When you're a kid, you're told that all the stuff around
is made of atoms and that atoms are made of protons
and neutrons and electrons.
And if you're lucky, you're told what protons and neutrons
are made of.
They're made of three quarks each.
But if they're both made of quarks, how are protons
and neutrons different?
You're not usually told this as a kid.
And you're not usually told what quarks are
and why they're called quarks when they're clearly
spelled quarks.
So protons are made out of three quarks.
That's the first lie you're told.
Protons are not that simple.
At any given time, the proton will have two
up quarks with charge plus 2/3, and a down quark with charge
minus 1/3, which of course all add up to positive 1,
because that's the charge of the proton.
These three quarks are known as valence quarks
and they're definitely there.
But the proton could have an additional
up quark, anti-up quark pair.
An anti-quark is the anti-particle of a quark.
And it could have other types of quarks-- pairs
of strange quarks and anti-strange quarks, charm
quarks, and anti-charm quarks.
In fact, the proton likely has tons
of quark, anti-quark pairs.
But there is more.
The quarks are held together by the strong force,
which is carried by particles called gluons.
So inside the proton, there are zillions of gluons and quarks
all zooming around close to the speed of light
and colliding and annihilating and new ones are forming
and it's a crazy, raging party.
Such is the quantum world in a proton.
Wouldn't that violate some kind of conservation law
if particles just appeared in the proton?
Quarks can and do just appear and disappear,
but not out of nothing.
Einstein's famous equation, e equals mc squared
means that mass can turn into a lot of energy
or a lot of energy can turn into mass.
In fact, the quarks that comprise a proton only
make of 1% of the total mass of that proton.
That's like saying I drop some quarters in a bag,
and suddenly it weighs 10 pounds.
There's a lot of energy in all the motion
of those crazy, partying particles-- party-cles.
And there's energy in the gluon field.
All of this energy contributes to the mass of the proton, e
equals mc squared.
All we need to conserve is the total mass energy
of the proton and nothing is violated,
as quark, anti-quark pairs pop in and out of existence.
But there are a few other constraints.
The total number of up quarks must
be two more than the anti-up quarks
and there must be one more down quark than anti-down quarks
so that the valence quarks come to a total of three
and the quark, anti-quark pairs of other types
must all cancel out, like the top quark and the charm quark
and the strange quark and the bottom quark.
When quark pairs spontaneously appear in the proton,
other properties must be conserved as well, like charge.
So if a quark with charge positive 2/3 appears,
its partner must have charge negative 2/3.
And the spin of the particles must be opposite,
and the colorless of the proton must be conserved.
This is cool.
Quarks all have color, except it's not like real color.
Color in quarks is a type of charge,
like the electric charge, except instead
of the electromagnetic force, it corresponds
to the strong force.
Quarks can be red, green, and blue, like the three
primary colors of light.
And when you mix those colors, you get white light.
So when I said that protons are colorless,
that means that their three valence quarks
must be red, blue, and green.
So clever.
The quarks can change color, but the overall color
has to stay white.
It turns out that the anti-quark has the opposite color,
so that would be like anti-red, which cancels out red.
But I think the most amazing thing about quarks
is that we know all of this about them
without ever directly detecting one.
In fact, you can never detect just one,
because they're never found alone.
The more you separate the quarks, the more energy
you have to put in to pull the quarks apart.
And as you do so, you eventually put in enough energy
to make up the mass of two new quarks that could then
bind to the original two.
So next time you're told there are three quarks in a proton?
There are three valence quarks, and a sea of other
quarks-- too many to count, impossible to count.
No, really.
We can't take a snapshot.
Now, if you want to find out more about quarks,
check on my blog post here on Ten Quirky Facts About Quarks.
And if you want to find out how big a quark is
and how we image tiny things, like protons and quarks,
check out my video on the smallest
things in the universe.
Thanks for watching.