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Head to https://squarespace.com/physicsexplained to save 10% off your first purchase of a website or domain using code PHYSICSEXPLAINED Everyone is taught that Einstein introduced the idea of light quanta (photons) to explain the photoelectric effect, but that is not how the idea was born. This video starts with the blackbody radiation crisis and the ultraviolet catastrophe, then follows Planck’s quantisation and Einstein’s 1905 thermodynamic argument about what radiation entropy is really counting. From Wien’s law and Boltzmann’s principle, the light quantum emerges naturally and the photoelectric equation becomes a sharp prediction, later confirmed by Millikan. References Einstein, A. (1905). Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt. Annalen der Physik. https://doi.org/10.1002/andp.19053220607 Einstein, A. (1905). Concerning an Heuristic Point of View Toward the Emission and Transformation of Light (English translation). https://inters.org/files/einstein1905_photoeff.pdf Norton, J. D. (2006). Atoms, Entropy, Quanta: Einstein’s Miraculous Argument of 1905. https://sites.pitt.edu/~jdnorton/papers/miraculous.pdf Klein, M. J. (1963). Einstein’s First Paper on Quanta. In The Natural Philosopher, Vol. 2, pp. 59–86. Blaisdell Publishing Company, New York. https://www.informationphilosopher.com/solutions/scientists/klein/Klein-Einstein-Light-Quanta.pdf Pais, A. (1982). Subtle is the Lord: The Science and the Life of Albert Einstein. Oxford University Press. https://global.oup.com/academic/product/subtle-is-the-lord-9780192806727 Stuewer, R. H. (2006). Einstein’s Revolutionary Light-Quantum Hypothesis. Acta Physica Polonica B 37(3). https://s3.cern.ch/inspire-prod-files-4/447e0b45371520bcc94f20a762d35407 🤝 Support the channel Patreon → https://www.patreon.com/physicsexplained 🔗 Follow me Instagram → https://www.instagram.com/physics_explained_ig X (Twitter) → https://twitter.com/PhysicsExplain1