Twenty-one grams.
That is the mass of all of the electrons in your body if, like me, you weigh about 70
kilograms.
Now all of the mass comes from the Higgs mechanism, which means that as your electrons are traveling
through space time, they interact with the Higgs field and it is that that gives them
their mass.
It slows them down and stops them from traveling at the speed of light.
But most of your mass doesn’t come from the Higgs mechanism.
And neither does all of this stuff that you see around you.
The mass is coming from somewhere quite different and that is because most of your mass and
most of this mass comes from neutrons and protons and they are not fundamental particles.
They are made of constituent particles called quarks.
Now the theory that describes quarks and their interactions with each other through gluons
is called quantum chromo dynamics.
And chromo is the Greek word for color.
So in some way these objects are meant to carry the color charge.
But they are much, much smaller than the wavelength of visible light, so there is no way that
they are actually colored, but it is a useful analogy that helps us think about how they
interact and the particles that they can make up.
Now the rules are pretty simple.
In order for a particle to exist, it must be colorless or white, like this house.
Now you can accomplish that in two different ways.
You could make three quarks in where each one is a different color, red, green and blue,
so overall they combine to produce white.
Or you could use a quark and an anti quark where one is a color like green and the other
is its anti color, say, magenta.
Now what I would like to do on this little patch of beach behind me is simulate how quarks
actually bind together and form different particles.
Now for this you need to remember that in the last video we talked about how empty space
is not truly empty.
So the beach here is has these undulations in it which represent the fluctuations in
the gluon field.
But you have to imagine this beach sort of rippling and these bumps coming and going.
Now that is really important, because to get rid of those fluctuations actually takes energy.
And this is an important part of binding the quarks together.
The existence of quarks actually suppresses the gluon fluctuations and creates what is
called a flux tube, an area where there is really nothing in the vacuum and that is in
between this quark and the anti quark.
And that pairs them up and creates what is called a meson, the quark, anti quark pair.
What is interesting about that flux tube is that as these quarks become more separated,
the flux tube remains the same diameter and the same sort of depth of suppression of the
field, which means that the force doesn't actually increase.
It is not like a spring.
It is not like an elastic band.
The force is the same that is pulling these quarks back together.
But you are putting more work in as you move these quarks and anti quarks further apart.
And so for a time people thought: Well, these quarks are always going t be confined, however
far you move them.
You are just going to get a really long flux tube.
But what actually happens is you that you put in enough energy that you can actually
create a quark, anti quark pair.
>> Nevertheless, the quarks are still combined.
You can never see an individual quark, because if you try to pull it out, you put so much
energy into the situation that another quark, anti quark pair will be created.
>> Now to form a proton, we are going to need an up quark, another up quark and a down quark.
Now the standard model of a proton that you have probably seen involves these quarks bounded
together by little gluon springs that go between them.
>> We know that that picture is totally wrong now.
Even in the best sense you might have hoped that you would see flux tubes around the edge
of the triangle.
But we know that, in fact, they don’t do that.
That you get these y shaped flex tubes.
>> The crazy thing about a proton is that there may be more than three quarks there.
You see, you can have additional quark, anti quark pairs pop in and out of existence.
So at any given time there could be five or seven or nine, any odd number of quarks could
make up a proton.
So this is what a proton actually looks like.
You can see that the quarks like to sit on those lumps in the gluon field.
And you can see the two up quarks and a down quark, but there is also a strange quark and
an anti strange quark, which is strange, because you don’t normally think of these quarks
being inside a proton, but they can be at any particular point in time.
And you can also see that these quarks have cleared out the vacuum.
And you can see that there is kind of these flux tubes which are the areas where the gluon
field has been suppressed.
And that is really what is binding these quarks together.
>> That is the strong force that binds quarks into the heart of the proton.
>> It is intrinsically related to the fact that clearing out those fluctuations has more
energy than where they are.
>> That is right.
It costs energy to clear the vacuum.
>> So where is the mass of the proton really coming from?
Well, of course, the constituent quarks do interact with the Higgs field and that gives
them a small amount of mass.
But if you add up the mass of all the quarks in the proton it would only account for about
one percent of its total mass.
So where is the rest of the mass coming from?
The answer is: energy.
You know, Einstein’s famous equation: E equals mc squared.
Well, that says we have got a lot of energy for just a little bit of a mass.
But if you rearrange the equation you can see that we can get an amount of mass if there
is lots of energy there.
And that is really where most of the mass of the proton is coming from.
It is from the fact that there are these energy fluctuations in the gluon field and the quarks
are interacting with those gluons.
That is where your mass is coming from.
It is coming from the energy that is in there.
You know, Einstein talked about, well, if I had a hot cup of tea, it would actually
have a slightly greater mass than the same cup of tea when cold.
And he was right.
I mean, you can’t measure it with a cup of tea, but most of your mass you owe to E
equals mc squared, you owe to the fact that your mass is packed with energy, because of
the interactions between the quarks and these gluon fluctuations in that gluon field.
I think it is extraordinary, because what we think of as ordinarily empty space, you
know, that turns out to be the thing that gives us all most of our mass.
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