“Dear Radioactive Ladies and Gentlemen”

Wolfgang Pauli sent a letter to a group of nuclear physicists #OTD in 1930, proposing a new and hard-to-detect particle to explain energy that went missing in some beta decays. He dubbed them “neutrons” but we now call them “neutrinos.”

You can see a scan of Pauli’s neutrino letter (along with a translation) here:
http://microboone-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=953;filename=pauli%20letter1930.pdf

It was Edoardo Amaldi, in a conversation with Fermi, who coined the name “neutrino,” for “little neutral one.”

When Pauli realized how elusive his hypothetical particles must be, he said:

“I have done something very bad today by proposing a particle that cannot be detected; it is something no theorist should ever do.”

A few years ago I wrote about why Pauli proposed neutrinos, how they fit into Fermi’s theory of beta decay, and how they were eventually discovered in a beautiful experiment by Reines and Cowan. One of my favorite Twitter threads. https://twitter.com/mcnees/status/855180240351625216

Hopefully the thread gives an accessible explanation of a fact you often hear about neutrinos: They effortlessly pass through targets with lengths measured in light years.

Taking about neutrinos always brings to mind John Updike's poem "Cosmic Gall," from the December 17, 1960 issue of The New Yorker. It's true they have no charge, though now we know they have a (puzzlingly!) small mass. And they interact very weakly. But it's a lovely poem.