11/4/2010

The Large Hadron Collider

Filed under: — Bravus @ 9:49 am

(wrote this for another purpose elsewhere, but since I’ve alluded to the LHC here a couple of times here I thought I’d share)

I think there’s a lot of nonsense being talked about the LHC, what it is and what it does. Talk of ‘God particles’ and ‘mini-big bangs’ is journalistic license, or scientists doing a bad job of trying to popularise.

The Large Hadron Collider is simply the biggest and most powerful particle accelerator ever built. A lot has been learned about the world of subatomic particles in just the last century or less: the neutron was not even discovered until 1932.

One of my friends said ‘they used to do this stuff a lot more cheaply’. The less interesting part of the explanation is just inflation, the more interesting part is that the more deeply you probe the mysteries of the subatomic world, the more energy you need: and the LHC provides immense energies.

Basically, the LHC uses pulsed magnetic fields (generated by massive superconducting electromagnets, kept close to absolute zero by liquid helium), to accelerate protons (the ‘large hadrons’ of the title) to very close to the speed of light, and then collide them with other protons that have been spinning around the circle the other way at the same speed. (It can also do larger metal ions in a separate set of experiments.)

karl talked above about driving at ‘a fraction of the speed of light’, and of course he was. But these protons are travelling at something like 99.99% of the speed of light. According to Einstein’s theory of Special Relativity, under those circumstances the mass of the particles increases, in this case to over 7000 times the rest mass of a proton. They then collide with equally heavy protons going the same speed in the opposite direction, releasing immense amounts of energy.

The ‘mini-Big Bangs’ thing is a misnomer, but the point being made is that one of the things the LHC is doing is creating conditions like those believed (by some, heh!) to have existed a tiny fraction of a second *after* the Big Bang. The four forces we know in our universe now (strong and weak nuclear, electromagnetic and gravitational) did not exist in the very first picoseconds (actually even earlier than that) of the Big Bang, but were created at different times during the process… and the LHC is intended to allow us to better understand how those forces arise.

In particular, the Standard Model of subatomic particles struggles to explain something fairly simple: why do objects have mass? (And therefore gravitational attraction.) One theoretical prediction is the existence of a heavy particle called the Higgs boson. This particle would explain the existence of mass and gravity… but not everyone believes it exists. It can be observed (if it does exist), but only under very extreme conditions… like those offered by the LHC.

If the Higgs boson is found, the Standard Model will be supported by the evidence, and we’ll move on to explore it further. If it’s not, that model will be overturned or modified, and the search will go on.

It’s a bit hard to imagine on a human scale: protons weigh on the order of 10-27 kg.

Let me put it this way: if karl was driving at the same fraction (99.99%) of the speed of light, he would be doing 670 million miles per hour. His 1 ton car would have a mass of 7000 tons: 35 Boeing 747 jets.

Now imagine that crashing into another one going the same speed in the opposite direction…

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