Dear Dean,
There’s a pencil lying on my desk right now. It’s not much to look at, but what if I could zoom way in and see the protons and other itty-bitty stuff inside it?
My friend Ryan Corbin told me it would be like looking at a bubbling soup of fundamental particles. He’s a quantum physicist at Washington State University.
He told me that protons—along with neutrons—form the nucleus in the middle of an atom.
“Atoms make up all the stuff that we see,” Corbin said. “An atom has neutrons and protons in its nucleus. Protons have a positive electric charge. Neutrons have no electric charge. And then around the nucleus—very far out—there are electrons with negative electric charge.”
An atom is the smallest bit of an element that’s still that element. The graphite inside my pencil is the element carbon. An atom of carbon would be the teeniest bit of carbon possible. An atom of carbon is so tiny that you can’t even see it using a regular microscope.
But if you could zoom in on a basic carbon atom, you’d see six protons and six neutrons clumped together in the middle. You’d see six electrons, too.
Sometimes people say electrons orbit the nucleus. Corbin told me it’s not really like how the planets orbit the sun. It’s more like a smear-y cloud of possible places the electrons could be. You can’t poke a wee finger at an electron and say, “There it is!”
Electrons are fundamental particles. As far as we know, they’re not made of anything smaller.
Protons (and neutrons) are made of a different kind of fundamental particle. They’re quarks. Every proton has three main quarks—called valence quarks. They can be up quarks or down quarks.
Quarks are the reason protons have a positive charge. Each quark has a fraction of an electric charge. A proton has two up quarks and a down quark. Up quarks have a +2/3 charge, and down quarks have a -1/3 charge. If you add and subtract those fractions, you get the +1 charge of a proton.
Valence quarks get lots of attention. But they’re about 1% of what’s inside a proton. Protons also contain another kind of fundamental particle that acts like glue between quarks. It’s called a gluon.
The quarks trade gluons back and forth. Protons trade gluons with neutrons and other protons. All that trading makes the strong force. That’s what holds together an atom’s nucleus. It’s why protons stick together—even though things with the same charge repel each other.
“Those quarks and gluons only get you part of the picture,” Corbin said. “There’s also this bubbling sea of quark and anti-quark pairs that can pop in and out of existence. We call them sea quarks because there’s this sea of bubbling, frothy quantum weirdness happening.”
In addition to the three valence quarks, tons of other quarks blip in and out of reality inside a proton—like the bubbles forming and popping in a boiling soup.
That can happen because there’s lots of energy inside the proton. Energy can change into mass and back into energy again. That’s one of the things Einstein figured out.
All that happens inside everything—even my boring pencil or the atoms that make me. I guess you could say the universe is a weird and quark-y place.
Sincerely,
Dr. Universe