Let the Large Hadrons Collide!

There was much to-do leading up to the Large Hadron Collider's first circulating beam today. Many questions were asked of me, as a physics teacher:

Q: What's a hadron?
A: A hadron is anything made of quarks (and/or anti-quarks), like the protons and lead ions that will be colliding in the LHC.

Q: Is the world coming to an end because of the LHC?
A: Not likely. Collisions of this energy occur often enough in cosmic rays, and we haven't seen the Earth (or any other planet for that matter) come to an end yet. It might be that Earth-ending events are possible, but extremely rare, so we just haven't seen them occur with cosmic rays ever in the history of the earth - and we just might get really unlucky when hadrons collide in the LHC. Then again, we might just get really unlucky next time a cosmic ray hits earth.

Q: We survived the startup of the LHC, are we safe now?
A: Just as safe as you were before. The LHC startup today was just the startup of the beam circulating, there haven't been any collisions yet. So far we have a NASCAR race running under the caution flag - all the protons are going the same direction around the track with the same speed - so we don't see any collisions. Once the beam is stabilized - probably in the next few weeks - they will start colliding beams. Imagine a NASCAR race where half the cars are going the opposite way around the track - big time collisions! Even then, they will only be colliding protons at their current energy of 450 GeV. Eventually, the energy of the protons will be increased by a factor of 10+, to 5 TeV, where really interesting stuff is likely to happen. (The accelerator's magnets are capable of keeping protons with as much as 7 TeV of energy circulating around, so expect to see the energy increase to that eventually.)

Q: What interesting stuff is likely to happen?
A: There are particles that have never been observed, but are predicted by various theories of particle physics. Physicists are hoping that the LHC will give evidence about their existence. For example, the Standard Model of Particle Physics predicts that the only reason any particles have mass is because of a particle called the Higgs; the LHC may find evidence of it. Supersymmetry theory predicts that all the particles we know have supersymmetric partners that are very heavy; the LHC may find evidence of them.

Q: Is 5 TeV really a lot?
A: Yes and no. An eV (or electron-volt) is the amount of energy that one electron gets from being accelerated across one volt. 5 TeV is 5 trillion times as big. That sounds like a alot, until you compare it to some everyday energies. If you run a standard AAA battery dead, you have used approximately 40 billion TeV. So 5 TeV is not a lot of energy, but...
a) It's not a lot of energy for the unimaginably many electrons in a battery to have, but it is a lot of energy for one tiny particle to have. In order for one single proton to have 5 TeV of energy, it must be going very, very, very fast - very, very, very close to the speed of light. It's speed differs from the speed of light by only about 1 millionth of a percent! (PHYS 301 students - do that calculation - on the double!)
b) Each single proton in the LHC beam will have 5 TeV of energy, but they will be accelerating about a quadrillion (10¹⁵) protons each day. That's a total energy of about 1GJ, or about 100,000 AAA-batteries, or one speeding train!

Q: Why do we need so much energy?
A: Matter can be converted to other forms of energy - that's how nuclear power plants produce energy to power your electric appliances. Other forms of energy can also be converted into mass. The more massive the particle you want to create, the more energy you need. And it can't be energy spread out like a battery or a train, it has to be concentrated into a single collision of two particles, like the protons in the LHC.

Q: What if I want to know more?
A: You can ask me, or check out this page from CERN which gives some quick facts and figures, then links you to a brochure full of much more info. I also like the US/LHC blog, from whence I stole the image above. They have some amusing tongue-in-cheek posts about destroying the world - good that they can laugh at themselves. For up-to-the-minute reporting, we also have our own correspondent on-site. '03 alum Karen Andeen is currently at CERN, and reports that there were a lot of cameras around to record the end of the world (for posterity?)