There are so many fascinating facts about these fundamental particle of matter – too many to fit in this short and sweet (pun intended) video on quarks. So I wrote up some of my other favorite facts here. Enjoy!
1. Quarks come in flavors
There are six types or flavors of quarks - up, down, top, bottom, charm and strange. The particles that make up most matter we interact with - protons and neutrons - are both made of up and down quarks. The other four quarks are rarely detected because they decay so quickly, some only living as little as 5 x 10^-24 seconds. Because of this, the top quark was not discovered until 1995, though it was theorized in 1973.
2. Quarks may have no size
Quarks are the smallest particles that we know of. We’ve measured them down to 10^-19 meters and have seen no indication of sub-structure. Quarks, along with leptons (e.g. electrons and neutrinos) are what we call elementary particles because, as far as we’ve measured, they are not comprised of any smaller particles. They may in fact have no size, though this would cause problems for the math we use to describe them.
3. Quarks were discovered in a similar way to the atomic nucleus
Quarks were discovered in particle collisions in 1967 at the Stanford Linear Accelerator Center. When electrons collided with protons, they rebounded having hit something seemingly harder than the “soft core” the protons were thought to have. This indicated there was something smaller, a substructure to the proton.
4. Quarks are pronounced "kworks"
Though some still pronounce quarks as they are spelled, quarks are properly pronounced "kworks." They were theorized by Physicist Murray Gell-Mann, named them quarks, called them "kworks," and got the name from line of a James Joyce poem:
Three quarks for Muster Mark!
Sure he hasn't got much of a bark
And sure any he has it's all beside the mark.
5. Quarks were one of the first particles to form in the universe
Starting around 0.000000000001 (10^-12) seconds after the big bang, the universe cool down to a balmy 10 quadrillion degrees. During this time, the quark epoch started, and large numbers of quarks formed throughout the universe. It wasn't until 0.000001 (10^-6) second later that the universe cooled enough for quarks to bind and form protons and neutrons.
6. Quarks are never found alone
When you try to pull two quarks apart, you have to put so much energy in that before you overcome the strong force holding them together, you will put enough energy to create two new quarks that bind to the original two. We call this state of perpetual togetherness "quark confinement."
7. Quarks Have Color
Quarks have color charge. The electromagnetic force, responsible for light, electricity, and magnetic pull, has a charge associated with it - the electric charge. But the strong force also has a charge associated with it, and we call it color charge. It comes in three colors: red, green and blue. But quarks are not actually colored - they are too small to reflect visible light. In order to have color as we normally think of it, quarks would have to be over a trillion times larger.
8. Quarks Can Change Color
Quarks inside of a proton can change color by exchanging gluons, the virtual particles that carry the strong force and hold quarks together. But the overall color of the proton must remain white, so the three valence quarks in a proton must always be red, green and blue. So when one quark changes color, another must change as well.
9. Antiquarks Have Anticolor
Quarks have an associated anti-particle called an antiquark. When quark/antiquark pairs appear in a vacuum, they must have opposite spin, opposite charge, and opposite color. So antiquarks can have the color charges antered, antigreen, and anti blue. When these quarks/antiquark pairs collide, they annihilate.
10. The strong force holds quarks together
The force that holds quarks together inside of a proton or a neutron is called the strong force. It's carried back and forth between the quarks by particles called gluons, just like the electromagnetic force is carried by photons.
For more information about quarks, check out this fantastic website, the Particle Adventure, created by the Berkeley Lab.