The beeping of the mobile phone awoke Prof. Hod Lipson in the middle of the night. "We found the equation!" his research student, Michael Schmidt, announced. The equation Schmidt was referring to has been known to every physicist since the 19th century. It describes the Law of Conservation of Energy - not exactly an earthshaking discovery. Nevertheless, as Prof. Lipson laid his head of disheveled hair back on the pillow, he did so with a smile.