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Physics: MICROSCOPE verifies a pillar of Einstein’s theory

The MICROSCOPE space mission has achieved record accuracy in verifying physics’ “equivalence principle”, which tests Einstein’s general relativity, according to several studies whose results were presented on Wednesday.

Launched in 2016, MICROSCOPE was installed in orbit at an altitude of 710 km, and provided data for two and a half years.

The micro-satellite, built by the CNES (National Center for Space Studies), housed two T-SAGE accelerometers from ONERA, the French center for aerospace research. The latter was also responsible for data processing, thanks to the simulation and data processing tools developed by the Côte d’Azur Observatory.

It all starts with Galileo, in the 17th century, who postulated that by releasing two bodies of distinct mass and composition at the same time, they hit the ground at the same time. Three centuries later, an astronaut of the Apollo XV mission will illustrate this by dropping, apparently at the same speed, a feather and a hammer on the surface of the Moon.

Meanwhile, Newton postulated the “principle of equivalence” between the gravitational force and the force of inertia that a body would undergo in a situation of acceleration.

This principle is a pillar of Albert Einstein’s theory of relativity, which describes gravitation as a curvature of spacetime distorted by matter.

It has been verified on Earth with a degree of relative precision up to the 13th decimal place in 2007. But space is the ideal environment to go further, freeing itself from multiple disturbances specific to the Earth’s surface.

The result presented on Wednesday, which is the subject of publications in the prestigious journals Physical Review Letters and Classical Quantum Gravity, verifies the principle of equivalence with a measurement precise to the fifteenth decimal place.

MICROSCOPE has compared, using an accelerometer, the forces necessary to keep two cylinders of different mass and composition immobile, suspended in a small vacuum container and subjected to the Earth’s gravitation.

To verify the principle of equivalence was to verify that the two forces were equal. All with a precision whose “equivalent would be to measure the weight of a fly on a super-tanker of 500,000 tonnes”, explained Manuel Rodrigues, an experiment manager at ONERA, presenting the results to the CNES headquarters.

The performance of the measurement was based both on a satellite control system making it possible to obtain almost perfect stability, and on data processing correcting spurious signals, such as for example “cracks” due to deformations of the coating isolating the machine under the effect of the sun.

Future projects, such as MICROSCOPE2, aim to further refine the measurement. With the challenge of further testing one of the pillars of the theory of general relativity. And beyond that, to test the models aiming to unify the theory of relativity with quantum theory, which for the most part predict violations of the principle of equivalence.