Timekeepers in space Atomic clocks on the ISS space station to prove Einstein theory

Is Einstein's assumption about gravity and time correct? Researchers want to find out with the help of two clocks. And are sending them into space to do so.

With two atomic clocks in space, Europe wants to learn more about the relationship between gravity and time. After several hours of maneuvering with a robotic arm, the Earth-facing instrument Aces is now attached to the Columbus module of the International Space Station ISS. It is said to send the most accurate time signal from space to date.

According to the European Space Agency Esa, Aces consists of two clocks: Pharaoh and SHM. The cesium atomic clock Pharao measures the seconds with particular precision. For a continuous signal, however, a second clock is required, which does not have to be extremely accurate, but must be stable: the hydrogen maser clock SHM (Space Hydrogen Maser).

Time passes measurably faster at higher altitudes

The signals are to be sent to several ground stations every day. Experts then want to see how time differs on the ground and on the ISS. They hope to gain insights into Albert Einstein's general theory of relativity. Einstein assumed that gravity basically slows down time. According to Esa, experiments on Earth have already shown that time passes more quickly at higher altitudes.

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However, Aces will not only help to verify Einstein's assumptions. For the first time, the project also aims to network all accurate clocks around the world, said Simon Weinberg, who is responsible for Aces at Esa. "Once we get this up and running, we will be able to share the standard for seconds worldwide."

First of all, however, Aces will need about six months of calibration work. The scientific community should receive the first results in a year and a half.