THERE are two kinds of theoretical physicists: those who use the correct equation for calculating distances in space-time, and those who don’t.

Obviously, I’m being a bit tongue in cheek here, but I’m serious when I say there is a real bifurcation. The two formulations of this equation for distance – what we call the metric – are equivalent and when used correctly will give the same answers for all calculations. But each group has reasons for believing that one is more natural than the other. Particle physicists tend to use one; relativists (people trained in general relativity) tend to use the other. I’m among the group of particle physicists who use …