photons

Glass is transparent because visible photons lack the energy to excite its electrons and its uniform, grain-free structure scatters almost nothing sideways.

In 1923, Arthur Compton showed that X-rays scatter off electrons like billiard balls — shifting wavelength in a way only particles explain. The Compton effect settled the wave-particle debate and won the 1927 Nobel Prize.

Hertz spotted it in 1887. Lenard mapped its rules. Einstein explained it in 1905. Millikan spent a decade trying to disprove Einstein — and ended up confirming him.

Light is both wave and particle. Explore photons, the electromagnetic spectrum, polarization, lasers, and quantum entanglement explained simply.

Planck proposed energy is quantized in discrete packets (quanta). This radical idea solved the blackbody paradox and launched quantum mechanics.