What is the smallest subatomic particle?
The smallest particle that I am aware of is the quark. The quark is the basic building block of hadrons. There are two types of hadrons: baryons (three quarks) and mesons (one quark, one antiquark). Protons and the neutrons are stable baryons. There are also leptons, a family of elementary particles that include electrons, muons, tauons, and neutrinos. Neutrinos were originally believed to have zero mass, but they have been found to have a very tiny mass, smaller than any subatomic particle. Calling someone a ‘hadron head’ would be considered an insult among physicists.
What you probably have in mind is particles you can visualize, in which case a proton would be as good an answer as any. The electron, when acting as a particle, is the same size but 1837 times lighter; but the electron acts as a wave much of the time so it’s harder to visualize. Many of the other subatomic particles, such as quarks and gluons, can hardly be visualized even by nuclear physicists, but as long as the equations balance, the concepts are useful. The proton is 1/100,000th the diameter of an atom, and the atom is unimaginably small. Think of it this way: You have 50 trillion cells in your body. Of the needed elements in each cell, cobalt is present one hundred millionth as often as other elements, and only as part of the huge Vitamin B-12 molecule. And yet there are 450,000 atoms of cobalt in the average cell! The human body is like an onion. Every time you think you get to the bottom layer, there’s another layer to be investigated.
