Who Knows: Professor Kannan Jagannathan on the Large Hadron Collider
Built by the European Organization for Nuclear Research (CERN) near Geneva, Switzerland, and opening officially in October 2008, the Large Hadron Collider (LHC) is a 17-mile long underground particle accelerator – the largest such machine to date. Amid concerns about its high price tag and possibly world-ending ramifications, Samuel Masinter ’04 sat down with Bruce B. Benson ’43 Professor of Physics Kannan “Jagu” Jagannathan to straighten out misconceptions about dragons, cosmic rays and the fundamental quest of science.
Bruce B. Benson ’43 Professor of Physics Kannan “Jagu” Jagannathan
KJ: It’s only $8 billion; that’s not much. It’s what – five days of war in Iraq? Well, there is the Standard Model of particle physics which was essentially completed around 1973. From the beginning, nobody thought the Standard Model was the end of the story. People expected that at some level, there are phenomena that require theoretical structures that go beyond the standard model. So the main motivation for building the LHC is to have access to realms of energy and short distances that would reveal where the standard model breaks down. It’s a very fundamental quest, at least for people in this business.
SM: Are they looking for anything in specific?
KJ: One thing they’re looking for is the Higgs boson [particle]. The Higgs boson, at least in its minimal version, is part of the standard model. So even for the standard model’s predictions to succeed as they do, one needs to affirm experimentally that there is this Higgs boson particle. But in fact, if one goes beyond the standard model, one expects that there may be more particles that will tell us why the standard model needs completion. That’s really the central quest.
SM: How do we know the Higgs boson exists if no one has ever seen it?
KJ: Different particles have different masses – electrons have a certain mass and protons are made of quarks that have their masses. The Higgs boson is the theoretical entity that allows electrons and quarks to have mass without breaking the fundamental symmetry in the Standard Model. If you need particles to have masses, you need the Higgs boson. So it’s as fundamental as “Why is there mass?”
SM: How will the LHC allow scientists to search for the Higgs boson and other new particles?
KJ: The accelerator speeds up particles and antiparticles using magnets along a track. In this case, the proton and the anti-proton are accelerated in opposite directions and made to hit each other in a tiny space at enormously high energy. The collision creates heavier, newer particles where all of the energy that went into the collision can be converted into mass, along the lines of E=MC^2.
The LHC will reach energies that are about 14 trillion electron volts. That’s about three to 10 times more than existing accelerators. There are theoretical bounds on the possible masses of the Higgs boson itself, and we are approaching that narrow window.
SM: What if the Higgs boson doesn’t show up?
KJ: If the Higgs boson does not show up in these collisions, massive as it is, then…it’s even more puzzling. If the Standard Model is fundamentally sound, the Higgs boson had better show up when the machine fires up.
SM: Some are concerned that creating this level of energy could create a doomsday scenario.
KJ: There’s a lawsuit filed against the American entities contributing money and resources to the LHC. The fear is, according to the people who filed the lawsuit, that when you create these energies that have never been created before, there’s the danger that a tiny black hole might form. Black holes, being what they are, might accrete mass—an exponential process that will eventually swallow up the earth. That’s one worry, I guess. There are other more technical worries like vacuum bubbles and strangelets, but they’re all of a similar doomsday scenario.
SM: Is this a valid concern?
KJ: Well, there’s a common saying among quantum physicists: if something is not forbidden, it is compulsory. We only calculate probabilities of events. So, unless there are symmetry or conservation law reasons to say that some process is impossible or forbidden, then the probability of that process occurring is typically non-zero. In an infinite universe, even things of low probability must occur (actually infinitely often).
Of course, non-zero can be quite a range – it can go from one in a billion to one in a billion billion, and so on. If you think of any thing that might happen, like Tony Marx opening his kitchen faucet tomorrow and a dragon coming out and biting him, you can calculate the probability of that process. It is probably non-zero because it’s not forbidden by any known conservation laws. But we wouldn’t say, therefore, that Tony Marx should not go near his kitchen faucet tomorrow.
Two groups of independent experts have looked in detail at the risks posed by the LHC and have concluded that there is no reasonable risk (of the exotic kind). Moreover, experience with cosmic ray events lends some empirical support to the assessment that the risk is well below the threshold of rational concern. As the inimitable Ashton Kutcher says in Dude, Where’s My Car?, “I don’t want to go down in history as the dude who destroyed the Universe”.
SM: As a theoretical physicist, do you have any reservations about the operation of the LHC?
KJ: Well, no, I don’t think so. There’s always a question, compared to certain pressing needs, whether this is the way that money should be spent. But that’s always an unfair question when it comes to matters of cultural investment. This is part of a cultural quest to understand the universe. Could $8 billion go into cancer research? Maybe. But it’s not a zero-sum game that pits art and music and science against the practical needs of humanity. Was it Lear who says, “Our basest beggars in their poorest things are superfluous”?
SM: Is there a point at which the search for knowledge becomes so expensive that we have a moral obligation to stop searching?
KJ: Yes. I don’t know about a moral point, but politically, we will stop. This has happened before. The most famous example is the Superconducting Supercollider which was not only proposed but funded. The Superconducing Supercollider was going to be situated in Texas; a huge hole was dug in the ground, work was started, and at some point, Congress decided that it was not worth it and [the project] was stopped. I don’t think this is a fundamentally moral question – it’s a question of judgments about allocations of resources at a particular moment, the magnitude of the resources, and so on.
SM: Do you think the LHC will answer more questions than it will raise?
KJ: Actually, we hope it will raise more questions than it will answer – that is part of science. We don’t really expect this to be the end of the road or that there will be nothing more to find. I hope, and I imagine most physicists hope, that you find some answers, and you also find some questions, and you go on.