Who controls time around the world?
Who coordinates the time that governs the world’s time zones?
The international coordination of time is controlled by the International Earth Rotation and Reference Systems Service, IERS.
IERS is responsible for keeping an eye on Earth’s accurate rotation, and adds ‘leap seconds’ to keep time synchronised with Earth’s rotation.
The rotation can vary slightly in connection with severe earthquakes and other events. The quake that took place on 11 March 2011 in Japan led to IERS declaring the earth day to be about 1.8 microseconds shorter.
Physically, the indication of time throughout the world is governed by atomic clocks, which use the fact that atoms have a natural resonance frequency that is always the same for a specific type of atom. By producing an electromagnetic field that oscillates in time with the atoms’ frequency, these clocks can measure the passage of time extremely accurately. The best ones will be accurate to one second over five billion years.
Accurate time measurement is important for many things, and notably the global network of GPS satellites that offers positions for planes, ships, and ordinary motorists. If the clock of a GPS satellite is inaccurate by a mere one billionth of a second, the position identified on the ground will be around 30cm wrong. If the satellite’s clock were to be out by an entire second, then Google Maps might indicate your position as being closer to the Moon’s surface than to Earth’s.