Optimum Copyright period decided by maths!

An anonymous reader writes: So how long SHOULD a copyright be valid for? There are as many opinions here as there are humans. But a Cambridge student has stepped into the discussion with a dispassionately calculated estimate of the optimal period a copyright should be granted for. Here is ArsTechnica's take: http://arstechnica.com/news.ars/post/20070712-rese arch-optimal-copyright-term-is-14-years.html, and here is the original paper for all you maths dudes out there: http://www.rufuspollock.org/economics/papers/optim al_copyright.pdf