AN ATOMIC clock so accurate that it should lose only 1 second in 150 million years is being tested in the GPS satellite navigation system. It promises to be the most stable clock ever built and, if it works, will replace the clocks that are now national standards against which a country’s other clocks are set.
Atomic clocks keep time by tracking the waves atoms emit as they oscillate between different energy levels. Every atom of a particular element emits at exactly the same frequency, so seconds are measured by counting the number of waves.
One of today’s standard clocks…
