Paul Dirac · Antimatter
If the equation gives two answers, what is the other one?
That time, that place
Until 1928 quantum mechanics and relativity ran apart. Schrödinger's equation fails when an electron moves near the speed of light.
Dirac was looking for an equation that joined them.
Why this question
The equation he found was beautiful. The electron's spin fell out of it on its own — a property that had until then been inserted by hand to fit experiment.
But it produced two sets of solutions. One was the electron we know. The other had negative energy.
Normally you discard such solutions as physically meaningless. Dirac did not.
What was found
He took those solutions to mean a particle with the electron's mass and the opposite charge. Nobody had ever seen such a thing.
In 1932 Anderson found it in cosmic rays: the positron. Four years after the prediction.
Hospital PET scans use it. Inject a substance that emits positrons; each meets an electron in the body and annihilates, giving off light whose position builds the image.
Trusting the equation and refusing to discard a solution became a machine that finds cancer.
Quantum mechanics could not handle fast electrons, and antimatter was not a concept
The positron detected in cosmic rays in 1932
Antimatter became real, and led to technologies such as PET imaging