Welcome back to Seeker+, I’m Julian and this is part 2 on the Higgs Boson. If you
missed part 1 go check it out because it explains how we even knew to look for the Higgs in
the first place, and why the particle is so important to our entire understanding of the
universe. We basically crammed 60 years of particle physics into one YouTube video.
I am super proud of it. Now though, let’s look at the machine scientists had to design
and build to find the elusive particle.
I’m willing to bet you’ve heard of the equation E=mc2, or energy equals mass times
the speed of light squared. Einstein's famous equation has some big implications for particle
physics. For example, we measure the mass of subatomic particles with a unit called
the electron Volt. 1 electron Volt is how much energy an electron gains as it’s accelerated
through an electric field with one volt of potential difference. It may seem weird to
use a unit of energy to also describe mass, but it makes sense when you remember mass
and energy are related. An electron has a mass of about half a million electron-volts.
A proton has a mass of about a billion electron volts, or 1 Giga electron volt, GeV.
Since mass and energy are related, it also means we can make heavier particles out of
lighter ones, if we give those lighter ones enough energy. Before we actually spotted
the Higgs Boson, scientists had calculated that it probably had a mass around 115 to
140 times that of a proton. So to make something that massive out of protons, we need to get
them moving really really fast. Like, 99.9999991% the speed of light.
But why use protons in the first place? Why not use something heavier that we don’t
have to get moving as fast? Or electrons and their antimatter counterparts, positrons?
Or protons and antiprotons? Well first off, protons are available in abundance and can
be made relatively easily by breaking hydrogen gas down with an electric field. Antimatter,
on the other hand, is not cheap or easy to make. That’s putting it lightly. By one
estimate it costs $25 billion dollars to make 1 gram of positrons, and $3 quadrillion dollars per gram
of antiprotons. It’s the most expensive stuff on earth. Even more expensive than printer ink.
Would you rather use that or like, a bottle of hydrogen gas that costs around 100 bucks?
Lots of protons also means more collisions which means more data. Protons are stable,
so they won’t decay into other stuff while they’re zipping around an accelerator. They’re
also charged, which means we can get them moving really fast using an electric field,
and we can steer them and focus them into a beam with magnets. It’s not entirely good
news. Protons are made of smaller elementary particles, quarks, which are held together
by a gluon yarn ball. The inside of a proton is total chaos; it’s makeup is always in
flux. There could even be antiquarks that can pop up in there spontaneously. When you
smash two protons together at high energy, what actually collide are some of the guts
of the protons, and because they’re always changing you don’t know exactly what’s
going to hit what, or at what energy. By contrast, an electron isn’t made up of smaller parts,
it's as fundamental as it gets. So when you smash one into a positron, you know exactly
what to expect. My favorite comparison is an electron-positron collider is like a scalpel,
while a proton-proton collider is like two garbage cans banging together. Still there
is an upside to the messiness of smashing protons. Because the outcomes are so unpredictable,
they’re great for exploring a lot of possibilities. And as it happens, the Higgs boson can be
created from merging gluons, and as we’ve covered protons are just silly with those.
Still, when the search for the Higgs began there was nothing that could get them going
fast enough. So scientists set to work and in the 1980s and they proposed the biggest, baddest
proton smasher imaginable. No, not the Large Hadron Collider, I’m talking about America’s
Superconducting Super Collider. Sounds pretty super, right? The SSC, as it’s known
for short, was supposed to be an absolutely mammoth machine. It would have been a ring
nearly 90 kilometers around running underneath Texas, capable of smashing protons together
with an energy of 40 trillion electron volts. For reference, the most powerful collider
the U.S. has built to this day didn’t quite hit 1 trillion electron volts. It was supposed
to be so absurdly powerful that the governments of Europe nearly scrapped their plans for
their own accelerator.
Fortunately for us, they didn’t. An Italian physicist named Carlo Rubbia was convinced
that the Americans wouldn’t see the SSC through and managed to keep the European project
alive. Rubbia’s instinct turned out to be correct. In 1993, the U.S. Congress withdrew
funding for the SSC, in part because the project was over budget and no other nations wanted
to pitch in. Japan was one of the most likely partners but the competing auto industries
of the two countries put the partnership on thin ice. It fell through in 1992 when President
George H. W. Bush visited Japan and was going to ask Prime Minister Miyazawa for funding,
but instead he, well, he vomited on the Prime Minister. Back in the U.S., it also didn’t
help that physicists in other fields were griping publicly about how much funding the
SSC was soaking up. Some even celebrated its demise and apparently this is still a sore
spot within the U.S. physics community. Europe’s planned accelerator wasn’t nearly as powerful
as the SSC: its collisions would max out at 14 trillion electron volts as opposed to
40. But hey, it was getting built, and an actual accelerator beats a non-existent one any day
of the week.
Europe’s accelerator is, of course, the Large Hadron Collider, or LHC. Hadrons are
particles that interact with the strong force, like protons, in case you ever wondered. The
LHC is often called the most complex machine ever built by humans, which is quite a claim.
We did a whole episode on the most expensive machine ever built, the International Space
Station, so to say something is more complex than that, is no small boast. When you consider
everything that went into the LHC, you start to understand just how mind-boggling the engineering
is. It’s the largest machine ever built, it’s basically a ring 27 kilometers around
and buried 100 meters under the Swiss and French countryside. Over 9,000 magnets run
the entire length, and not like refrigerator magnets, but incredibly strong electromagnets
that have to be chilled to less than 2 degrees above absolute zero, colder than the vacuum
of space. At that temperature they become superconductors, meaning tons of electricity
can course through them without resistance, creating magnetic fields that can steer those
protons as they’re whipping around at nearly light speed. Those protons, by the way, are
actually traveling around the ring inside tubes where the atmospheric pressure is less
than the surface of the moon. You don’t want your protons bumping into air molecules
and slowing down, right? There are two of these tubes, and protons travel through them
in opposite directions. They’re brought together so they can collide head on inside a
detector. The LHC has 4 large detectors, and 2 of them were important for finding the Higgs.
One of those, ATLAS, is the largest detector ever built for a collider by volume. It’s
46 meters long and weighs 7,000 metric tons. The other, CMS, is more compact, that’s
actually what the C stands for. But it’s only “compact” compared to ATLAS, it’s
still huge and it actually weighs twice as much! To make things more complicated, it
had to be designed in pieces that could be transported through medieval European cities
on the way to the construction site. Funny story about that construction site: when builders
started digging, they uncovered an ancient Roman city and the whole project had to be
put on hold for 6 months while archeologists sorted things out.
Finally though in September of 2008 the LHC was completed and switched on. Everything
went smoothly… for about 10 days. Then a power cable blew and 53 of the superconducting
magnets that had to be kept super cold stopped being all of those things. They overheated
and they damaged their coolant pipe and the LHC had to pause operations for over a year while
everything was fixed. Just before it came back online, the LHC suffered another setback
when an electrical substation that powered part of the magnet cooling system failed,
only this time, it wasn’t caused by a faulty wire, but a piece of baguette. Who could be
responsible for such a thing? Was it a Frenchman upset at science for taking some mystery and
romance out of the universe? The 1993 U.S. Congress that was bent on stopping this accelerator
too? The Higgs Boson itself that wanted to remain undiscovered for its own personal reasons?
No, in all likelihood the culprit was… a pigeon. Yeah, the most complicated machine
we’ve ever made was taken out of commission by one clumsy bird, albeit for like, a day.
When everything was fixed in late 2009, the LHC started up again, but only at half the
power it was originally designed for. Still, it was enough to finally hunt for the Higgs
Boson. So, what was it that finally gave it away? What was the smoking gun scientists
spotted that confirmed our ideas on how the universe worked?
We’ll save that for the next episode. For now I hope you’re enjoying this series on
the Higgs Boson, let us know if there’s anything else that you'd like to see in the quantum realm
that we can maybe do a deep dive on! Don’t forget to subscribe and I’ll see you for
the next episode of Seeker+.