in experiments conducted between 1912 and 1915. Although the concept of light quanta was initially met with skepticism, Einstein’s theoretical framework became foundational to quantum physics. In 1921, he was awarded the Nobel Prize in Physics “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.” The prize citation specifically referenced this 1905 work rather than his theory of relativity. The receipt of Einstein’s manuscript by Annalen der Physik on 18/03/1905 marked the beginning of the formal scientific record of the light quantum hypothesis, which would become central to the development of quantum mechanics in the decades that followed. #AlbertEinstein #PhotoelectricEffect #QuantumPhysics #AnnusMirabilis #HistoryOfScience