Friday 1 October 2010

Understanding physics, or not.

I feel as though I understand this. That is to say, I can see how these stories might be explaining things.

The concept of quarks and gluons are in some sense 'reasonable' and I can imagine relativistic calculations on their energies, and cross-sections derived from the wave-functions of quantum mechanics. Of course I can't do those calculations, but I believe they can be done and I can see that in doing them they would explain the measurements (and thereby 'carry' some sort of understanding of the world).

I say this, because it is in contrast to anything I've read about string theory. I have just never got any sort of grip on what string theory is doing. I don't know whether this says something about me - perhaps to do with when I did my physics degree - or about string theory, or about the people who write about string theory, or about the nature of understanding.

It is probably about all of those thing, but it bothers me.

Amplify’d from

Quarks, gluons and jets

The LHC paper I've been working on for the past few months is finally out. It shows quarks and gluons doing what they should do, and I love it

When we collide protons, we really care most about the collisions between the proton's constituents - quarks or gluons. Unfortunately the quarks and gluons only carry a fraction of the energy of the proton, and we have no way of choosing how much. If the fraction was a half, for example, then we would have jets with 1750 gigaelectronvolts (GeV) of energy (half of 3.5 TeV). But most of the quarks and gluons carry much smaller fractions.

To have a real measurement of this, and show that the theory prediction (quantum chromodynamics, labelled QCD on the plot) agrees with the data, is a real achievement. It directly involved dozens of people, and less directly hundreds. One key component is the energy calibration which I described here.


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