Tuesday, March 30, 2010

«Physics of the LHC»

The first 7 TeV collisions are now taking place in the Large Hadron Collider (LHC), breaking yet another record. They had achieved the 7 TeV energies earlier, but only now are they allowing the particle beams to cross and collide.

7 TeV is only half what the LHC was designed for. However, the LHC is basically its own prototype. It has been decided that the copper fail-safes between the superconducting magnets need to be redesigned before the LHC can reach the full 14 TeV power. The LHC will need to be shut down to perform these upgrades. For now they will run at half power until late 2011, at which time they will shut it down and upgrade it. It won't be scheduled to resume operation until 2013... So much for it being the 2012 doomsday device.

The LHC is 27km in circumference, and those hadrons (protons) in the beams are going around the ring 11,245.5 times a second. That's 99.999997828 percent the speed of light. There are 2 beams traveling in opposite directions.

Yet for all the power and speed of the LHC, nature bombards our atmosphere with far more energetic cosmic rays. Take the Oh-My-God particle for example. It slammed into the atmosphere over Utah with an energy of 3x10^20 electronvolts (equivalent to 300,000,000 TeV). That's why I'm not worried about black holes or anything else from the LHC eating Earth; if it were possible, nature would have already done it.

Special Relativity1

Some strange Special Relativity takes place between the beams. Despite moving at near light speeds in opposite directions, they're still not moving faster than the speed of light relative to each other.

The entire 27km circumference of the collider is only a little over a meter in length relative to a beam; this is known as length contraction. Yet from one beam's perspective, the other beam has to travel 202,500km to get around that same circumference once. (Funfact: a 703.5 TeV cosmic ray "sees" the entire Earth as 17 meters thick.)

There's also a strange time dilation that would cause a beam to "see" a clock at rest as running 7,500 times slower. Yet if an observer at rest were to see a clock traveling with the beam, it too, would appear to be running 7,500 times too slow. So from both perspectives, it would appear as though the other clock is the slow one. This effect is increased to 112,000,000 (that's millions) times if the two beams were to look at each other's clocks. (Funfact: a 703.5 TeV cosmic ray would have "seen" only 6,000 years2 pass in the 4.5 billion years the Earth has been here.)

Seriously... Science is stranger than fiction. Yet Special Relativity is tame compared to Quantum Mechanics. When the beams collide, the resulting debris particles are where the Quantum Mechanics aspect of the LHC begin... Then you've got stuff that exists in opposite states simultaneously (quantum states), can jump across an impenetrable barrier (quantum tunneling), and fundamental particles yet unknown to physics (the elusive Higgs boson).

1: These calculations were made for the full 14 TeV output of the LHC (7 TeV in each direction). However, because the energy required to accelerate something near the speed of light increases exponentially, the figures are not far off from the current half-power speeds.
2: If the young-earth proponents were riding a cosmic ray, they might have been right!


  1. "nature would have already did it"
    I think you mean 'done it' not 'did it.'

  2. They had an issue with a power supply, but after a couple hour delay they succeeded! The world's first 7 TeV collisions in a laboratory. I watched it live on their webcast.

    @ Vid: Really? Saying "done it" seems like redneck lingo to me.


  4. @ Vid: Yeah, ok... I'll change it.

    "Git 'er done!" - Larry the Cable Guy.


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