I’ve just been at a really interesting cafe scientifique in Brighton where Philip ‘Critical Mass’ Ball talked about using physics to model the behavior of people en mass. When modeling people as particles you can create surprisingly realistic simulations of real behavior in corridors, traffic jams and panics. As fascinating as this is, I only think this I’d useful on situations where there is little historical evidence to rely on and where the cost of change is high. In the case of parks it is much better to ship a park in beta without any paths and then close the park in November to pave the cow paths than it is to model the park up front and hope that your model bears some resemblance to reality. Physics has invented models of reality just as reality has invented methods of measurement that don’t require modeling. Jeremy Keith is Philip Ball’s nemesis, whatever he may say.