Wave–particle duality

Wave-particle duality names the coexistence of localized detection events and wave-like interference in quantum mechanics. A photon or electron is detected as an individual event, yet the distribution of many events depends on probability amplitudes from alternative paths. If the alternatives remain coherent, adding the probability amplitudes before applying the Born rule gives an interference term; simply adding the separate path probabilities does not.

In the single-electron experiment of Akira Tonomura and collaborators, an electrostatic biprism divided and overlapped the electron wave, and a position-sensitive detector recorded individual arrivals. Successive accumulated records developed interference fringes. This makes the apparent tension concrete: localization describes the detector events, while matter-wave interference describes their statistical distribution.^[ref]

The history of light if funny.

First people thought it was a particle, as per corpuscular theory of light, notably Newton supported the corpuscular theory of light.

But then evidence of the diffraction of light start to become unbearably strong, culminating in the Arago spot.

And finally it was understood from Maxwell's equations that light is a form of electromagnetic radiation, as its speed was perfectly predicted by the theory.

But then evidence of particle nature started to surface once again with the photoelectric effect. Physicists must have been driven mad by all these changes.