Hello there, physics fans.
This is our eighth episode.
This whole time, I have been sitting in this chair, which has resulted in an …ahem…an
increase in my mass.
That works out just perfectly for today’s subject, which is the origin of mass of fundamental
subatomic particles, also known as the Higgs field or, somewhat incorrectly, the Higgs
boson.
And >>that<< is what I’m going to talk about in today’s episode of Subatomic Stories.
So far in this video series, we’ve talked about the ultimate building blocks of the
universe and the rules that govern them.
We’ve talked about the quarks, the leptons, and the particles that transmit the subatomic
forces.
Taken together, these objects make up most of the Standard Model of particle physics,
which is a big piece of creating a theory of everything.
There’s just one piece of the Standard Model we haven’t covered and that’s called the
Higgs field.
So just what is the Higgs field and why did the Standard Model need it?
Let’s answer the second question first.
In the 1960s, a bunch of theoretical physicists were looking into connections between the
weak nuclear force and electromagnetism.
We talked about these forces in an earlier episode.
At first inspection, these two forces seem very different, with different strengths,
ranges, and behaviors.
However, after a lot of work, it became clear that the two forces were different manifestations
of the same thing, kind of like how liquid water and ice can both be explained by the
molecular nature of water.
The underlying force from which electromagnetism and the weak force arise is called the electroweak
force.
There’s only one problem.
Electroweak theory only works if the weak and electromagnetic force carrying particles
are massless and, of course, they’re not.
The electromagnetic photons are massless, but the W and Z bosons of the weak force are
actually very massive.
So that could have killed the whole electroweak idea.
However, in 1964 several groups of physicists published some ideas that solved the problem.
They postulated that there was an energy field that permeates the entire universe that we
now call the Higgs field.
Some particles interact with that field and get mass, and others don’t.
Higgs theory was originally designed to explain the mass of the heavy force carrying particles,
but it was later shown that the same field >>ALSO<< explained the masses of the quarks
and the charged leptons.
The jury is still out on the relationship between the Higgs field and the neutrinos.
If you want to understand the history of the development of the Higgs field, I strongly
recommend a book called “Massive” by Ian Sample.
It tells the rich and complex story.
Now I don’t want to describe analogies here on exactly how particles are given mass.
Two of my very best longer videos do just that.
One is on the Fermilab channel and one is with TED-Ed.
If you want the analogies, look to the links in the description below.
Here, what I want to do is just state a couple of key points.
It is often said that the Higgs field interacts with massive particles, but that’s exactly
backward.
Many objects have what is effectively a Higgs charge.
Those that do have the Higgs charge interact with the Higgs field and gain mass.
Those that don’t are massless.
That’s an important point.
The interaction is the cause and the mass is the effect, not the other way around.
If the Higgs field exists, then there should also exist vibrations of the Higgs field.
Vibrations of subatomic fields is just a fancy way to say “particles.”
For instance, the quarks are vibrations of the quark fields and leptons are vibrations
of lepton fields.
The vibration of the Higgs field is called the Higgs boson.
The discovery of the Higgs boson was made on July 4, 2012.
It was discovered by…well…me.
OK, OK, this time it was me and six THOUSAND of my closest personal friends using data
recorded at the CERN LHC.
But, just like the top quark saga I mentioned in episode 2, my mom somehow got the wrong
idea and…well you know.
Shhhh.
Don’t tell her.
It would break her heart.
The announcement was a huge deal, culminating nearly half a century of scientific inquiry.
Physicists Francois Englert and Peter Higgs shared the 2013 Nobel Prize in physics for
their predictions back in 1964.
Great fanfare.
Great accolades.
We all should be suitably impressed, right?
Well, actually, we should.
It was a big deal.
But there are some untold stories.
First, there is a dark secret of the theory of the Higgs field.
While the field gave mass to fundamental subatomic particles, Higgs theory doesn’t arise from
any deep physical principle.
It was added to make the Standard Model work.
Intellectually, it’s just a Band-Aid.
We’re still waiting for a way to motivate the Higgs field from first principles.
Second, it’s often said that the Higgs field is the origin of mass, but it’s much more
accurate to say that the Higgs field is the origin of mass for fundamental subatomic particles,
like the quarks, the leptons, and some force carrying particles.
When you ask how much it contributes to >>YOUR<< mass or the matter made of atoms, it’s only
two percent.
I don’t have time to explain that here, but I made an awesome longer video about that
surprising truth and the link is in the description.
If you’re wanting a sneak peek into the origins of mass, well it’s Einstein’s
fault.
Somehow it’s always Einstein.
Furthermore, the matter of atoms only makes up five percent of the mass and energy of
the universe.
The rest is dark matter and dark energy.
We’ll cover those in upcoming episodes.
If you put those two ideas together, the Higgs field is only responsible for zero point one
percent of the mass of the universe.
So, what’s the big deal?
Zero point one percent is nothing, right?
Except if the Higgs field didn’t exist, electrons wouldn’t have mass and, therefore
atoms wouldn’t exist and, therefore, neither would we.
So – yeah – the Higgs field really >>IS<< a big deal.
OK, so that’s all the time we have today.
Let’s take a look at viewer’s questions.
Hi guys, it’s that time of the episode where I answer viewer’s questions.
Our first question is from an earlier episode, but I didn’t have time to answer it, so
here goes.
Jan Pieter Cornet asks if neutrons decay via the weak force, why is any element other than
hydrogen stable?
That’s a quite sensible question.
Neutrons are heavier than protons, which means that they can decay if they are isolated.
They decay into a proton, an electron, and a near-massless neutrino in just shy of 15
minutes.
However, the situation is different when they are in a nucleus.
In a nucleus, most neutrons are quite stable.
It’s actually pretty easy to see why.
I’m going to give two answers, the first one will be qualitative and the second one
will give numbers.
Start with an isolated proton and neutron.
Each of them have a distinct mass.
You can convert their individual masses into energy and add them together and that has
some value.
Now take a proton and neutron and have them touch to make a deuteron, which is the simplest
nucleus.
The two of them are bound together, which means that it will take a force to pull them
apart.
You will have to add energy to separate them.
That means from an energy point of view, you can start with the energy of the nucleus and
then add some energy to turn the nucleus into two separate particles.
You can write this as a little equation and you get energy of the nucleus plus the energy
to separate the two particles equals the energy of the separated particles.
Do a little algebra and you see that the energy of the nucleus is >>LOWER<< than the two particles
separately.
So that’s the big answer – the energy of nuclei is generally lower than the energy
of the individual particles that make up the nucleus.
So let’s get specific.
This chart shows the mass of an isolated neutron, proton, electron, neutrino, and the mass of
a deuteron.
Neutrons decay into a proton, electron, and neutrino.
If we put in the values for the mass of the decay, we see that the parent neutron has
a mass higher than the daughters, which means that the decay can proceed.
Now let’s compare the deuteron, which is a nucleus containing a proton and neutron,
to the proton and neutron separately.
As I said a moment ago, the deuteron has a lower mass and this is because you need to
add energy to separate the proton and neutron.
Finally, let’s look at the energy budget if a neutron in a deuteron decays.
You start with a neutron and proton bound together in a nucleus.
The neutron would then decay into a proton, electron and neutrino.
But when you look at how much energy it takes to have two protons, an electron and a neutrino,
you see that the individual particles after the decay have more energy than the deuteron
does.
Accordingly there isn’t enough energy in a deuteron for the neutron to decay.
And this is true for most nuclei.
This is why atomic nuclei are stable.
Good question.
Daniel Pitts, and many others, noticed a speak-o, which is like a type-o but when you’re speaking.
Yes, I inadvertently called Adam Savage of Mythbuster’s fame by the name of Adam Smith,
father of capitalist economics.
Yeah.
It happened.
Mea culpa and all that.
Blame it on an extensive liberal arts education.
Sorry Adam.
Qwaqwa and many others asked how we could be so sure that there aren’t pockets of
antimatter out there in the universe.
Well Qwaqwa, that is a very good question and one I once asked myself.
First let me tell you why it is a sensible question and then why we know it can’t be
true.
To begin with, how do we see galaxies of ordinary matter?
Obviously, by the light they emit.
So, what would an antimatter galaxy emit?
Well, anti-light, of course.
But since light and anti-light are the same thing, an isolated antimatter galaxy would
look exactly like an ordinary galaxy.
So you see that this is an entirely sensible question.
The solution arises because galaxies are made up of more than the stars we see.
Most galaxies are surrounded by huge and diffuse clouds of hydrogen and helium that are much,
much, larger than the obvious part of the galaxy.
These clouds are so big that they bump into one another and even merge.
And that is something we can work with.If an electron encounters a positron, the annihilation
products are always two gamma ray photons each with an energy of 511 kiloelectron volts.
Thus the signature of a matter and antimatter gas cloud will be, among other things, a bunch
of 511 kiloelectron volt photons.
So astronomers turn their gamma ray telescopes to the sky and what do they see?
Essentially nothing.
And that, I’m afraid is that.
Not seeing this very clear signal means that we know with great certainty that antimatter
galaxies are likely non-existent.
Now it is possible that maybe there exists an antimatter galaxy that is not surrounded
by such a cloud, but if they exist, they’d have to be super rare.
And, even if they exist – which is pretty unlikely – they can’t be so common that
that they answer the question of why we see so little antimatter in the universe.
That was an excellent question and one we can answer.
And we still don’t know where all the antimatter went.
Ivaland asks how antimatter reacts with gravity?
Does it fall up?
Hi Ivaland – that’s also a great question.
And there are a couple of answers.
According to Einstein’s theory of general relativity, what creates gravity is energy
and antimatter has the same kind of energy that matter does.
It doesn’t have anti-energy or anything weird like that.
Accordingly, general relativity says that antimatter should react to gravity exactly
like matter.
Thus antimatter should fall down.
But “should fall down” is a theoretical preconception, and I’m skeptical of theoretical
preconceptions.
I’m an experimental scientist, after all.
Luckily there are quite a few ongoing experiments at the CERN laboratory in Europe that are
looking at exactly this question.
Each experiment is performing essentially the same measurement in a slightly different
way.
Basically, they combine a positron with an antiproton to make neutral antihydrogen and
then they simply drop the atoms and watch them to see if they fall down, fly upward,
or do something weird.
When I last spoke to the leaders of one of the experiments, they were predicting results
within a year or so.
So we should definitively know the answer to your question not too long from now.
OK, so that is probably all the time we have for questions.
I wish we had time for more but, sadly, no.
If you’re enjoying the series, please like, subscribe and share, because well sharing
is caring.
And caring is physics.
And how can I say that?
Well, it’s simple.
Caring is part of everything and, even at home, physics is everything.