The nature of light was the subject of one of the greatest debates in the history of physics. Isaac Newton, backed by his immense prestige, held that light was made of tiny “corpuscles” fired from luminous sources. Christiaan Huygens instead proposed that light was a wave propagating through a medium, like sound in air (Simonyi 2012, ch. 3).
The debate seemed to be settled in 1801, when the English physician Thomas Young (1773–1829) carried out the double-slit experiment: passing light through two narrow, closely spaced slits, he observed bright and dark fringes, a phenomenon explainable only by the interference of waves. Newton’s authority was such, however, that Young was ridiculed for years; only after the experimental and theoretical confirmation by Augustin Fresnel (1815) did wave theory prevail (Simonyi 2012, ch. 4).
Historical context — The return of the corpuscle
A twist of history: in 1905 Einstein showed that light also has a corpuscular nature (photons), partly vindicating Newton. Light is at once wave and particle: it is the wave–particle duality of quantum mechanics (Einstein and Infeld 1965, ch. 1). It is not a matter of choosing between two rival pictures, but of accepting that neither, on its own, suffices to describe the behaviour of light.
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Topics: Onde Concepts: Dualismo onda-particella · Interferenza
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