Science NewsCurated by RSF Research Staff Home > Science News > Atomic clocks make best measurement yet of relativity of time Our most accurate clocks are probing a key tenet of Einstein’s theory of relativity: the idea that time isn’t absolute. Any violation of this principle could point us to a long-sought theory that would unite Einstein’s ideas with quantum mechanics. Special relativity established that the laws of physics are the same for any two observers moving at a constant speed relative to each other, a symmetry called Lorentz invariance. One consequence is that they would observe each other’s clocks running at different rates. Each observer would regard themselves as stationary and see the other observer’s clock as ticking slowly – an effect called time dilation. Einstein’s general relativity compounds the effect. It says that the clocks would run differently if they experience different gravitational forces. For two decades, comparing atomic clocks aboard GPS satellites with those on Earth have helped test the effect – and always confirmed it. But since any deviation from relativity would be very subtle, we might need a more precise instrument to find it. Most atomic clocks rely on the frequency of the microwave radiation emitted when electrons in caesium-133 atoms change energy states. Next-generation clocks that use strontium atoms have at least three times the precision, barely gaining or losing a second over 15 billion years. Now, Pacôme Delva of the Paris Observatory and his colleagues have used strontium clocks to test time dilation. Two optical fibre links, one between London and Paris and another between Paris and Braunschweig, Germany, were used to compare devices in these locations. These clocks are moving at different velocities because of their position on the Earth’s surface, and relativity makes precise predictions about the extent of time dilation they experience. For example, a clock closer to the equator should tick more slowly than one closer to the North Pole. After one day, clocks in Paris and London should show a difference of 5 nanoseconds. To compare them, the team synchronised lasers to the frequency of the radiation from each clock’s strontium atoms. Then they transmitted the beams over the fibre-optic links, allowing them to superimpose the lasers to detect any telltale differences in frequency indicating one clock ticking faster than the other. With the measurements, the team calculated a parameter called alpha, which should be zero if there is no violation of Lorentz invariance. The latest results show that alpha is less than 10-8 – a result two orders of magnitude better than from experiments using caesium clocks, and twice as accurate as the previous best limit, obtained by studying electronic transitions in lithium ions moving at one-third the speed of light (arxiv.org/abs/1703.04426v1). Letting the experiments run for longer will improve accuracy even further, says team member Jochen Kronjäger of the UK’s National Physical Laboratory in Teddington. So far so good for relativity. But how would physicists react if a violation of Lorentz invariance is ever measured? “The immediate consequence would be that nobody would believe it,” says Sabine Hossenfelder, a theorist at the Frankfurt Institute for Advanced Studies in Germany. However, if a violation is ever confirmed, the implications would be huge. “Quantising gravity, [the nature of] dark matter and dark energy – these are three big questions for which Lorentz invariance violations would be an extremely important hint as to the nature of the underlying theory,” she says. This article appeared in print under the headline “Networked atomic clocks seek untimely behaviour”; New Scientist, 2017. Report by Anil Ananthaswamy Article: https://arxiv.org/pdf/1703.04426v1.pdf Quantum physics working at macroscopic scaleDecember 9, 2018A nanophotonic structure used to entangle photosynthetic bacteriaDecember 7, 2018The force of the VacuumDecember 5, 2018Unusual Seismic Phenomenon heard around the WorldDecember 5, 2018An approach to manipulate small objects with lightNovember 30, 2018 Sharing is caring - please share this with your friends: Facebook Twitter If you like this content, you will love the Resonance Academy.