The surprising origins of wave-particle duality

Wave-particle duality is a fundamental concept in quantum physics that describes how quanta, such as photons and electrons, exhibit both wave-like and particle-like properties. This duality was first observed in light experiments in the early 20th century but has roots stretching back to debates over the nature of light between Christiaan Huygens, who proposed a wave theory, and Isaac Newton, who favored a particle description. Huygens’ wave theory explained phenomena like interference and diffraction but couldn’t account for polarization, while Newton’s corpuscular theory described light’s color spectrum but failed to explain interference patterns.

The double slit experiment by Thomas Young provided strong evidence for light’s wave nature through observable interference patterns. Later, Augustin-Jean Fresnel’s wave theory of light was experimentally validated by François Arago, who demonstrated the presence of a bright spot in the shadow of a sphere, a prediction considered absurd by Newtonian adherents like Simeon Poisson. James Clerk Maxwell’s equations further solidified light as an electromagnetic wave.

Albert Einstein’s work on the photoelectric effect revealed that light’s energy is quantized, suggesting a particle nature. Modern experiments with the double slit further confirm wave-particle duality, showing that quanta behave as waves when unmeasured but as particles when observed. This duality remains a cornerstone of quantum mechanics, with experiments consistently supporting the non-deterministic nature of quantum phenomena, defying attempts to reconcile it into a single deterministic framework.
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