Higgs Boson Theory

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? Infact, 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 youthat even in this case, mass is still just boundor confined energy. In the case of theconstituents of the atom, it comes from the Higgs field. So, let's get to the bottom of this whole Higgs business. To understand howall this works, we're going to need to learna bit of quantum field theory. Just the basics for now. We'll get into it inmore detail another time. Now, QFT describes the fundamental particles as excitations in fields, fieldsthat fill our entire universe.

For example, the electron is an excitation in the electron field. Imagine that everypoint in the universe has a certain levelof 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 tothat field at a particular spot, and it's like pluckinga 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, andthese 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 ofthe 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 ofall the components of the atom leave them massless.This masslessness means that particles should travel only at thespeed of light and experience no time. Their clocks should be frozen. But these particles aredistinctly 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 counterclockwiserelative to the direction of motion. We call this left-handednessor right-handedness. Now, that spin constantlyflips back and forth. The electron evolves, meaningit does experience time, so it must have mass. Also, we've weighed it. We've measuredthat mass directly. But a different sortof changeability is the only way that we knowthat the tiny neutrino has mass, and it was themeasurement of those neutrino oscillations the won the2015 Nobel Prize in physics. Now, take the photon. It is definitely massless. It travels at thespeed of light, and it experiences its entire existence in an instant. It undergoes nointernal evolution. It has spin, but thespin never flips. A photon only changes if it bumps into something else. But the photon andthe electron are both just excitationsin their own fields, so why does the electronhave mass and the photon not? Why does the electron evolve? There are differentways to interpret it, but perhaps thesimplest is to say that while the photon cancross the entire observable universe without bumpinginto a single thing, the electron is nevernot bumping into things. There's something in thesubstrate of space everywhere that impedes the electron. It's the Higgs field. To understand how thisworks, we need to come back to this spin flip thing. Here, I need to tell youabout a really odd fact about the universe. It's not ambidexterous. It actually careswhether a particle has left or right-handed chirality. See, left-handed electrons havethis extra little something something compared toright-handed electrons. It's called weakhyper-charge, which by the way was the name of my highschool garage band. It's like regular electric charge, which lets all electrons feelthe electromagnetic force, except in this case, it lets only left-handed electrons feel the weak nuclear force. This cosmic asymmetryis incredibly weird, and it's part of a mysterycalled parity violation. It's an open question why theuniverse cares which direction you're spinning. In fact, it cares so much thatit won't let an electron flip from left to right unless itcan ditch its weak hyper-charge or flip back again unlessit can pick some up. But where does this charge comefrom, and where is it go to? You probably guessed,the Higgs field. The Higgs field is really weird. While most quantum fields hoveraround zero in empty space, the Higgs field hasa positive strength at all points in the universe. There's a little bit ofHiggs in us everywhere. In some stunning quantum weirdness, this complex,multi-component field not only carries theweak hyper-charge, but manages to take on allpossible values of this charge simultaneously. This makes the Higgsfield an infinite source and sink of weak hyper-charge. Now, poor electron is bombardedby a flow of particles into and out of the Higgsfield from all directions, giving and taking away the weak hyper-charge on infinitesimally short time scales.

On its own, the electronwould travel at light speed, but trapped in this Higgs fieldbuzz, the electron feels mass. Honestly, this is apretty wild story. An invisible and infiniteocean of some sort of charge that we'venever heard of all invented so that electronscan be left and right-handed at the same time? How do we know it's true? Well, something likethis must be true, because all of the restof quantum field theory hangs together too well. We conclude that QFTis essentially correct, but it's an incomplete theorywithout 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 otherfields, the Higgs field can vibrate aroundits baseline value, which gives us the boson. This particle actually has nothing to do with giving anything mass.

However, if weobserve the particle, then it means thefield also exists. Finding the Higgs bosonwas the biggest mission of the Large Hadron Collider. Now, that's a topic wellcovered in other places, so just the TLDR. In 2012, the LHC spottedthe debris produced by the decay of anunknown particle, and those decayproducts are consistent with the disintegration of thehighly unstable Higgs boson. It seems verylikely that the LHC did produce the Higgsboson, which in turn would mean that the field exists. The whole story is nowcoming together very nicely. But there's still alot we don't know. The Higgs boson ishopelessly unstable, and it decays in around 10 tothe power of minus 22 seconds, which makes it very difficultto study its actual properties. Could the Higgs fieldalso explain things like dark energy, inflation? There are reasonsto think it might. We'll come back tothose in the future. For now, we'll be delvingdeeper to the mysteries of matter and time in thenext episode of "Space Time." In the last episode,we told you how to build a realastrophysical black hole. Some of you had somepretty heavy questions.

A FastidiousCuber wants toknow how a black hole can grow if anything falling intoit appears to freeze before it crosses the event horizon. So, although an outside observercan never witness anything cross the event horizon, assomething falls to the horizon, the light it emits is redshifted such long wavelengths that it effectivelybecomes invisible. So, infalling stuff doesvanish, and the event horizon that an outsideobserver sees does grow because anythingfalling into the black hole adds to its effective massas seen by a distant observer even before it crossesthe event horizon. Casterverus would like toknow if the potential event horizon that we talkabout is the same thing as the Schwarzschild radius. Well, that's exactly right. The Schwarzschildradius is the radius of the event horizon ofa non-rotating black, and it depends on the mass. Any object thatgets crushed down below its own Schwarzscihldradius becomes a black hole. For the sun, that's3 kilometers. For the Earth, it'saround 9 millimeters. For a person, it'saround 1/10 billionth of the radius of a proton. Gareth Dean asksabout this whole thing about using gravitationalwaves to turn up the core temperature of a star.

OK, so gravitational waves carrya lot of energy, and some of it can get dumped into a starby squeezing and stretching as the gravitationalwave passes by. Now, stars near the coreof a galaxy with merging super massive black holesshould have temperatures raised by an observable amountby the gravitational radiation. There's a link inthe description. WR3ND says, "It only took20 years out of high school to find the smart kid's table." Glad you finallyfound us, WR3ND. We saved you a seat.