Question: What is the smallest subatomic particle found and recorded in the studies of quantum physics?

Gautam Kambhampati answered on 4 Mar 2019:

That’s a really interesting question!

Once you get down to really small scales it becomes difficult to say what the size of something is. Our best theory of particles (the Standard Model) tells us that the 17 most fundamental particles are single points, meaning they have no size. Some extensions of this theory, like String Theory, disagree and say that particles must have some size, because otherwise they would be like little black holes flying around.

We can also look at how heavy particles are. The photon, which is the particle of light, has no mass. There’s another particle, called the gluon, which also has no mass. The gluon is the particle that holds the nucleus of atoms together. The lightest particle that has some mass is called the neutrino, which is so light we can’t even measure how much it weighs! The neutrino is also really hard to detect, because it doesn’t interact with light. Because of this, some physicists think it is dark matter, which is the undetectable stuff that seems to make up 85% of the Universe.