Question: What is a neutrino?

Jordan McElwee answered on 17 Mar 2020:

It’s the smallest particle that we know of! The next smallest particle is the electron (which is already pretty tiny), and the neutrino is at least 250,000 smaller than that. They come in 3 flavours (types) called the electron, muon, and tau neutrino which are paired with (surprise!) the electron, muon and tau. They were first proposed by Wolfgang Pauli in 1930 to explain why (apparently) energy wasn’t conserved in beta decay, and then first detected in 1956.
They also undergo a process called ‘Oscillation’, in which different types turn into one another. This is as weird as throwing an apple into the air and catching it as an orange! As far as we know no other particle does this.
They are certainly an interesting particle, and there’s a lot of people investigating them!