An invisible hand?

“ASSUME nothing” is a good motto in science. Even the humble pendulum may spring a surprise on you. In 1954 Maurice Allais, a French economist who would go on to win, in 1988, the Nobel prize in his subject, decided to observe and record the movements of a pendulum over a period of 30 days. Coincidentally, one of his observations took place during a solar eclipse. When the moon passed in front of the sun, the pendulum unexpectedly started moving a bit faster than it should have done.

Since that first observation, the “Allais effect”, as it is now called, has confounded physicists. If the effect is real, it could indicate a hitherto unperceived flaw in General Relativity—the current explanation of how gravity works.