Satellite graphicThe application of Einstein’s theories of special and general relativity are central to the lives of all of us who rely on satellite navigation (GPS). Without application of these theories, positional accuracies would be measured in kilometres not centimetres. Very simply, Special Relativity tells us that the moving clocks on satellites seem to us to run slow and General Relativity tells us that the clocks situated ever farther from the surface of the Earth will appear to us to run fast. It is by measuring the difference in time given by different satellites that we can triangulate our position on Earth.