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Why did Einstein win the Nobel Prize?
The short answer (tap to open)
Albert Einstein won the 1921 Nobel Prize in Physics for explaining the photoelectric effect, the idea that light comes in packets, not for relativity. Relativity was still controversial with the committee. His packets of light, later called photons, became one of the foundations of quantum physics.
How did light in packets win the prize?
Card 1 · 1905, Bern
Einstein is 26 and works as a clerk at the Swiss patent office. In one year he publishes four papers that change physics. One of them, in March, says light comes in small packets of energy.
Card 2 · The puzzle
Shine light on certain metals and electrons fly off. Brighter light knocks out more electrons, but not faster ones. Only the colour changes their speed, and below a certain colour nothing happens at all, however bright. Wave theory can't explain it.
Card 3 · Einstein's answer
Light arrives in packets, and each packet's energy depends on its colour. One packet knocks out one electron. A dim blue packet can do what no amount of red can. This is the photoelectric effect, and it's how your camera sensor works today (the introduction).
Card 4 · Nobody believes him
For years most physicists reject the packets. Light is a wave; Thomas Young proved it a century earlier (chapter 4). Robert Millikan spends a decade testing Einstein's formula, expecting to disprove it. By 1916 his measurements confirm it exactly, though even then he doubts the packets themselves.
Card 5 · 1922, Stockholm
The Nobel committee has struggled with Einstein for years. Relativity is famous but still disputed, and one influential committee member objects to it. So in 1922 the committee awards him the prize it held back from 1921, "especially for his discovery of the law of the photoelectric effect". Einstein is on his way to Japan when the news arrives.
Card 6 · A twist
Einstein gives his Nobel lecture the next year, in Gothenburg. He talks about relativity anyway. The prize money goes to his first wife, Mileva Marić, as agreed in their divorce.
Card 7 · The irony
The packets Einstein introduced became photons, a pillar of quantum physics. Yet he spent the rest of his life arguing that quantum theory was incomplete, which led to the entanglement debate in chapter 5.
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