Physics
Albert Einstein
1879 – 1955 · Ulm, Germany
Space and time bend, and light sets the speed limit.
A light clock ticks each time a pulse bounces between two mirrors. Move the clock and the pulse has to travel a longer, slanted path, so the moving clock ticks slower by the factor γ.
01
The patent clerk
At sixteen he imagined chasing a beam of light and wondered what he would see. In 1902 he took a job checking inventions at the Swiss patent office in Bern, which left his evenings free to think.
02
1905, the miracle year
In one year he published four papers. Light arrives in lumps (quanta), which explains the photoelectric effect. The jiggling of pollen in water proves atoms are real. Space and time depend on how you move: special relativity. And mass is energy: E = mc².
The 1921 Nobel Prize was awarded for the photoelectric effect, not for relativity.
03
Gravity is curved spacetime
In 1907 he realised that a person falling freely feels no weight, and he later called it the happiest thought of his life. Eight years later, in November 1915, he finished general relativity: mass curves spacetime, and objects follow the curves.
A British eclipse expedition in 1919 measured starlight bending around the Sun by the predicted amount, and he became world famous overnight. GPS satellites must correct their clocks by about 38 microseconds a day for relativity, or positions drift by kilometres.
04
Exile and conscience
He left Germany when the Nazis took power in 1933 and settled at the Institute for Advanced Study in Princeton. In 1939 he signed a letter to President Roosevelt, drafted with Leo Szilard, warning that a uranium bomb was possible. He later campaigned against nuclear weapons.
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How they thought
Thought experiments
Ride a light beam, fall in an elevator: picture a simple scene so clearly that the physics has nowhere to hide.
Trust a principle over a habit
If the speed of light is the same for everyone, then time itself must give way, however strange that is.
Ask what is really measured
Time is what clocks read, so ask what two clocks actually show rather than what time should be.
Keep doubting, even your own field
He helped found quantum theory and then spent decades asking the hardest questions about it.
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Timeline
1879
Born in Ulm.
1902
Starts at the Swiss patent office in Bern.
1905
Light quanta, atoms, special relativity and E = mc².
1915
Completes general relativity.
1919
Eclipse measurements confirm that light bends around the Sun.
1933
Leaves Germany for Princeton.
2015
LIGO detects the gravitational waves he predicted in 1916.
“
In their own words
“Imagination is more important than knowledge.”
“I, at any rate, am convinced that He does not throw dice.”
I
Train your brain
Mastered 0 / 6
Where did Einstein work in 1905?
II
Train the machine
166 lines to learn, 38 held back. Names are removed. Random batches, dropout and noise make each seed take its own path.