Chien-Shiung Wu
Does nature tell left from right?
That time, that place
Physics took one thing entirely for granted: nature does not distinguish left from right.
Hold any process up to a mirror and the laws should hold just as well in the mirrored world. This was called parity conservation, and no one doubted it.
Why this question
Then Lee and Yang made an awkward observation: the principle had actually been tested only for the strong and electromagnetic interactions. For the weak interaction, no one had ever checked.
Everyone assumed it, so no one measured it. The experiment was difficult and the outcome looked obvious.
What was found
Chien-Shiung Wu measured it.
She cooled radioactive cobalt to near absolute zero and used a strong magnetic field to align the nuclei in one direction. Then she counted which way the electrons flew as those nuclei decayed.
If left and right are equivalent, both directions should be equal.
One direction was clearly favored. In the weak interaction, nature does tell left from right.
Before the result came in, Pauli had bet that God could not be left-handed. He lost.
Nature does not distinguish left from right
Electrons emerging preferentially in one direction from aligned nuclei
The next year's Nobel went to Lee and Yang, who had made the proposal. Wu, who performed the experiment, was left out