THE International Space Station could one day carry the world’s most accurate
clock, providing an orbiting time reference everybody on Earth can use. This
plan for what will be called the Primary Atomic Reference Clock in Space (PARCS)
was put forward at last week’s American Physical Society meeting in Long Beach,
California.
Most atomic clocks keep time by counting the oscillations of caesium atoms,
which define the official length of a second. On Earth, gravity limits such
clocks’ accuracy because researchers have, at best, about a second to measure
the caesium frequency before atoms fall from their measurement position. But…
