Hello everyone, welcome back to Seeker+, I’m your host Julian Huguet. And I want to ask, what
does the 4th of July mean to you? If you’re an American, it probably brings to mind backyard
cookouts and fireworks. If you’re not American, it’s probably a pretty unremarkable date.
But no matter where you live in the world, July 4th 2012 was an important day for you,
even if you don’t know it. On that day the European Organization for Nuclear Research,
better known as CERN, announced they had evidence of a particle that was likely the long-theorized
Higgs Boson, often referred to in the news media as “the God Particle”. We’re coming
up on the 10th anniversary of its discovery so I wanted to take a more in-depth look at
the Higgs Boson. In this series, we’re going to talk about how scientists even knew to
look for it, how they found it, and what it means for the future of particle physics.
But first, let's talk about that nickname, “the God Particle,” a moniker many physicists
absolutely hate.
Sure it’s a sexy name and it looks good on a headline or YouTube title. It’s also led
people to think that maybe the discovery of the Higgs Boson has something to do with the
search for God. But it doesn’t, it’s discovery isn’t evidence of any sort of higher being
and that’s not why scientists were searching for it. In fact, the nickname was sort of a joke.
See, finding this particle took nearly 50 years and the most complex machine humankind
has ever built. It was such an elusive thing that one physicist, Nobel laureate Leon Lederman,
called it “The Goddamn Particle.” That’s what he was going to call his 1993 book about
it, but the publisher didn’t like that so he dropped the “damn” from the title.
The book was a hit, the name stuck, and now physicists have to keep correcting people
about it forever. Now before you go accusing me of using that for clickbait in the title,
one, don’t blame me, blame Leon Lederman’s publisher. And two, you’re absolutely right,
but hey, I made a point to clear it up right away. That counts for something, right?
The particle’s discovery may not resolve the debate about God, but it was nonetheless
a huge advancement of our understanding of the universe. The Higgs Boson made the behavior
of other particles we’ve discovered make sense, it explained how atoms could exist
and stars could shine. It was the last big piece of a fantastically complex jigsaw puzzle,
and it’s not like scientists had a picture on a box to guide them. So how did they know
to look for it?
Before diving in though, I have to give you a primer on particle physics so we’re all
on the same page. Don’t worry it’s going to be totally easy, partly because I’m going
to oversimplify it just a bit. And when we get to the end, you’ll be a mini-expert on the subject.
Think of how fun you’ll be at parties! Ok, ready? I mentioned the Higgs Boson was
the last piece of a puzzle, and in a literal sense, that’s true. It was the last particle
predicted by the Standard Model of Particle Physics, which is our framework for organizing
and describing elementary particles. You know how the periodic table of elements arranges
chemical elements based on how big they are and how they behave? Well, the standard model is
like that, but with the particles even smaller and more fundamental than atoms. The Standard
Model is split into two main groups. One group is the fermions, which are particles like
electrons and quarks, the building blocks of protons and neutrons. The other group is
the bosons, which particles use to exchange energy with each other. You can think of bosons as the carriers
of the four fundamental forces of nature. Well, maybe they carry all four, but definitely
three. Photons, the particles that we can see as light, carry the electromagnetic force. Gluons
carry the strong nuclear force, they’re what binds those quarks together into protons
and neutrons, and they're also what binds protons and neutrons together in an atom’s nucleus.
It’s like they glue everything together, get it, “glue-ons”? The Weak Nuclear force
is carried by W and Z bosons and it causes subatomic particles to decay into other particles.
And there’s a hypothetical boson called the graviton which could be responsible for
gravity, but we haven’t found it yet. Photons, Gluons, and the W and Z bosons are
called gauge bosons. Then there’s the Higgs boson, which is special. It’s not the boson
itself that’s so important, but its existence points to something larger that solves a big
problem with the standard model.
You may have noticed that two of the forces carried by bosons have the word “nuclear”
in them, the strong nuclear force and the weak nuclear force. That’s because they
only work over incredibly short distances, within the nucleus of an atom. The other two
forces, electromagnetism and gravity, are extremely long ranged. That’s because photons
and the hypothetical gravitons have no mass, and Einstein tells us that if something has
no mass it must travel at the speed of light. Why two forces can travel across the universe
while the other two can’t make it outside of an atom was a huge mystery for physicists
and it’s even caused some serious drama. In 1954, one physicist, C. N. Yang, gave a
lecture arguing that all forces could arise from a concept called symmetry, which I’ll
spare you, don't worry. I'm not going to get into because I think we already are hitting the limit of how much
jargon I can put in one episode. Anyway, renowned particle physicist Wolfgang Pauli was in attendance
and he kept pestering Yang. Pauli knew that Yang’s explanation of attributing all forces
to symmetries meant all bosons wouldn’t have a mass and would therefore have unlimited
range. Pauli knew that wasn’t the case so Yang’s idea couldn’t work. He shouted
at Yang repeatedly “What is the mass?” and when Yang said it was complicated and
he and his colleague Robert Mills just couldn’t figure it out, Pauli told him that wasn’t
a good enough answer. Yang got so flustered, he actually stopped his lecture halfway through
and took a seat. Yang and Mills would get the last laugh, because it turns out
their idea that symmetries give rise to forces was actually right. Their 1954 paper about
this concept was the starting point for the Standard Model, and many years later, it was
discovered gluons actually don’t have a mass, but they interact with each other and
form something like a big ball of quantum yarn that’s confined to an atom’s nucleus.
The weak nuclear force though is different, and amazingly we were put on the right track
to figuring it out by a couple guys who were just making stuff up. You see, a neutron can
decay into a proton. Likewise a proton can change into a neutron, which is a really important
step in nuclear fusion, the process that powers stars. This is where the weak force comes
in. Scientists needed to explain how a neutron, which as the name suggests has a neutral electric
charge, could change into a positively charged proton and vice versa. So in 1957, a physicist
and Harvard professor named Julian Schwinger made up the W bosons pretty much out of thin air. He didn’t
have any evidence that they existed, he just came up with a concept that seemed to work.
Here’s Schwinger’s idea: when a neutron decays, one of the quarks it’s made of changes,
emitting a negatively charged W- boson and thus conserving overall charge. The W- boson
quickly decays into an electron and an antineutrino. Protons are the same, just flip all the minus signs
to plus signs. To explain the W boson’s short range, he gave it a mass, which, again, he
just made up because he knew the weak force had a short range, he didn’t derive it mathematically.
He also combined the electromagnetic force and the weak force, creating what Pakistani
physicist Abdus Salam would later dub the electroweak force. By the time Schwinger’s
paper was published though, famous physicist C.S. Wu had already performed a groundbreaking
experiment that showed for the first time that a kind of symmetry could be broken, which
meant symmetry could still give rise to the weak force but allow the bosons to have a
mass. Wu’s experiment also showed the weak and electromagnetic forces couldn’t be joined
the way Schwinger suggested. Schwinger didn’t let go of his idea, instead he did what any
great professor does: he gave the problem to his grad student Sheldon Glashow. Glashow
figured he could make the two forces reconcile by inventing yet another particle, the neutral
Z boson. Again there was no evidence of W and Z bosons, they wouldn’t be discovered
for another 20 years.
Making up bosons and just claiming they have mass is all well and good, who doesn’t do
that for fun, right? But at some point, someone’s going to have to explain where that mass comes
from, what exactly is breaking symmetry? In 1964, 6 different scientists all landed on
the answer within months of each other. They suggested that there might be some sort of
field, present at all times and permeating the entire universe. This field could interact
with bosons, giving them mass and slowing them down. Peter Higgs was one of those scientists,
and although he wasn’t the first to come up with the concept, he took it a little further.
After his paper was initially rejected, Higgs submitted it to another journal with a couple
of added paragraphs, stating it should be possible to excite this field and create a particle.
That’s right, because of a minor rewrite he suggested what we now call the Higgs Boson,
although Peter Higgs himself doesn’t seem too fond of the name. He refers to it as the
“So-called Higgs Boson” and to credit the other physicists who independently came
up with the same idea, he proposed using their initials and calling it the ABEGHHK’tH mechanism.
Can’t imagine why that didn’t stick.
Here’s the thing though, when those six scientists proposed this mechanism, none of them realized
how important it would be. They were all trying to solve an entirely different problem and
get around something called the Goldstone theorem that stated even when symmetries are
broken you should still get a massless particle, which would have shown up in experiments by
that point. A field rectified that, and the scientists suggested maybe it could explain
the strong force too? And that was it, nobody really took notice. The major breakthrough
came three years later when a physicist named Steven Weinberg put it all together. Weinberg
was trying to explain the strong force with this field and give mass to gluons, not knowing
as we know now that they’re massless so he was getting nowhere. Then one day, Weinberg
was cruising along in his Camaro when it hit him. What if instead of focusing on the strong
force, he used this field to explain the short range of the weak force instead? What if it
gave mass to the W boson? I have to emphasize at the time, almost no one took the idea of
W bosons seriously. But Schwinger realized the ideas fit together perfectly and could
unify the electromagnetic and weak forces after all. It remains, I am certain, the most
intelligent thing anyone has ever done in a Camaro, which usually involves jumping off
of ramps into hay bales. What was the physics world’s reaction to this earth-shattering
revelation? Crickets. The idea finally started gaining traction in 1971 when another scientist
showed that it all made mathematical sense. Soon the first hints of the Z boson were seen,
and Weinberg's paper, which mistakenly credits Higgs first among the six scientists, quickly
became the most cited paper in high energy physics and would be for the next 30 years.
Hopefully, I’ve made it easy now to see why. Suddenly, this hypothetical field could make
everything work together beautifully, it could even explain the mass of other particles like
electrons and quarks. And because of the particle Higgs proposed it was actually possible to
confirm if it existed, we just had to find the Higgs. The standard model was starting
to take shape and the path forward for the next 40 years of particle physics was set.
But how does one go about finding a new particle? By smashing particles together at nearly the
speed of light, that’s how!
We’ll talk about that on the next episode of Seeker+. I just want to say if you made
it this far, congrats! We covered a lot of ground at nearly light speed and
honestly, I barely skimmed the surface. The next video is going to be less concept heavy
and it's going to be about the fun stuff like smashing atoms. If you want even more in-depth talk
of particles and quantum stuff like this, let us know in the comments and be sure to subscribe.
I’ll see you for the next Seeker+.