Nature Commun. http://dx.doi.org/10.1038/ncomms9174 (2015)

The hunt for new physics — or hints of the elusive relationship between quantum mechanics and general relativity — relies on spotting tiny violations of known principles such as Lorentz invariance. But no such illegal activity has yet been reported, which motivated Moritz Nagel and colleagues to use the latest technologies in a modern Michelson–Morley-style experiment to perform the most precise measurement of the spatial isotropy of the speed of light.

In the original Michelson–Morley experiment, the interference pattern of light travelling along the two perpendicular arms of an interferometer and back would betray any change in the speed of light due to its motion relative to the aether. In the modern version, reported by Nagel et al., any anisotropy in the speed of light would be reflected in the modification of the beat note frequency between two orthogonal ultrastable oscillators.

A year's worth of data checking for various rotations, both artificial and those due to the Earth's movement, constrained the fractional frequency change below 10−18 — ruling out any sign of Lorentz symmetry violation: either a reassuring or disappointing result, depending on your taste.