This episode of the Physics World Weekly podcast features the laser specialist Tara Fortier, who works with some of the world’s best atomic clocks. Based at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, she explains how atomic clocks work and why it is important for scientists to be able to compare the time signals of different clocks around the world.

The interview also delves into scientific and technological applications of atomic clocks such as testing Albert Einstein’s general theory of relativity and searching for physics beyond the Standard Model.

Also in this podcast, John Collier, director of the UK’s Central Laser Facility​, talks about a proposal to build a free electron laser in the UK.