In 2012, a new particle was
discovered by the Large Hadron Collider. Physicists believe that the
elusive Higgs boson has finally been found. But what's the big deal with
this whole Higgs thing, anyway? [THEME MUSIC] We saw in a previous
episode that most of the mass in your body, in
fact, the mass of anything that's made of
atoms, doesn't come from the mass of the
elementary particles. The electrons, and
the quarks that comprise protons and neutrons,
do seem to have intrinsic mass, but this is only run 1%
of the mass of the atom. Most of the atom's mass is the
confined kinetic and binding energy of those quarks. Now, today I want to talk about
this so-called intrinsic mass of the elementary particles. I want to show you
that even in this case, mass is still just bound
or confined energy. In the case of the
constituents of the atom, it comes from the Higgs field. So, let's get to the bottom
of this whole Higgs business. To understand how
all this works, we're going to need to learn
a bit of quantum field theory. Just the basics for now. We'll get into it in
more detail another time. Now, QFT describes the
fundamental particles as excitations in fields, fields
that fill our entire universe. For example, the
electron is an excitation in the electron field. Imagine that every
point in the universe has a certain level
of electron-ness. In empty space, that
level hovers around zero. But even in a vacuum, the
electron field is there. But now, add some energy to
that field at a particular spot, and it's like plucking
a guitar string. The field vibrates, and that
vibration is our electron. And it's not just electrons. Every elementary
particle is a vibration in its own field, and
these vibrations and fields interact with each other,
transferring energy, momentum, charge, et cetera, between
particles and fields. Now, this is a very
simplistic explanation of a theory that has
produced an astoundingly accurate description of
the subatomic universe. Given its incredible
success, it was strange that quantum field theory,
as it stood in the 1950s, gave a perfect description
of the electron, and yes predicted that the
electron should have no mass. The basic QFT equations of
all the components of the atom leave them massless. As we'll see in the
next couple of episodes, this masslessness
means that particles should travel only at the
speed of light and experience no time. Their clocks should be frozen. But these particles are
distinctly not timeless. They evolve. Take the electron. It has this type of
intrinsic quantum spin that we call chirality,
and this can either be clockwise or counterclockwise
relative to the direction of motion. We call this left-handedness
or right-handedness. Now, that spin constantly
flips back and forth. The electron evolves, meaning
it does experience time, so it must have mass. Also, we've weighed it. We've measured
that mass directly. But a different sort
of changeability is the only way that we know
that the tiny neutrino has mass, and it was the
measurement of those neutrino oscillations the won the
2015 Nobel Prize in physics. Now, take the photon. It is definitely massless. It travels at the
speed of light, and it experiences its entire
existence in an instant. It undergoes no
internal evolution. It has spin, but the
spin never flips. A photon only changes if it
bumps into something else. But the photon and
the electron are both just excitations
in their own fields, so why does the electron
have mass and the photon not? Why does the electron evolve? There are different
ways to interpret it, but perhaps the
simplest is to say that while the photon can
cross the entire observable universe without bumping
into a single thing, the electron is never
not bumping into things. There's something in the
substrate of space everywhere that impedes the electron. It's the Higgs field. To understand how this
works, we need to come back to this spin flip thing. Here, I need to tell you
about a really odd fact about the universe. It's not ambidexterous. It actually cares
whether a particle has left or right-handed chirality. See, left-handed electrons have
this extra little something something compared to
right-handed electrons. It's called weak
hyper-charge, which by the way was the name of my high
school garage band. It's like regular
electric charge, which lets all electrons feel
the electromagnetic force, except in this case, it lets
only left-handed electrons feel the weak nuclear force. This cosmic asymmetry
is incredibly weird, and it's part of a mystery
called parity violation. It's an open question why the
universe cares which direction you're spinning. In fact, it cares so much that
it won't let an electron flip from left to right unless it
can ditch its weak hyper-charge or flip back again unless
it can pick some up. But where does this charge come
from, and where is it go to? You probably guessed,
the Higgs field. The Higgs field is really weird. While most quantum fields hover
around zero in empty space, the Higgs field has
a positive strength at all points in the universe. There's a little bit of
Higgs in us everywhere. In some stunning
quantum weirdness, this complex,
multi-component field not only carries the
weak hyper-charge, but manages to take on all
possible values of this charge simultaneously. This makes the Higgs
field an infinite source and sink of weak hyper-charge. Now, poor electron is bombarded
by a flow of particles into and out of the Higgs
field from all directions, giving and taking away the weak
hyper-charge on infinitesimally short time scales. On its own, the electron
would travel at light speed, but trapped in this Higgs field
buzz, the electron feels mass. Honestly, this is a
pretty wild story. An invisible and infinite
ocean of some sort of charge that we've
never heard of all invented so that electrons
can be left and right-handed at the same time? How do we know it's true? Well, something like
this must be true, because all of the rest
of quantum field theory hangs together too well. We conclude that QFT
is essentially correct, but it's an incomplete theory
without a mass-giving field. The Higgs field is the best,
least silly option to do this. But how do we prove it? Enter the Higgs boson. Just like the other
fields, the Higgs field can vibrate around
its baseline value, which gives us the boson. This particle
actually has nothing to do with giving anything mass. However, if we
observe the particle, then it means the
field also exists. Finding the Higgs boson
was the biggest mission of the Large Hadron Collider. Now, that's a topic well
covered in other places, so just the TLDR. In 2012, the LHC spotted
the debris produced by the decay of an
unknown particle, and those decay
products are consistent with the disintegration of the
highly unstable Higgs boson. It seems very
likely that the LHC did produce the Higgs
boson, which in turn would mean that the field exists. The whole story is now
coming together very nicely. But there's still a
lot we don't know. The Higgs boson is
hopelessly unstable, and it decays in around 10 to
the power of minus 22 seconds, which makes it very difficult
to study its actual properties. Could the Higgs field
also explain things like dark energy, inflation? There are reasons
to think it might. We'll come back to
those in the future. For now, we'll be delving
deeper to the mysteries of matter and time in the
next episode of "Space Time." In the last episode,
we told you how to build a real
astrophysical black hole. Some of you had some
pretty heavy questions. AFastidiousCuber wants to
know how a black hole can grow if anything falling into
it appears to freeze before it crosses the event horizon. So, although an outside observer
can never witness anything cross the event horizon, as
something falls to the horizon, the light it emits is red
shifted such long wavelengths that it effectively
becomes invisible. So, infalling stuff does
vanish, and the event horizon that an outside
observer sees does grow because anything
falling into the black hole adds to its effective mass
as seen by a distant observer even before it crosses
the event horizon. Casterverus would like to
know if the potential event horizon that we talk
about is the same thing as the Schwarzschild radius. Well, that's exactly right. The Schwarzschild
radius is the radius of the event horizon of
a non-rotating black, and it depends on the mass. Any object that
gets crushed down below its own Schwarzscihld
radius becomes a black hole. For the sun, that's
3 kilometers. For the Earth, it's
around 9 millimeters. For a person, it's
around 1/10 billionth of the radius of a proton. Gareth Dean asks
about this whole thing about using gravitational
waves to turn up the core temperature of a star. OK, so gravitational waves carry
a lot of energy, and some of it can get dumped into a star
by squeezing and stretching as the gravitational
wave passes by. Now, stars near the core
of a galaxy with merging super massive black holes
should have temperatures raised by an observable amount
by the gravitational radiation. There's a link in
the description. WR3ND says, "It only took
20 years out of high school to find the smart kid's table." Glad you finally
found us, WR3ND. We saved you a seat. [MUSIC PLAYING]
This is my new favorite YouTube channel. I kind of prefer the old host but the new one is growing on me. Their series on relativity is a must watch.
this is actually... really good.
Good but I don't think this really explains how this interaction gives rise to mass. The top comment here is one of the better explanations. Basically, it is a relatively simple exercise to work out the effective mass of a photon that is stuck between two mirrors (the mass you get is m=E/c2, ie E=mc2). It has an effective mass because if you try to push on the mirrors the photon exerts more pressure on the front mirror than the back, which simulates inertia. The Higgs mechanism works the same way. Each chirality flip from the weak hypercharge exchange described in the video is associated with the massless particle getting reflected back and forth by the higgs field just like in the photon & mirror example.
It's nice learning something about a subject you thought you were top notch on.
I like that it was really informative, without being too technical, but technical enough that anyone who has watched a few documentaries could follow along. Good stuff. Frequently a show doesn't balance this fine line, for no fault of their own since nobody has the same level of understanding.