Posted by caraher on September 7, 2007, at 19:00:57
In reply to I have good news...and some more good news., posted by Michael83 on September 6, 2007, at 19:03:22
Donning my physicist hat...
> 2. Large Hadron Collider, Switzerland. Scientists are taking atoms, accelerating them at the 99.5% the speed of light in opposite directions and crashing them together with literally the force of a freight train, with that force confined the size of an atom (mind boggling, I know). It's been done before, many times, but they keep doing it bigger and bigger.
Two nit picks... first, they're going faster than 99.5% of the speed of light. The LHC web site says the value is 99.9997828% of the speed of light. It takes a lot of energy to inch your way higher in speed as you approach the speed of light - those three extra nines are hard to buy! It's a nit-pick in terms of speed, but a huge deal in terms of energy (which is the important parameter).
Second... "literally the force of a freight train" doesn't make a lot sense to me. I'm guessing that you heard an expression like that from someone who took the momentum transfer involved and divided by the duration of the proton-proton collisions. But force is not a very useful concept in understanding these kinds of events. And it's a very misleading way to talk about the energies and momenta involved.
It's like in my field, where laser scientists talk about short pulses with peak powers comparable to the entire electrical generating capacity of the US. The total energy in a given pulse is quite modest in absolute terms, maybe comparable to the energy it takes to keep a light bulb on for a few seconds. It's just that the energy is delivered over such a tiny period of time that when you divide the energy by the time you get a huge number.
The kinetic energy of each proton at LHC is 7 TeV, which works out to one microjoule. Now that's a lot of energy for one particle as tiny as a proton... but for comparison, if I walk with a speed of 1 m/s (just over 2 MPH, a very casual stroll) my kinetic energy would be 50 joules - greater by a factor of 50 million!
Still, there are LOTS of protons in the ring! According to the wikipedia article on LHC, the energy in the circulating protons is 725 MJ. Now that I look up typical freight train masses, a small freight train traveling at a typical top speed has about that amount of kinetic energy. So mystery (for me) solved; that's probably what they meant. That energy is not all in a single particle or released in one collision; rather, it's spread throughout the collider.
poster:caraher
thread:781229
URL: http://www.dr-bob.org/babble/social/20070827/msgs/781491.html