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Contemplating future plans for particle colliders

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Caltech physicist Barry Barish is the director of the global design effort for the International Linear Collider, which is currently in the planning stages. If built, the ILC would smash together electrons and their antimatter counterparts, positrons, at nearly the speed of light. The ILC would complement the Large Hadron Collider, a European proton collider that is the world’s most powerful but has had technical problems that will prevent it from operating at full power until 2013. That gives the world’s second most powerful collider, the Tevatron at the Fermi National Accelerator Laboratory in Batavia, Ill., a slim chance to be first to find evidence for the long-sought Higgs boson, which has been proposed as the particle responsible for providing other particles with mass. Following a presentation on February 22 in San Diego at the American Association for the Advancement of Science’s annual meeting, Barish answered questions from the audience and news media about the future of particle physics. Science News Deputy Managing Editor Elizabeth Quill compiled some of his comments.

Do physicists think that the Large Hadron Collider’s findings will be the end of particle physics?
There is a tendency we have among ourselves to use colorful language — quarks, neutrinos and all these things — but also maybe to speak in hyperbole.... [The end] is nowhere near because we barely can formulate the right questions to ask yet about the early universe…. We have a popular theory called string theory, and string theory doesn’t predict very much at this stage … yet people go around calling it the theory of everything.

There is kind of some narrow line between being humble enough to say you don’t understand everything about nature and you are starting to ask the questions, and radiating your enthusiasm for the fantastic things you are doing. Somehow we don’t have exactly the right balance.

Will results from the LHC provide confirmation for any existing theories?
I think in some areas we are going to be completely surprised because the theories aren’t really very deep. So the fact that we have some theory —  which I would call a model, not a theory — means we are able to make predictions. And that is very good for experimentalists, because it allows us to design detectors that we can test against somebody’s ideas….

One of the biggest surprises may come, in my mind, in what’s publicized as the Higgs boson.… We have a theory of elementary particles, which works pretty well, but [its particles are] massless and we put this [the Higgs boson] in by hand. It’s one guy’s idea, and life is probably different than that.

Once the LHC is running at top energy, will the world need the International Linear Collider?
If you look at how particle physics has been done over the last decades, it’s been a combination of two complementary techniques — colliding hadrons and colliding electrons.... If we project into the future what we think the science is going to be like at the Large Hadron Collider, it is going to again be true that you are going to want an electron machine to complement and to fully realize that.

The caveat, of course, is that ... you don’t lose that much by being patient — that one should see that the science that comes out of the LHC has some semblance of the hype that we have given it.

What’s a realistic timescale for construction of the ILC?
Well, it is going to take three to five years to learn enough from the LHC to warrant making the kind of investment [that ILC requires]. And then it will take 10 years to build it. That is where I came out with 2025 as the time­scale.… To make sure that we can do it even on that timescale, we are investing significantly in the technology to be able to make a large linear collider.

Given that the LHC is gearing up so slowly, might Fermilab find the Higgs boson first?
Yes, they are going to run for another year or so.... Fermilab is our best bet, for the time being, to see the Higgs.

Will there be even more powerful accelerators in the future, or are physicists reaching a limit on how fast they can make particles go?

The limitation in accelerators themselves comes from a couple things, but one of the main limitations is materials…. It has been demonstrated that if you can get rid of the materials, you can make much higher gradients to accelerate particles to higher energy. And this can be done with plasmas or lasers…. The problem is we don’t know how to make a laser or a plasma accelerator that has all the elements that you need to focus particles to efficiently do all that kind of stuff.

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