Why We Need the Large Hadron Collider

Welcome back to Seeker Plus, I'm Julian and this is part two on the Higgs boson. If you missed part one, 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 the equation E equals mc squared 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. One 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 that 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 one 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. And that's putting it lightly. By one estimate, it costs $25 billion to make one 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 a hundred 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. And 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 glue-on yarn ball sort of type deal. The inside of a proton is total chaos. Its makeup is always in flux. There could even be anti-quarks 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 is going to hit what or with 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 glue-ons. 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 in the 1980s and proposed the biggest, baddest proton smasher imaginable. No, not the Large Hadron Collider. I'm talking about America's superconducting supercollider. Yeah, 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 sucking 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 its 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. That's 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 four large detectors, and two 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 in the name 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 designed in pieces that could be transported through medieval European cities on the way to the construction site. And funny story about that construction site, when builders started digging, they uncovered an ancient Roman town, and the whole project had to be put on hold for six months while archaeologists 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. 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 of the mystery and romance out of the universe? Was it the 1993 US Congress that was bent on stopping this accelerator too? Was it 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 you'd like to see in the quantum realm that we could maybe do a deep dive on. Don't forget to subscribe, and I'll see you for the next episode of Seeker Plus.