Quantum physics, Einstein’s theory of relativity and atomic clocks that are accurate to one billionth of a second -- all of these are crucial in allowing your smartphone to pinpoint your precise location almost anywhere on Earth. It's called the Global Positioning System, or GPS. The GPS receiver in your smartphone uses trilateration — a more complex version of triangulation — to determine its position on Earth. In drawings, trilateration is often illustrated in 2-D using circles. But since GPS deals with satellites and Earth in the real 3-D world, spheres are a better representation of what’s actually happening.