The 21st Century Particle Principle
By Mark Marchand
I’m not much of a fan of car racing, but demolition derbies amuse me. The intent of these events is straightforward: Keep smashing cars into one another and see what happens. The lone survivor steers his or her car around the arena at the end, usually with parts of the body hanging off and smoke and steam billowing from both ends.
I was thinking of those derbies recently as I watched a PBS documentary about the launch of experiments at the Large Hadron Collider (LHC) straddling the France-Switzerland border. Built and operated by CERN (The European Organization for Experimental Research), the 17-mile underground tunnel and associated equipment is generally accepted as one of the most complex experimental facilities ever built by man. The scientists call it a particle accelerator, or collider. But at its core the mission is simple (sort of like the demolition derbies): Smash stuff together and see what happens.
Since one of the theories behind creating this huge machine was recreating the conditions that existed at the time of the Big Bang, I was amused by stories that circulated as the LHC neared opening in 2008. Some bloggers and journalists suggested that scientists there could accidentally create a black hole, causing all of us to be swallowed up into some infinite corner of the universe. I was relieved when that didn’t happen.
The work that takes place at the LHC is a serious matter. I was delighted to watch usually staid LHC scientists on the PBS show smile broadly as they talked about their work, often using their hands to show the types of reactions that might result from their work. They were breathless and, usually, smiling and laughing. They described in complex terms what they hoped to see as a result of their experiments. Some were nervous, admitting they were not quite sure what the experiments would reveal — which is, I guess, expected when one conducts experiments at this level. If we knew the answer, we wouldn’t need the experiment.
Ever since I took a high school physics class, I’ve been fascinated with the particles that make up everything around us, and, even ourselves. All forms of matter, I learned, are made up of these fascinating, microscopic particles called atoms, which link together to form molecules, which then make up everything that’s solid, liquid, or gaseous. What piqued my curiosity was how these tiny atoms — comprised of even smaller protons and neutrons in a nucleus surrounded by orbiting electrons — could form materials so solid that I could smash a hammer against, say, a metal wall and the tool would just bounce off. Why, I questioned, wouldn’t the hammer sink into that swirling collection of atoms that were orbiting and connecting out of the range of normal eyesight?
The answer is complex, but the easiest way to describe it is that the different atoms “share” some of their electrons, forming a range of “bonds” between atoms and molecules — bonds that in some cases are so strong (like those in a diamond) literally nothing can tear them apart. Others, like the bonds between atoms and molecules in tissue paper, are not so strong.
Once I understood how that worked, I continued to study particles through college, mostly in chemistry classes. I grew to love organic chemistry, which involved all carbon-based matter — otherwise known as the foundation for living things on Earth. I was captivated by the story of how 19th-century German scientist Friedrich August Kekulé envisioned the so-called “ring” structure common to many molecular compounds formed by bonds between carbon atoms. The vision came to him, he says, during a daydream as he thought about a snake circling around and attempting to swallow its own tail. That’s heavy stuff, and it’s true.
Throughout my studies, I continued to base my understanding of physical matter on the fundamental structure of the atom, as first suggested by Danish physicist Niels Bohr. While the model he developed in the early 20th century has been tweaked over time, the essential components of an atom have remained the same: a nucleus of protons and neutrons, and electrons weaving and bobbing around the core.
It was sometime after I finished college and during my early career as a journalist that my safe, sound image of that most fundamental particle, the atom, was shattered. It seems there are more sub-atomic particles responsible for how matter forms and behaves. It was hard for me to accept, but there was an entirely new atomic underworld made up of particles known as quarks, neutrinos, leptons, bosons, gluons, and more. Some are easy to find while others only exist for a short time or can only be found using the most extreme, complex scientific exploration.
And thus (you were hoping I’d get back here, right?) we come all the way back to our brand new LHC over in Europe. The mission of this multifarious machine is to find and study new subatomic particles, helping us better understand the matter around us and why it does what it does. And perhaps we’ll learn new ways to do innovative things with matter. World-changing discoveries ranging from new materials in construction and transportation to new medicines await.
After years of research during the 20th century, scientists found the only way to unearth these new particles was to take apart the atom. You’ve heard of “splitting the atom” as part of the process to get to atomic explosions, right? It turns out that breaking those bonds releases an enormous amount of energy, hence the resulting blasts. The work of colliders takes things a lot further than the lower-tech chain reactions that spark nuclear detonations, or are used to produce energy in nuclear plants.
The LHC works like this: Scientists put together two high-energy beams of protons and shoot them in opposite directions through the LHC tunnels, on a collision course. The dominant force that pushes these beams along comes from huge magnets that constantly accelerate the particles. Think about the force you feel when you hold opposing ends of two magnets together, and multiply that by a factor of thousands. These magnets, powered by high-voltage electricity, get so hot they have to be super-cooled to keep working and prevent melting. Some scientists suggest the low magnet temperatures rival that of the cold in outer space. And, as I noted earlier, to achieve the best collision possible, the particle beams are pushed along at nearly the speed of light.
Once the particles smash together, a set of four different and very sensitive equipment arrays try to detect the different sub-atomic particles and forces that might emerge. These sensors gather so much data it can take weeks or months to determine what just happened.
It was after one of the first real experiments at LHC in 2012 that we heard of the initially tentative and later confirmed discovery of the so-called “God particle,” also known as the Higgs boson. It’s existence was suggested a half century ago by British physicist Peter Higgs and several others. But without a machine like the LHC, they couldn’t prove it — until now. This unstable particle will eventually help us unlock more of the mysteries around why matter behaves the way it does.
There’s much more work to be done, and discoveries to be made, at LHC. It’s been shut down a few times already for re-tooling and repairs, but we’ve only scraped the surface, I suspect. Last month, scientists turned the LHC back on and began circulating the first new protons beams in over a year.
But sub-atomic particles are not the only key to better understanding our world. There’s the relatively new topics of dark matter, and dark energy — which experimental physicists now suggest make up a large percentage of the mass in the universe. The race to find them and prove it is on…but more on that in the future.