Quarks

A diagram of a proton, made from two up quarks and one down quark. They all mediate gluons, which are bosons that control the strong nuclear force.

What Are Quarks?

Quarks are very small, fundamental, elementary particles that make a large portion of the standard model, and are the building blocks for atoms. There are six types of quarks, or flavours of quarks. Quarks are “Fermions,” meaning that they follow the Fermi-Dirac statistic. This is a fancy way of saying that all elementary particles (Quarks, Leptons and Bosons) are split into two groups: Fermions, which are Quarks and Leptons, and Bosons, which are force mediating particles.

History

Quarks were first theorised in the 1960’s by two physicists, at the same time, by Murray Gell-Man and George Zweig. In the 60’s, before quarks, everyone thought the smallest particles were protons and neutrons, however people were realising equations weren’t matching up and that protons and neutrons mustn’t be elementary particles, they must be made from something. They were originally going to be called Aces, however this was passed and instead, thought to name them “quacks…” after ducks. Bizarre choice. However, Gell-Mann was reading work by James Joyce, an Irish poet, and he read a line which read “Three quarks for Muster Mark!” Which is were the name originated from.

The theory was proposed but no evidence was seen. And so began extensive testing, looking for evidence of quarks. The thing about quarks is that the protons and neutrons are held together by the strong nuclear force, and the further you try to break them apart, the more they want to stick together, so attempting to break protons to reveal the quarks, proved futile. However, the great Richard Feynman looked into this and made quite a discovery. He proposed to observe the proton, as an electron, through General Relativity. Imagine you are an electron, hurtling towards the proton/neutron. If you are an electron, and you’re moving near light speed, you view the wavelength of everything, to be contracted, to be squashed, so everything looks flat and two dimensional. And so you’ve got three flat blobs which are the quarks of the proton/neutron. And you can measure that the electron, instead of bumping into a circle that’s the proton, you can measure the electron hitting one of the three quarks, which form a triangular shape, and diffracting off. And so this provided evidence of these individual particles existing in the proton.

Quark Pairs

There are six known quarks, divided into three generations. Quarks can only really exist in groups, unless they’re in extreme conditions, like extreme temperatures or gravity. But usually they exist in groups, which create matter known as “Hadrons”. Hadrons are particles that are composed of quarks, which are then split further into two families: Baryons and Mesons. Three quarks that come together are called “Baryons.” Baryons are particles like Protons and Neutrons that create the nucleus of atoms. Quarks can exist in pairs, they are two quarks, bound by the strong nuclear force called quark-antiquark pairs, which are more commonly known as “Mesons.”

Particles comprised of more than three quarks are known to exist, pentaquarks are known, these are Hadrons made from five quarks. However, not a lot is known about them, and they are incredibly unstable. They don’t naturally exist throughout the universe, however it is possible that they could exist in places like Neutron Stars, stars which are very mysterious, and are very dense.

Antiquarks

For every quark, there is an antiquark to match. Antiquarks are identical to quarks, except from one thing. The charge symbols for the charge of the quark is opposite. So if the charge for a quark is -1/3, then the charge on the antiquark, is +1/3.

Generations

The six quarks are divided into three generations. This is because each pair in the generation above, have greater mass and energy levels than the previous generation. This hierarchy of mass and energy is what causes the generational decay of the quarks, explaining why the first generation of quarks are greatly more abundant that the next two, because the next two generations gradually decay to the previous generation. Meaning large generation three quarks (which some are twice the size of protons) will decay into generation two quarks, and generation two quarks will decay into generation one quarks.

The Quark Family – Generation I

The first generation of quark pairs are: the “Up Quark” and the “Down Quark.” The up quark has a charge of +2/3, and the down quark has a charge of -1/3. This is the first generation and they make up protons and neutrons. The combination of two up quarks and one down quark, creates a proton, and you can calculate this, simply by taking the sum of the charges. So we know the charge of a proton is +1, so: (+2/3) + (+2/3) + (-1/3) = 1. And so a neutron is made from two down quarks, and one up quark. So the charge of a neutron is 0. So: (-1/3) + (-1/3) + (+2/3) = 0.

The Quark Family – Generation II

The second generation of quark pairs are: the “Charm Quark” and the “Strange Quark.” The charm quark is an up type quark, and the strange quark is a down type quark. These quarks are heavier than the previous quarks, and have a lot more energy.

The Quark Family – Generation III

The third and final generation of quarks, are: the “Top Quark” and the “Bottom Quark.” The top quark is the up type quark and the bottom quark is the down type quark. These quarks have the most mass and energy out of the rest of the quarks.

Properties

Quarks have many interesting properties to them. Quarks have mass, they have electrical charge, they have a colour charge and they have a spin. They are also the only elementary particle in the standard model that interacts with all four fundamental forces: gravity, electromagnetism, the weak nuclear force and the strong nuclear force.

Questions

Nowadays, quarks are still quite mysterious. We know of the basic quarks like the up and down, however the top and bottom were only discovered in 1995, which is very recent. So there definitely could be more particles still to discover, perhaps dark matter has its own exotic quark types? And when it comes to neutron stars, there’s theorised quark seas, or quark plasma in them, due to the extreme temperatures, gravity and density. And we still don’t really know anything about what that is.

So this pretty much wraps everything up! I hope you learned something knew from this, and if you have any theories or want to mention more on this, feel free to comment below. Thank you for reading this!