In 1933, on the corner of Southampton Row and High Holborn in London, Leo Szilard had an epiphany: while crossing the street, he had the idea for a nuclear chain reaction. This idea would be instrumental in building the atomic bomb during WWII.

The exact point where Szilard crossed the street remains unknown, but this picture displays the vicinity of the place where he paused for the traffic light. Please note that the picture was taken about 50 years after Szilard’s idea of a nuclear chain reaction.

(MSS 32, Box 100, Folder 6)

"As I was waiting for the light to change and as the light changed to green and I crossed the street, it suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbed one neutron, such an element if assembled in sufficiently large mass, could sustain a nuclear chain reaction. I didn’t see at the moment just how one would go about finding such an element or what experiments would be needed, but the idea never left me."

-Szilard recalling how he had this idea and what it meant, keeping it a secret by patenting it

Photo of Szilard in the hospital bed recalling his epiphany

(MSS 32, Box 100, folder 7)