In September 1933, Hungarian physicist and Jewish refugee Leo Szilard was struck by a world-altering idea while crossing a London street.

Irritated by Lord Rutherford’s dismissal of atomic power as ”moonshine,” Szilard envisioned a nuclear chain reaction: if an element could be found that emits two neutrons after absorbing one, it could sustain a liberated flow of energy.

This ”fantastic explanation” remained a theoretical puzzle for years, a ”bottled genie” of physics that Szilard feared could lead to devastating weapons if realized by Nazi Germany.

The critical breakthrough arrived in 1938, when Otto Hahn and Fritz Strassmann in Berlin unexpectedly split a uranium nucleus into barium—a process Lise Meitner and Otto Frisch later identified as ”fission”.

Meitner realized that the ”lost mass” from the split was converted into a colossal amount of energy, roughly 200 million electron volts per atom, according to Einstein's 𝐸=𝑚𝑐2.

When news of the discovery reached the global scientific community, physicists like Niels Bohr immediately grasped its significance.

For Szilard, the circle was complete: the mechanism for his chain reaction was real, and the race to control the terrible power of the unseen world had officially begun.