Wave theory had already won

Interference, diffraction, and Maxwell’s equations all made light a wave. Yet the photoelectric effect behaved oddly. Brighter light released more electrons but did not necessarily give each one more energy. Higher frequency did. Below a threshold frequency, even intense light failed.

Einstein proposed that light energy arrives in localized portions of size E=hνE=h\nu.

Photoelectric energy transfer Scientific model diagram metal metal Eγ = 4.5 eV Eγ = 4.5 eV Kₘₐₓ = Eγ − φ Kₘₐₓ = Eγ − φ 4.5 eV − 2.3 eV = 2.2 eV 4.5 eV − 2.3 eV = 2.2 eV Eγ > φ · ν₀ = 556.1 THz · electron emitted Eγ > φ · ν₀ = 556.1 THz · electron emitted − − Kₘₐₓ = 2.2 eV Kₘₐₓ = 2.2 eV vₘₐₓ = 879705 m/s vₘₐₓ = 879705 m/s incident window 3.408 μm incident window 3.408 μm escape window 10 nm escape window 10 nm separate spatial scales; physical time is real separate spatial scales; physical time is real
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Diagram description

Animated physics diagram: einstein_photoelectric_effect; showing time.

One packet, one electron

An electron spends the metal’s work function ϕ\phi to escape. The remainder becomes kinetic energy:

Kmax⁡=hν−ϕ.K_{\max}=h\nu-\phi.

Intensity changes how many packets arrive; frequency changes the energy of each.

Einstein did not erase the wave evidence. He exposed the failure of demanding that light fit one everyday category in every experiment. His Nobel Prize cited the photoelectric law, not relativity. The most famous relativist was honored for taking an awkward quantum idea more literally than its creator wanted.