The weight of expectation

摘要

Newton devised his universal law of gravitation for planets, but does it work at small scales? A search for a deviation from the expected behaviour could provide the first evidence in support of string theory. Gravity, one may think, is a rather well understood subject. It has been more than 300 years since Isaac Newton determined that the magnitude of the gravitational force, F, between two bodies of masses M and m (separated by astronomical distances) depends on the inverse-square of the distance, r, between them: F= GMm/r~2. And we have recently passed the two-century mark since Henry Cavendish made his first measurement of the gravitational constant, G, which sets the fundamental strength of the interaction.