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Particle Fever

For physics neophytes, Mark Levinson’s documentary Particle Fever is an accessible and entertaining primer on the make-up of the universe. The film not only gives viewers an understanding of complex ideas in theoretical physics, such as why the energy of the elementary Higgs boson matters and why it was dubbed the “God particle,” but it also conveys the everyday stakes involved in such questions.

The film follows the launch of the Large Hadron Collider, the world’s biggest and most expensive “atom smasher” on the planet, from its dramatic takeoff in 2007 through to its climactic discoveries in 2012. And while the film is filled with fun facts about particle physics and philosophical questions about the Big Bang, the movie only brushes the tip of the iceberg. We asked one of the film’s producers, David Kaplan, an assistant professor in physics and astronomy at Johns Hopkins University, about what they had to simplify and excise about the LHC project and their scientific work, from dark matter to the concept of naturalness.

Sloan Science and Film: Were there areas of physics that you had to overly simplify or leave out of the film entirely?

David Kaplan: There was a lot of other physics happening outside of the LHC. And we had a whole sequence about attempts to discover dark matter. What you learn is that not only that there are other theories, but also there are lots of other experiments that people are doing all over the world. They are distinct in the way they look for dark matter, which are these new particles or types of particles that we believe fill the universe. Something like 80% of the matter in the universe is this stuff, which is not made of atoms and it’s not made of anything we have seen before. And there are plenty of theories about what it might be.

During the one year the LHC was shut down for repairs, there was a lot of excitement in the world of dark matter, because there were some signals that they had discovered it. This culminated in a big announcement. But when they finally presented their results, they were ambiguous, at best, but more likely, they didn’t see anything. So people were upset. And we saw the characters going through that. So we had this dramatic tension, but it was also showing the LHC was not the only game in town. But in the practical storytelling it was too much: it was another physics concept to absorb.

SSF: Were there other particles that were discovered that the film doesn’t mention?

DK: There were no other particles that were discovered at the LHC. There were hints of things. But at the Tevatron, [a particle accelerator in Illinois] which was running into 2011, there was one announcement of a discovery of a new particle, but those particles were made of quarks; they’re not fundamental particles. They are new bound states, collections of quarks, but they don’t add to the list of the fundamental particles that were at the beginning of the universe.

SSF: What about the divide in the film between theories of the multiverse as opposed to supersymmetry. Is it that cut and dry?

DK: It is not cut and dry. But they are perfect representations of the dichotomy that was occurring in physics at the time. If there’s a simpler or more unified theory of everything, supersymmetry had been the leading theory for what that is. There are a number of other theories, but supersymmetry had the most indirect success. It was popular, and it became a symbol of that type of physics. Does supersymmetry predict that the Higgs is 115GeV [a measure of energy]? No, but what it does do, in the simplistic class of supersymmetry theories, is say the Higgs is very light.
On the other hand, the multiverse is an even more vague thing. It’s representative of another way of thinking. The multiverse represents a possibility of how the numbers that we see—the masses of particles and the strengths of forces—could be a red herring. What if the numbers in the theory are random? And why would they be random? Maybe there are many universes, or parts of the universe, where the laws of physics are different, and it’s randomized, and we happen to be in a universe, which is nice for life, and therefore that’s where the observer is, but we can’t see the other universes. That’s the multiverse.

It’s not a specific theory; it’s a framework for what the larger space-time is, and the fact that there may be other laws of physics in other places. And as we push harder on those laws, we might get to a point where you can’t discover anything beyond that point, because you don’t have access to the full information. You’re just looking at a set of random numbers. What that practically means for the LHC is what if the Higgs is the last particle we ever see? What if the energy scale of the Higgs came out of nowhere, and was a total random accident? What if we are biased by the part of the multiverse that we’re in?

SSF: I was looking at diagrams of the Standard Model. But I didn’t see any that looked like the image in the film, with the Higgs boson in the center. Is there a reason for that?

DK: I always hated those diagrams. I always thought they were useless. People drawing them were doing something practical: they wanted to match the Mendeleev's table of chemistry, which is a rectangular grid. But in our case, it contains almost no information. And there’s a better way to do it. So I had been working with many ways to re-display the Standard Model. But everything I came up with was quite complicated. You couldn’t write it on a page: It was a 3-D chart. But Walter Murch, our editor, said he would come up with something, and he came back with this structure, and it doesn’t contain any more or less information than those other grids, but it’s more aesthetically pleasing. And it puts the Higgs in the center. And one thing it does in a clear way is that it distinguishes particles of different spin. Higgs has no internal spin, and the next layer is the spin 1 and the outer layer is the spin one-half. So everything in the inner two layers are bosons, and the outer layer we call fermions.

SSF: What do physicists think of Murch’s chart?

DK: They love it because it looks nice. They’re starting to use it.

SSF: Given that you are aiming for a general audience, is there anything else that you had to leave out of the film that you wish you could have kept in?

DK: There is one more thing, which is why we think the Higgs should come with supersymmetry: It’s called “naturalness.” It turns out if the Higgs is much heavier, it screws up the interactions of fundamental particles, so that our universe wouldn’t have chemistry, which would not allow for planets or people to exist. So there must be something out there that keeps things where they are. The concept is called naturalness, which predicts that the particle should be acting the way it should. And for me, there was a whole other story about the people who came up with the concept of naturalness in the 1970s. They decided that there was something wrong with the Higgs theory, and there needed to be other physics associated with the theory. There was a guy named Ken Wilson, a professor at Cornell. I had planned to interview him, and then interview the people who he influenced, so you could trace back the thought that there was something beyond the Higgs. They all trained our generation of physicists. If the multiverse is true, and it effects the Higgs in this way and there’s nothing else there, that incorrect theory would come from this one person. He’s one of the most impressive figures in theoretical physics. He didn’t even write a paper about it, but the statement influenced a lot of people.

SSF: Will there be a sequel to Particle Fever once the LHC starts up again in 2015? Is there anything you anticipate?

DK: The amazing thing about when the LHC was first turned on was the sense that something would be seen, and it would be the Higgs or something instead of the Higgs. That guarantee gave me confidence that this film should be made. But this is not true of the higher energy LHC. We don’t have any confidence that there will be any specific theory that’s breaking down right at that energy, where you know something will come up. We believe there’s dark matter. I think there’s real evidence for its existence, but what it is and what its properties are is unknown. Not seeing it at the LHC reboot doesn’t mean it’s not there. It just means that it doesn’t have those unique properties. Before, it was a unique time. I don’t know another moment in my lifetime where there was an experiment where a result would come up and it would have such a dramatic impact on the field.