In Conversation

Q&A with Don Lincoln
Author of The Quantum Frontier: The Large Hadron Collider

1. What is the Large Hadron Collider (LHC)?

The Large Hadron Collider is a new particle accelerator about to begin operations under the Franco-Swiss border. This accelerator is circular in shape with a circumference of fully 17 miles. It will accelerate two beams of protons, circulating in opposite directions, and collide them head-on in the center of four large particle detectors. The goal is to recreate the conditions of the early universe and study the moment of creation itself. It is much larger than the next-largest accelerator, which is the Fermilab Tevatron, which has a circumference of about 4 miles and is located about 40 miles west of Chicago.

2. What countries are involved in the building of and experiments for the LHC?

Countries from all continents except Antarctica are involved in building the LHC and the experiments based there. Over 7,000 scientists from 85 countries are currently collaborating to build this equipment. Currently there are 88 institutions from the US alone. The single largest US contributor is Fermilab, my home research institution.

3. Why do we want/need it? What can we learn from it?

The first of these two questions is a tricky one, the second one less so. The study of nature has fascinated mankind since time immemorial. Early shepherds stared at the clear midnight sky and wondered "How did we get here?" Questions like those continue to vex people today. The difference is we have now constructed enormous equipment that will provide us data that will help us definitively answer those questions.

The LHC will allow us to collide subatomic particles together with enough energy to recreate temperatures last seen in the universe under a trillionth of a second after the moment of creation (10^-13 seconds). Such temperatures have not been generally present for about 14 billion years. To be able to study the behavior of matter that far back in time goes a very long way towards answering "How did we get here?"

There are people who do not find interesting such fundamental questions. For them, only practical answers will suffice and we must point to such technologies as radiation therapy for cancer and the superconducting magnets for medical MRI scans. Both of these technologies are spin-offs from particle physics research. If these are not enough, we could also point to ultra fast electronics and trans-Atlantic communications. Indeed, the World Wide Web was born at CERN, the Swiss laboratory that hosts the Large Hadron Collider. Odds are that you are reading this article using a particle physics invention that initially was intended to facilitate communication between scientists spread across the globe.

4. How does it work?

The Large Hadron Collider uses a time-honored technique. If you want to concentrate a lot of energy in a single place and generate a lot of heat, bang two things together. Think about the spark seen when two hard rocks are smashed together. The LHC does much the same thing, except the colliding things are protons and not rocks.

The way we get protons to such high speed is to use very strong electric fields and magnets. The simplest way to experience an electric field is to rub a rubber balloon on your arm on a dry day. Then take the balloon and bring it near to your arm, without touching it. The sensation of your arm hairs being picked up comes from electric fields.

Now the electric fields used in a particle accelerator are much stronger than that, but the principle holds. These fields push the protons to higher speed. The large, characteristic, circular ring is just a series of magnets that bring the protons back around to the electric field for another push. It's not so terribly different than pushing someone on a swing. Each push can be gentle, but after several cycles, the person is flying very high and the proton is travelling near the speed of light.

5. Has anything like this been done before?

In many ways, particle accelerators are old hat. The technologies involved are about a hundred years old. Particle accelerators have existed in nearly every household in America since the 1950's in the form of television screens and computer monitors. While those old-style TVs accelerated particles with voltages of tens of thousands of volts, research accelerators are much stronger, with effective voltages of a trillion volts. In fact, the current champion of particle accelerators (the Tevatron at Fermilab) has achieved this record, trillion-volt energy.

When it is operating at full design, the LHC will be seven times more powerful and will be able to make a hundred times more collisions per second than the Tevatron. So the LHC is just a bigger version of accelerators with which we already have considerable familiarity.

On the other hand, seven times more energy and a hundred times higher collision rate is a big deal. The last time we explored such a new research frontier was over twenty five years ago. Just like Columbus' epic journey into the unknown west, particle physicists cannot know what they will find, only that there will be marvels and that the journey will be exciting.

6. What is the difference between electrons and quarks? What can we learn from them? Why are they so important?

An ordinary atom like the ones that make up everything we know in the universe, from you, to me, to ice cream and galaxies, consists of two components. There is the atomic nucleus and electrons which swirl around it at (relatively) great distances. Indeed, an atom can be imagined as something like a solar system with a nuclear sun and electron planets.

However, in the early years of the 20th century, physicists realized that the nucleus of the atom wasn't a simple little object like a billiard ball. The nucleus consisted of even smaller particles, called protons and neutrons. These protons and neutrons clump together like marbles that have been handled by a toddler with sticky fingers.

The journey towards the ultra-small didn't stop there. In the 1960s and 1970s it became clear that the protons and neutrons themselves were made up of yet even smaller objects called "quarks." (The name has no real meaning and comes from an inconsequential line from James Joyce's Finnegan's Wake.)

As of this writing, we know of no objects smaller than quarks. (Although it might be of interest to know that the search for such objects is my personal research project.) So to study the featureless quarks and electrons is a study of the ultimate building blocks of matter. With the right kinds of quarks and electrons and an appropriate cookbook, everything we've ever seen in the universe can be assembled. Everything. Isn't learning all there is to know about them a worthwhile endeavor?

7. Are you running any experiments with the LHC? What things do you want to learn from the LHC?

Oh yes, there will be countless experiments performed by scientists working at the LHC. There are four extremely large particle detectors situated around the seventeen mile circumference of the LHC. These detectors are called CMS, ATLAS, ALICE, and LHCb. Both CMS and ATLAS are designed to study the very most violent collisions. It is from these experiments that most expect the early and exciting discoveries, some which may require that we scientists totally revamp our understanding of the universe. It's safe to say that these are extraordinarily exciting times.

The other two experiments are designed to study different phenomena in great detail. LHCb is designed to try to explain why the universe is composed entirely of matter, when we always manufacture equal amounts of matter and antimatter in our experiments. ALICE has a quite different mission. It is intended to study the behavior of subatomic matter when it is heated in (relatively) large volumes. It will achieve this goal by colliding beams of not protons, but rather the nuclei of lead atoms from which the electrons have been entirely stripped.

One of the most frustrating questions I encounter in my frequent public lectures is "What are you going to find?" And, of course, the answer is "I don't know." This is, after all, research. We can guess at what we might find, but of course it's possible that what we'll encounter might be something totally unexpected. Just ask Columbus how that trade route to the Indies worked out.

However, we can talk about what we are looking for. We are looking for the Higgs boson, also called the God Particle in Leon Lederman's book of the same name. This particle, if it exists, is the source of subatomic particle mass. We also search for objects smaller than the quarks and leptons that are the smallest objects we've discovered. This is of particular interest to me. There will be thousands of studies, some studying things we know in an entirely different energy regime and some simply looking for something entirely new.

8. What other experiments is CERN running? What does CERN want to find out?

CERN, like any large laboratory, has many things on which it works. While the LHC is currently consuming a lot of the laboratory's resources, scientists there are involved in understanding neutrinos: ghostly particles that can penetrate the entire Earth without interacting. They are also very interested in the search for dark matter, which turns out to be about 5-6 times more prevalent than the "ordinary" matter that makes up everything in the universe that we have ever seen. Other scientists try to understand dark energy, which makes up fully 70% of the universe. (Contrast this with dark matter's 25% and regular matter's mere 5%.) Scientists at CERN and other large laboratories (like my own Fermilab) are asking big questions, hoping for big answers.

9. When the LHC was activated last fall, the media talked about the possibility of a black hole. Is this possible? Is there anything we should be worried about?

No. Not one tiny bit.

It is impossible that the LHC could do something that is dangerous to the existence of the laboratory, Switzerland, Europe, the Earth, and mankind. Absolutely and totally, 100% impossible. Full stop.

However some people have been unnecessarily worried by fear mongers and consequently it is very worthwhile to understand why we scientists are so certain that it is safe. Before we do, I should note that particle physicists are grateful that the question was raised and that they had the opportunity to study the issue and set the public's mind at ease. Scientists are citizens too, with children to raise and eventual grandchildren to bounce on their knees. It is entirely fair to ask them to demonstrate the safety of their apparatus. After all, this is something mankind has never done before.

However, for all the cleverness of mankind and the happiness of scientists that we can study things we've never studied, Mother Nature is far more clever and powerful. Each and every second the Earth is constantly bombarded by so-called "cosmic rays." Cosmic rays are protons from outer space that the universe itself has accelerated in various ways and flung across the vast cosmos. Some of those cosmic rays hit the atmosphere of the Earth. Because the atmosphere of the Earth is made of atoms, which are in turn made of protons, these cosmic ray collisions are protons hitting protons, just like the LHC.

Now most cosmic rays are relatively low energy, a pea shooter to the rifle of the LHC. However the universe is a big place and some cosmic rays have huge energy. . . energy of the sort about which LHC scientists can only dream. These cosmic rays are cannons to the piddly rifle of the LHC. One can easily prove that this has been going on since the Earth began, about four and a half billion years ago. And, when one does the calculation, one finds out that the LHC would have to run for one hundred thousand years to generate as many collisions of this sort of energy as regular cosmic rays have experienced hitting the Earth alone. If one includes bigger objects, like the Sun, you would need to run the LHC for billions of years to make as many collisions. And the energy of these collisions are even higher than the LHC can do.

If the Earth and the Sun have survived this onslaught, the LHC cannot do anything that will endanger mankind. Sleep well at night unless, like me, the excitement of the new discoveries keeps you awake and you have to count quarks to go to sleep.

10. I saw Angels and Demons and the LHC plays a role. Is that possible?

Well yes and no. In this movie, a scientist isolates a quarter gram of antimatter which is claimed to be an explosive with nearly the destructive capacity of the bomb that destroyed Hiroshima. The antimatter was isolated at CERN and the bomb was placed in the Vatican.

So there are truths, half-truths, and falsehoods in the book and movie. First, antimatter is real and a gram of antimatter could be used to fashion a bomb of Hiroshima power. Further, CERN is a place where antimatter can be made. (Although its sister laboratory of Fermilab is the better laboratory of the two to make antimatter.)

So the physics of the movie (and especially the book) is plausible. However, the engineering of the movie is totally fictitious. Making antimatter is hard. My colleagues at Fermilab have worked exceedingly hard to make as much antimatter as possible. We run our accelerators 24 hours a day, for years on end, to make antimatter by converting pure energy to antimatter. However, after nearly thirty years of effort, we have made about as much antimatter as one might need to heat up an urn of coffee suitable for a dinner party of twenty people from room temperature to something drinkable. In order to make the amounts of antimatter discussed in Angels and Demons, Fermilab scientists would take millions of years using modern techniques. Given that there are tens of thousands of nuclear weapons and even hydrogen bombs with a thousand more times destructive potential than the Angels and Demons bomb, it is entirely clear that there will likely never be an antimatter bomb.

So the physics is good, but for practical economic and engineering reasons, the science of Angels and Demons is pure fiction.