Spooky Timing: Quantum-linked photons coordinate clock ticks

Check out the closest half-dozen timepieces, and they’re almost certain to disagree by at least a few seconds. That variation doesn’t cut it for global data networks or fleets of satellites, where even microsecond differences among clocks can wreak havoc. Thanks to sophisticated computations, high-speed electronics, and in some cases relativity theory, the far-flung clocks of those systems can tick within just a few nanoseconds of each other, despite separations of thousands of kilometers.