National Physical Laboratory

Optical clocks perform new test of special relativity

An international collaboration involving the National Physical Laboratory (NPL) has used optical atomic clocks to perform the most accurate test yet of time dilation predicted by special relativity, as featured in New Scientist.

NPL's strontium lattice clock
NPL's strontium lattice clock

Optical clocks at NPL, SYRTE (France) and PTB (Germany) were compared using two state-of-the-art optical fibre links (supported by LPL, France), between London and Paris, and Paris and Braunschweig.

One of special relativity's fundamental assumptions is that there is no preferred frame of reference in the Universe – for example, there is no 'aether', the presence of which Michelson and Morley unsuccessfully tried to demonstrate in their famous 1887 experiment. If there were a preferred frame of reference, we would expect to see variations in the rate a clock ticks at, as it rotates with the Earth and constantly changes direction in space.

The team looked for these daily variations by comparing four optical clocks across three different locations. They analysed the clock's frequencies – their tick rates – to calculate a parameter called alpha, which should be zero if the theory of special relativity is correct. The results showed that alpha is less than 10-8 – a result twice as accurate as the best previous limit, and two orders of magnitude better than that calculated from past experiments using caesium clocks

Observed violations of special relativity could provide vital clues to physicists looking to link Einstein's theory of general relativity with quantum mechanics. Optical clocks, based on the probing of atoms or ions with lasers, are the most precise measurement devices in the world and their unparalleled performance makes them ideal for tests of fundamental physics, such as bounding the time variation of fundamental constants.

This work is the first of a new generation of tests of fundamental physics using optical clocks and fibre links. As clocks improve, and as fibre links are routinely operated, the researchers expect that these tests will improve by orders of magnitude in the near future.

Read the full article in New Scientist

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Last Updated: 31 Mar 2017
Created: 29 Mar 2017


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