Williams College

Super Collider: The Discovery Machine

What is the Large Hadron Collider?

The LHC will give us a deep and powerful look at the nature of our physical world. By colliding high-energy protons (and, in a separate experiment, lead ions) that are traveling at nearly the speed of light, we will recreate some of the conditions that existed at the Big Bang, the likely beginning of our universe. Detectors will track the sub-atomic debris from the collisions, giving us a new understanding of the world of particle physics — the unimaginably small building blocks that comprise the whole universe. By extension, these insights will help us understand the universe on a large scale, including things like galaxies, black holes, dark matter, and solar systems.

So the LHC could shed some light on the nature of mass. Why is that important?

Mass is all around us; it is something we experience all the time, and most of us take for granted. Without mass, particles could not coalesce to form the things we know, like stars, water, planets and people. Yet, paradoxically, scientists do not actually understand mass. Where does it come from? How do particles acquire mass? Why are some particles very heavy, while others have no mass at all? These are very basic questions, without the answers we cannot fully comprehend our physical world.

Is that where the elusive Higgs Boson comes in?

Exactly. Many physicists have theorized that particles acquire mass by moving through a universal field called the Higgs field. Just as walking through a muddy field would make you heavier, the Higgs field gives particles mass, and slows them down. Although the Higgs field is not directly measurable, the LHC has the potential to excite the field so it releases detectable particles called Higgs Bosons.

No one has ever found a Higgs Boson. It is the last undetected particle of our current theoretical framework of particle physics.  If the LHC detects the Higgs Boson, it will prove the existence of the Higgs field, supporting our current scientific model. This will close an important chapter of the development of elementary particle physics.

What if you don't find the Higgs Boson?

Many expect that we will turn on the LHC and see the elusive Higgs Boson right away. However, an equal number of theoreticians think we simply might not see Higgs at all. If we do not, we may need to propose new models of particle physics, or to change some of our parameters. It will be very, very interesting if we do not see Higgs.

What other questions can the LHC answer?

One of the big questions is about the nature of dark matter. Most of the universe is composed of mysterious dark matter. We don’t know what this dark matter is. We know that it has mass, that it exerts gravitational pull, and that it holds galaxies and clusters of galaxies together. Yet it does not contain any of the particles we have ever detected in experiments. Some scientists theorize that dark matter comes from a hidden symmetry within the universe — that every seen particle has a “supersymmetric” partner, which is like a heavier version of itself that is still invisible to us. It is possible that the LHC will confirm the existence of these supersymmetric particles, which will help us understand all the dark matter in our universe.

Another important question is why the universe is composed mostly of matter, and not of anti-matter. Physicists always assumed that matter and anti-matter were precise mirror images — identical, but with different charges. When matter and anti-matter meet they annihilate each other. The Big Bang would have created both matter and anti-matter. Then why is the universe filled with matter? The answer may be that there are slight differences in their properties that ultimately give matter a cosmic edge over anti-matter. The LHC will create both matter and anti-matter, allowing us to study whether, in fact, these differences in properties exist.

Are these collisions created by the LHC dangerous?

Absolutely not. The media has talked about the destructive potential of this experiment, sometimes referring to it as a “Doomsday Machine.” This coverage is completely unjustified. Earth is constantly bombarded by particles that are much more energetic than the particles that will be created at LHC, yet here we are. Everyone should safely sleep.

Are there practical applications of this research?

One never knows where scientific discovery will take us. These experiments will add to our understanding of the way the universe works, which will shape future discoveries and technologies. At the moment, I cannot foresee the direct practical application of these experiments. For me, it will simply be an incredible satisfaction to have new answers to some important and fascinating questions about our universe.

On the other hand, we can already see many indirect benefits of the LHC. The development of new detectors and more efficient particle acceleration is already being applied in medicine and technology. Also, the data collected by the LHC will be so vast that we’ve had to develop new methods of data storage and transfer. This has enormous worldwide applications. Until now, nobody had ever handled such large quantities of data!

What level of engineering went into the LHC?

It is a stunning feat. The LHC is the work of more than 10,000 engineers and scientists, hailing from every continent but Antarctica. Elements of the LHC were manufactured all over the world, in more than 20 different countries. It’s just an incredible initiative. If you lined up all of the wiring required for the LHC, you could travel 10 times the distance between the earth and the sun. At their peak speed, protons will travel .999999991 times the speed of light; they will rotate a 27 kilometer path more than 11,000 times every second. At the moment of their collision, these protons will have a charge of 7 trillion electron volts. The LHC will create a staggering 600 million collisions per second, yielding enough data to fill 100,000 DVDs every year. It is tremendously complicated, and very ambitious.

Abridged from an interview with Alison Benjamin in the OnCampus newspaper.