The Pauli exclusion principle
Who
Wolfgang Pauli, an Austrian physicist whose father was born into a Prague Jewish family
When
1925
Where
Hamburg, Germany
Pauli's rule that no two electrons can occupy the same quantum state is why matter takes up space at all: without it, atoms would collapse and there would be no chemistry, no solids, no stars as we know them. He received the Nobel Prize for it in 1945.
Sources
Part of “The Gifts of the Jews” — verified Jewish contributions to the world, with sources.