### Video Transcript

What is the strangeness of a strange quark?

Another question could be: what’s the strangeness of this question? And our answer might be: it’s very strange. But let’s look into what these terms mean.

Let’s begin with this term called quark. What is a quark? To start getting an idea for what a quark is, let’s consider our standard model of the atom, which consists of three subatomic particles. Electrons which orbit the nucleus and protons and neutrons which make up the nucleus. Because we know about these three subatomic particles, we know that there is something smaller than an atom, namely, each of these three constituents. It turns out though that electrons, protons, and neutrons aren’t the only subatomic particles that exist. There in fact are many more. Quarks are one type of those additional subatomic particles.

One helpful way to think about quarks is in terms of their electric charge. When we think about fundamental electric charge, we may think about electrons and protons. An electron has a charge we can signify one e. And a proton has a charge opposite that but same in magnitude, negative one e.

The fact that both proton and electron have integer charge values in terms of the charge of an electron means that any net charge that is created by assembling some number of protons and some number of electrons will also have an integer charge value. And those are the charges we’re used to thinking in terms of, charges where the smallest unit is the charge of an electron or a proton. But, in fact, it’s possible to have a charge which is a fraction of this charge. And that’s how quarks are identified. In fact that’s a helpful way to define a quark, as a subatomic particle that carries a fractional electric charge. The charge of a single quark by itself then is not equal to the charge of an electron or a proton or some multiple of those values. It’s different; it’s a fraction of those charges.

If we go back to our question statement, we may come to understand though that this definition of quarks is incomplete. Because apparently there are different types of quarks and, in particular, something called a strange quark. And it’s true; our definition of quark doesn’t indicate that there are several different kinds or flavors of quarks. But, in fact, there are. According to current theory, there are six different types or flavors of quark: up, down, charm, strange, and top, bottom.

We see in this list of quark flavors that strange is one of the six flavors. And indeed it’s that kind of quark we’re being asked about in this question. So a strange quark is one of the six flavors of quark, where a quark is a subatomic particle that carries a fractional electric charge. So far, so good. But then, what about the strangeness of a strange quark or any other particle for that matter?

Strangeness, often abbreviated with a capital 𝑆, is actually a quantum number of a particle. So, in other words, it gives a fundamental property of that particle, like spin or magnetic quantum number. In particular, the strangeness of a particle describes the decay of the particle in certain interactions that occur over very short periods of time.

We’re familiar with radioactive decay, where an atom will change species into another type through a transformation. And strangeness talks about decay in certain interactions that occur over very short time scales.

In addition to that, there’s actually an equation for the strangeness of a subatomic particle. That equation is written this way. The strangeness of a subatomic particle is equal to negative the number of strange quarks in that particle minus the number of strange antiquarks in the particle. Note that quarks and antiquarks are one another’s opposites.

So, in our question, we’re being asked to evaluate the strangeness of a strange quark. In order to answer this question, we need to know two things. We need to know the number of strange quarks in a strange quark. And we need to know the number of strange antiquarks in a strange quark.

Well, let’s just think about this logically. How many strange quarks are in a strange quark? It’s not a trick question; the answer is one. And how many strange antiquarks are in a strange quark? Well, as we said, these two particles are opposites. So the number of strange antiquarks in a strange quark is zero. We find then that the strangeness of the strange quark can actually be written as a number. And it’s equal to negative the quantity one minus zero, or, simply, negative one. That’s the measure of the strangeness of a strange quark.