Einstein’s theories are open to a variety of tests. In the case of special relativity, for instance, it is possible to put very accurate atomic clocks on board commercial airliners as they fly around the world and check whether they show the differences in flight time that the theory predicts their high-speed journeys will cause. They do. In the case of general relativity, one classic test involves the observation of starlight passing close to the edge of the Sun (this can be seen during a total eclipse).

According to the theory the paths of such rays should be bent due to the space-time distortion produced by the Sun. It is. A more everyday check on the correctness of general relativity is provided by the operation of the Global Positioning System. The GPS allows anyone with a suitable receiver to pinpoint their location on Earth by analysing the differences in radio signals received from a network of orbiting satellites. The accuracy of the system is such that relativistic effects have to be taken into account in order for the analysis to provide.