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.
