What is the weak nuclear force and why is it important?

Back in the 1930s, physicists were doing experiments involving what they called "beta decay." They observed that an element would suddenly spit out a fast-moving electron, and once it was done, it would be different — sometimes a different isotope of the same element, and sometimes a different element altogether.

So the question on everybody's mind was, exactly how did this decay process unfold?

Enrico Fermi had an answer: a new force of nature. We knew that the nucleus of an atom was a bundle of neutrons and protons. Fermi hypothesized that some new force could change a proton into a neutron, or vice versa, and, in the process, release an electron and a nearly massless particle called a neutrino.

It was just a guess. But he was right, and the weak nuclear force was born.

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