by Markus Deserno One of the fundamental facts of statistical physics is that microscopic systems are subject to constant thermal fluctuations. They are fundamentally random, but still exhibit many regularities that permit us to learn a great deal about those systems. For instance, any individual quadratic degree of freedom of the form 12Kx2\frac{1}{2}Kx^2 has an expected value of the energy equal to half the thermal energy, or 12kBT\frac{1}{2}k_{\rm B}T. This so-called equipartition theorem in...