10 September 2008

The Machine

I'm fascinated by the scope and intent of the CERN experiments.

As a starting point:
The Standard Model
The Standard Model of particle physics explains how matter interacts with three of the four fundamental forces of nature: electromagnetism, the strong nuclear force (which binds the parts of an atom's nucleus together) and the weak nuclear force (which allows for the radioactive decay of particles). The model posits two classes of elementary particles: bosons, which mediate these forces, and fermions, which combine to make up the matter.

Where the Standard Model comes up short is when dealing with the fourth fundamental force, gravity. Gravity is so weak it can normally be discounted, but that's not possible in extreme cases such as the high-energy, small space predicted in the early moments of the Big Bang theory of the universe. In those moments, gravity would have been operating at levels comparable to the other forces.

Prior to the official start of the collider,CBCNews.ca spoke with Cliff Burgess, a physics and astronomy professor at McMaster University in Hamilton and associate member of the Waterloo, Ont.-based Perimeter Institute, about the LHC's mission, the potential risks and why physics should matter to the public.

Why are the LHC and its experiments so important to particle physicists?
More than anything, we have a good sense that we have to see something. It's not like we're looking and hoping to see something; seeing nothing is really not an option. You can't, for example, have just the particles we've discovered and no Higgs, because if you said "suppose there's nothing else," the whole theory breaks down at about the energies where the LHC would kick in. So something has to happen at that point; it's a question of what.

How difficult will it be to find?
That depends on what the Higgs is like. If it's complex like a proton, it will be much harder to figure out what's going on. When you collide two electrons together, it's much easier to understand what happens because these are elementary particles — they can't be broken down further — and they don't take part in the strong interactions that occur in nuclei. With the LHC, what's going to happen is it's going to be proton colliding with proton, and that's a whole bunch of junk. It's a mess figuring out what comes out of those collisions, partly because the whole structure of the proton isn't even now well understood. It's like throwing two garbage cans at one another and then trying to figure out in detail what was inside each garbage can.

What happens if the LHC doesn't find the Higgs, or discovers it doesn't exist at all?
That's actually the best-case scenario for people like me, because that means the theorists are all in business again. But the question for competing theories isn't so much whether the Higgs is there or not; it's whether it's a fundamental particle.

One of the concerns voiced by protesters is that the LHC collisions will create a black hole that will destroy the Earth, a concern the people at the European Organization for Nuclear Research have dismissed. Should anyone be worried?
If a black hole formed, we actually know a fair bit about what it would behave like. The first thing is, if you stuck a black hole in the middle of the Earth, the layperson's point of view is that it would be like a vacuum cleaner that sucks the Earth in. But that's not the right picture. If you took the sun and you replaced it with a black hole the same mass as the sun, the orbit of the Earth wouldn't change at all. We'd still orbit it — the force of gravity doesn't care whether it's a black hole or the sun, all it cares about is the mass. The big problem for us is it would be dark, but the gravity wouldn't change.

It's not so unlikely that the LHC could produce black holes, but it's almost certainly true that if it produces those black holes, they are going to evaporate very quickly.

Any black hole that you know about in astrophysics is much, much heavier than the ones being produced in the LHC. If the LHC produced black holes — which is uncertain — they might be a couple hundred times more heavy than a proton, but way less than fractions of a gram. And at that size limit, we expect them to evaporate extremely quickly through a process called Hawking radiation [which takes its name from physicist Stephen Hawking, who first proposed the theory in 1974]. It would almost certainly radiate into particles we know about like photons, and so it would look like a regular collision. The hard thing would be to actually know you had a black hole in there.

So there are several levels of argument where you kind of suspend what you think is likely to happen just for the sake of argument to grant the person the point that "maybe this could happen." But once you go through four or five levels of that, it's less and less worrisome.

Why should people care about this experiment and particle physics in general?
There are several ways to slice that question. The way it often comes is, Why should it be funded? Because on some level no one is going to be really offended if people spend their time thinking about this if it's not going to cost them anything. But if it's going to cost them a lot of money, then why should it be a priority for society?

The answer people normally give — and it's true — is particle physics is important to our understanding of the nature of the universe and the Big Bang, but there's another really good answer and no one ever gives it. The value of disciplines like particle physics and astrophysics is people.

Physicists are really in demand outside academia, and the reason they are is that the portable skills you get as a physicist are rare. You learn how to analyze problems from first principles, to translate that into mathematics, to solve the mathematics and then to translate it back into implications for the thing you are trying to solve. And that's really useful everywhere in the economy.

My students that go out into the workforce are bankers, insurance people, engineers and software people. These people are going into a very useful place in the economy, but they wouldn't have gone there directly. The reason they learn these skills is because particle physics is cool and you get to think about the universe as a whole, or you get to think about what matter is made of. And they are drawn by that in a way they wouldn't be drawn naturally into something like banking.

It's the old spin-off argument, but the way particle physicists would normally say it is in terms of materials and inventions made possible because of physics. But the real thing we make is people.

By that logic, wouldn't it be better to send the 2,000 physicists working on the LHC into the workforce?
That would be like killing the farmer and taking his crops. There would be some physicists and technicians that would go somewhere, but that's it, and once they leave you can lose the ability to do these things. What you want is the pipeline. The water is good, but you don't want to destroy the pipe to get the water the one time.

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