How Many Elementary Particles Are There, Really?

So Natalie, what's the big idea?

The big idea here is that when you start trying to count the fundamental particles, which seems like it would be an easy thing to do given that we've discovered all of these particles in experiments at the Large Hadron Collider and previous colliders, we have a theory that beautifully describes all these particles, so it seems like you'd be able to just say how many there are.

But in fact, this question kind of opens up a Pandora's box.

There are just many layers of complexity here.

Yeah.

Like your column, I'd like to go from the simple, and this is relatively speaking simple, to the complex.

Tell me what the Standard Model is so that we can get to a baseline to start counting.

The Standard Model is a quantum field theory, and it's the quantum field theory that describes all the fields and their associated particles that we know of in the universe, and the relationships between them.

You can think of the Standard Model as a set of equations or even one master equation that describes all the pieces and how they fit together.

They actually account for all the matter we know of and all three of the quantum forces.

So the only force that isn't included is gravity, which is described in a different way.

Okay, so I have an understanding of quantum field theory sort of in the abstract, which is to say we have a set of observations.

They involve the results of experiments that show quantum effects, that we get the results from particle colliders.

That gives us more information, and it all fits beautifully into a mathematical framework that allows us to make predictions that turn out to be true 'cause the Standard Model's quite well-established, right?

Mm-hmm.

What I don't have is a clear, intuitive sense of what we mean when we describe a quantum field.

Yeah, it is strange.

When I picture it in my mind, I really think of the surface of a pond or maybe like the surface of a trampoline.

It fills all of space, so it's not two-dimensional in that way.

But you can think of it as an entity that has a zero point where it's fully relaxed, and then any fluctuations in the field, so any little ripples in that surface, are particles.

So fluctuations, vibrations in this otherwise still entity is what I think of as a quantum field.

These fields are extending through space.

There's a lot of them, and they're all overlapping each other.

So when one fluctuates, it actually affects another field, and they're all related.

We can think of that as fields spilling into each other or vibrations in one setting off vibrations in another, or you can think of it as the particles that are those vibrations colliding or interacting or one morphing into another.