Where worlds collide: taking quantum weirdness into space

It is a meeting point, this vast expanse of near-nothingness hundreds of kilometers above the Earth's surface. Here, the planet's gravity is too weak for atmospheric gases to linger, but the absolute emptiness of outer space has not yet quite begun. Deep within satellites' sensors and electronic circuits, electrons and photons dance to the tune of the most fundamental theory of nature's workings: quantum theory. Its fuzzy uncertainties and instantaneous influences provide a peerless description of matter on the smallest scales but to predict how a satellite itself will move, people must call on a very different mathematical construction: the rigid, space-warping equations of Albert Einstein's theory of gravity, general relativity. Here, Hebden takes a look at quantum experiments into relativity's realm.