ATOMIC clocks, currently the size of fridges, could shrink to the microscale thanks to a new way of measuring the second. The technique could also see aluminium displace caesium as the standard of time.

The world’s most accurate atomic clocks are at the National Institute of Standards and Technology (NIST) at Boulder, Colorado. Known as fountain clocks, they send clouds of caesium atoms through a vacuum chamber in a magnetic field. Large atoms like caesium and aluminium have multiple energy levels that are so close together they appear indistinguishable. The magnetic field separates these levels into two “hyperfine” states.

The …