Atomic clocks in space test Einstein's theory

(CONNECT) An ensemble of atomic clocks (Atomic Clock Ensemble in Space, ACES) is to clarify in space whether the general theory of relativity corresponds exactly to reality. It states that time passes at different rates depending on the force of gravity. However, it has not yet been proven that the differences in the speed of time correspond exactly to what Albert Einstein described. "We don't know whether there is a deviation between the measurements and what the theory predicts," explains Philippe Jetzer in a report from the University of Zurich (UZH). He is Professor of Theoretical Physics at UZH and leads the ACES Topical Team for General Relativity at ESA. He is therefore jointly responsible for the theoretical foundations of the project.

On Easter Monday, the ESA experiment was transported from NASA's Kennedy Space Center to the International Space Station ISS on a Falcon 9 launcher. The experiment consists of a cesium atomic clock and a hydrogen maser, a type of laser that emits microwaves instead of light, developed and built by the Neuchâtel-based company Safran Time Technologies. Together, they reportedly produce the most precise time signal ever generated in space. Over a period of 300 million years, it deviates by a maximum of one second.

After a commissioning and calibration phase lasting several months, ACES will transmit a time signal to a network of atomic clocks at various locations on Earth over a period of 30 months. This allows the time signals on Earth and from space to be compared with each other. "If ACES measures a deviation from the predictions in the theory of relativity, that would be a sensation," says Jetzer. In this case, these deviations could possibly be explained by quantum effects. "This would be a first rapprochement between the two major fundamental theories of modern physics, which have yet to be reconciled." ce/mm