Photons

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This book examines the gradual development of the concept of ‘light quanta’ or ‘photons,’ a term used since 1926. The various synonyms employed by physicists reflect diverse mental models of what light quanta represent: Are they finite, quantized energy packets or bullets of light? Atoms or molecules of light? Light corpuscles or quantized waves? Singularities or spatially extended structures capable of interference? The notion of ‘light quantum’ first appeared in Einstein’s 1905 paper addressing the photoelectric effect, but its conceptual history predates and extends beyond that year. Some semantic layers trace back to Newton and Kepler, while others emerged or faded over time. The book explores six distinct mental models of light quanta and presents two historiographic approaches to concept formation: the author’s model of conceptual development as semantic accretions and Mark Turner’s model of conceptual blending. Both models are shown to be valuable for understanding this complex topic. This work represents a historiographically sophisticated exploration of the fully developed concept and its twelve semantic layers, integrating the history of science, terminology, and a philosophically informed history of ideas, alongside insights from cognitive science.