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When you step on a scale and look down at the number that shows up.
What that number is telling you is how much force the mass of your body exerts on the
ground.
It’s simple Newtonian mechanics, Force equals mass times acceleration.
Gravity exerts the acceleration on the mass of your body, which creates force.
That’s your weight.
So weight is probably easy enough to understand.
But mass is a little more nebulous.
If you were floating in space far away from earth, you would have essentially no weight,
but you would still have the same mass as you did standing on that scale.
Where does the mass of your body come from.
Well, the mass comes from all the atoms in your body that individually have a mass.
Where does an atom’s mass come from?
Well, this is interesting because the mass of atoms, at its core is really energy.
In fact, all mass is Energy.
This is exemplified in Einstein’s famous mass-energy equivalence equation E=MC^2.
Mass is interchangeable with energy, and the constant, C squared, or speed of light squared,
is the conversion factor.
99% of the mass of an atom is contained in the binding energy within the nucleus.
This energy is a result of one of the four fundamental forces of nature, called the Strong Force,
which keeps the protons and neutrons glued together in the nucleus of atoms.
That’s where most of your body’s so called mass resides.
But it turns out that some of your mass, about 1%, is contained in the mass of the subatomic
particles that make up the atoms, these are the electrons that form a cloud around the
nucleus, as well as the quarks that make up protons and neutrons.
So, now the question is how do these subatomic particles have an intrinsic mass?
If mass is energy, then what is the mechanism that confers this energy to these fundamental
particles?
This is where the Higgs Field comes into the picture.
This field is everywhere in spacetime.
But most explanations of how this field confers mass can’t avoid getting highly technical,
talking about symmetry breaking and other advanced mathematical concepts.
In this video, I’m going to attempt to explain how the Higgs field confers mass, in an intuitive
way so whether you’re a math geek or not, you will hopefully get a very good intuitive
understanding of what’s really going on.
That’s coming up right now…
I’ve been wanting to make this video for a while, and I think you’re going to find
it very interesting.
Before we get into it, I want to thank our sponsor Blinkist that helped make this video
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Now where were we…
To understand how the Higgs field works, we have to first understand what our best theory
describing all the matter in the universe, the standard model of particle physics, is
trying to tell us.
This theory describes all fundamental particles in the universe as excitations in quantum
fields.
So, for instance, an excitation of the electromagnetic field would be a photon, an excitation of
the electron field is an electron, and an excitation in the quark field would be a quark,
etc.
These are waves, but when they are well localized, as in a measurement, they appear to us as
particles.
These fields span all of spacetime, in all directions.
The animation you are seeing here is a 2D representation for visualization, but the
fields would be in three dimensions.
Every type of matter and force particle has its own field.
So all the fundamental particles of the standard model would be represented by different fields.
All these fields, when they are in their ground state, that is, their lowest energy state,
even when no excitations or particles are present, always have some vibration.
Due to the Heisenberg uncertainty principle, particles are constantly being created and
annihilated.
These are virtual particles that exist for such a short period of time, that they cannot
be measured.
They borrow energy from the vacuum when they are created and give it right back very quickly
when they are annihilated.
But this flurry of energetic activity, for each field, collectively adds up to zero net
real particles.
Real particles are created only when enough energy is transferred to these fields from
some other field to cause an excitation.
These excitations are the real particles.
And since these are quantized fields, any excitation occurs only in set quantities.
So for example, an excitation in the electron field would have to occur in integer multiples
of 0.511 mega electron volts, or MeV, which is the mass of one electron.
So the field can have energy of 1.022 MeV, which would be the energy of two electrons,
or any other multiple of 0.511, but not for example 0.7 MeV, which would not be an integer
multiple of 0.511.
But the electron only has this intrinsic mass of 0.511 MeV because of its interaction with
the Higgs field.
Without this interaction, an electron would be massless.
It would have energy but only in the form of momentum, just like photons.
This massless electron would be like a charged photon, and move at the speed of light.
In fact, without the Higgs field, all the other fundamental particles of the standard
model would also be massless, with the possible exception of neutrinos.
So the question is how does this mass come about?
To understand this, we have to understand the concept of vacuum expectation value of
the various field.
What does this mean?
Let’s imagine for a minute, as if there were no Higgs field.
If we then took any of the fields and put them inside an empty box, like the electron
field, and if we then weighed the box, we would find that box would have no weight.
In other words the field would have no mass, even though the virtual electrons would be
present throughout it.
Similarly, all the other fields of the Standard Model would also have no mass inside the empty
box, just quantum fluctuations.
But, here’s the big kicker, there is an exception to this rule, the Higgs Field.
It is unique because the Higgs Field in empty space, unlike every other field, has a net
positive mass.
Its mass is NOT zero in empty space.
So if were to weigh the box with the Higgs field inside, it would have a weight.
The Higgs field in empty space has a mass.
This is called the vacuum energy.
A more technical term for this is the vacuum expectation value (v.e.v.) of the Higgs field.
It is nonzero.
It is in fact 246 GeV.
This is just the value that we would "expect" the Higgs Field to have when it is in its
vacuum state, or in its lowest energy state.
Now as I said earlier, quantum fields can interact with each other.
What this basically means is that anything that interacts with the Higgs field now effectively
interacts with this new vacuum expectation value.
And that interaction means energy.
And since energy and mass are equivalent, the form this interaction energy takes is
indistinguishable from the form of energy associated with a rest mass.
So when a fundamental particle interacts with the Higgs field, it gains an energy or intrinsic
mass.
Without a Higgs field, the electron would also be massless like photons and travel at
the speed of light.
However, since the electron is coupled to a field with a positive value everywhere in
the universe, individual electrons are constantly interacting with the Higgs field.
This constant interaction effectively slows the electron down.
So if you apply a force to an electron, you can imagine a sort of push-back from the Higgs
field that causes the electron to resist acceleration.
This property is what we call inertial mass.
The electron’s behavior in the vacuum, is that of a particle with a well-defined rest
mass of 0.511 MeV.
This rest mass is determined by the strength of the coupling or interaction between the
electron and the Higgs v.e.v.
It’s like the mass of the Higgs field is shared with any other field that interacts
with it.
How much mass an excitation or particle in any given field has, depends on its coupling
constant.
The fields of all massive particles are coupled to the Higgs field to some degree.
The larger the coupling constant, the more mass its particles will have.
Without the Higgs field, none of the other particles would have an intrinsic mass.
The Higgs Field is like a thick gravy and if you try to run a spoon through it, it feels
heavy compared to moving the spoon through air.
So every elementary particle with mass interacts with this gravy in some way.
The particles of the standard model that have mass, such as electrons, quarks, and W and
Z bosons are coupled to the Higgs field, …while the fields of massless particles,
like photons and gluons are not.
Why are some particles coupled, meaning why do some particles interact with the Higgs
field, while others do not?
We’re not sure.
This just appears to be the way the universe works.
The photon happens to be one of the particles that does not interact with the Higgs Field
and so it remains massless. And moves at the speed of light.
The mechanism of the Higgs Field giving out mass to other particles is called "symmetry breaking"
This is a complex subject but if you want to know more about symmetry breaking,
I made a video about it right up here.
Now, I should add a note about neutrinos.
The Standard Model predicts that they should be massless, but measurements seem to indicate
that they do have a very tiny mass.
We don’t know the origin of that mass.
It could be that they also interact with the Higgs, but no one really knows for sure.
Now, I want to reiterate what I said at the beginning.
The Higgs field is only responsible for about 1% of the mass of all the matter in the universe
that we can see. The vast majority of the mass is due to the energy of the strong force
which keeps the nuclei of atoms tightly glued together.
Yet, this 1% is essential to have the kind of universe we have.
In a simple hydrogen atom, for example, the radius of the electron’s orbit is inversely
proportional to its mass.
In a universe with no Higgs Field, a massless electron would have an infinite radius, meaning
no atoms would form at all. In addition,
differences in particle mass is also responsible for the decay of free neutrons to protons. This is called "Beta Decay."
Without the Higgs field, the universe may not have any protons at all.
So this tiny 1% mass contribution, turns out to be responsible for 100% of the universe
we happen to have.
I’d like to thank our Patreon supporters who make these animations possible.
Thank you very much.
I’ll see you in the next video my friend.