Leó Szilárd (1898–1964) had his biggest idea while waiting for a traffic light. In September 1933, crossing Southampton Row in London, still annoyed that the great Rutherford had called atomic energy "moonshine", the light turned green — and as he stepped off the kerb it hit him: if a nucleus struck by one neutron released two, you'd get a chain reaction, and the energy of the atom would be very far from moonshine. Szilárd made a habit of being right about enormous things years before anyone else — his own motto for it: you don't have to be smarter than other people, just a day earlier.
Szilárd lived much of his life out of two suitcases, packed and ready by the door. It wasn't a quirk — it was calibration. He fled Hungary after the First World War, then read the political weather in Berlin and left Germany in 1933 on a nearly empty train, days before the border slammed shut behind refugees ("you didn't have to be much cleverer," he said, "just a day earlier"). In 1939 he drafted the letter — signed by his old friend and refrigerator-patent partner Albert Einstein — that warned President Roosevelt about atomic bombs and set the Manhattan Project in motion. Then, in 1945, he did something rarer than starting the project: he fought to stop the bomb being dropped on cities, organising the Szilárd petition signed by dozens of the scientists who had built it. He spent the rest of his life campaigning for arms control.
In 1929 — decades before "information theory" existed — Szilárd imagined a box containing a
single molecule. A tiny demon peeks to see which half the molecule is in, slides
in a partition, and lets the molecule push it back out, extracting work from pure knowledge. Run
it forever and you'd break the second law of thermodynamics… unless knowing itself has a
thermodynamic price. Szilárd pinned that price at exactly
Szilárd treated entire disciplines the way other people treat hobbies. With Einstein he patented a refrigerator with no moving parts (motivation: a Berlin family killed by a leaking fridge seal; the pumping was done by electromagnetism — a descendant design later cooled nuclear reactors). After the war, appalled by what physics had wrought, he switched to biology: he co-invented the chemostat, a device that grows bacteria at a steady, controllable rate and became a workhorse of microbiology, did early work on how cells regulate themselves, and helped found the Salk Institute. He published fiction too — his story collection The Voice of the Dolphins imagined dolphins brokering world peace, since the humans clearly weren't managing. A day earlier than everyone, in every field he touched.