Precisely testing the speed of light

Australian and German researchers have completed testing that has effectively measured the spatial consistency of the speed of light with a precision 10 times greater than ever before.

Their testing also confirmed a core component of Einstein’s theory of relativity known as ‘Lorentz symmetry’, which predicts that the speed of light is the same in all directions.

The researchers, from The University of Western Australia (UWA) and Humboldt University of Berlin, compared extremely pure microwave frequency signals from two cryogenic sapphire oscillators against each other. The experiment placed the microwave oscillators perpendicular to each other and rotated them on a turntable once every 100 seconds over the course of a year.

“The frequency of the microwave signals directly linked to the speed of light,” said Dr Stephen Parker from UWA’s Frequency and Quantum Metrology Research Group.

“If this were to change depending on the direction it was facing, it would indicate that Lorentz symmetry had been violated. But the frequencies didn’t even change down to the 18th digit (the smallest part of the measurement of frequency), which is remarkable that this symmetry of nature still holds true at such tiny levels.”

Having published their results in the journal Nature Communications, the research team is now in the process of upgrading their experiment and incorporating new optical light sources, which would open up possibilities for future research.

“This will allow us to improve the sensitivity of our work and explore other ways that Lorentz symmetry could be broken,” Dr Parker said.

“Searching for possible violations of Lorentz symmetry will provide valuable clues for a more comprehensive and unified theory.”

Image caption: Dr Stephen Parker with the cryogenic sapphire oscillator.

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