Einstein’s equivalence principle reaffirmed – satellite experiment measures mass response to gravity more accurately than ever


Tested in Space: The basic physical theory of weak equivalence has passed its toughest test ever – and thus once again confirmed Einstein’s theory of relativity. The satellite experiment MICROSCOPE investigated whether gravity acts equally on two different test masses. For the first time, the validity of the equivalence principle was set to 10. was extended to-15 Absolutely confirmed. As physicists report, this greatly reduces the space for the theory of relativity to expand.

Galileo Galilei saw it, Isaac Newton expressed it, and Albert Einstein made it a pillar of his general theory of relativityThe principle of weak equivalence states that, in the absence of other forces, gravity and acceleration act the same way on all objects—regardless of their mass and composition. For example, a feather and a lead ball fall with the same speed in a vacuum.

The validity of this equivalence principle has been tested and confirmed in a number of experiments, including laboratory and in-Earth orbit drop tests and laser measurements of lunar distances. However, to rule out deviations due to novel quantum physical effects or as yet undiscovered particles, such tests must be extremely accurate.

The MICROSCOPE satellite has test masses whose gravitational response is measured. © Onera

Floating cylinders as test objects

The most accurate review of the equivalence principle to date is now available. They are based on an experiment on board the microsatellite MICROSCOPE, which orbited Earth in a Sun-synchronous low orbit from 2016 to 2018. For the weak equivalence test, electrostatic forces held two pairs of test masses in suspension. The highly sensitive acceleration sensor recorded every movement of the test mass.

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A pair of test masses consists of two cylinders of equal weight and size made of a heavy platinum-rhodium alloy and served as a reference. In the second pair, one of these test masses was exchanged for a lightweight titanium-aluminum cylinder. If the satellite now changes its orientation to Earth and thus into the planet’s gravitational field, this affects the test mass. If the reactions of unequal test masses deviate from each other and from the reference, this represents a violation of the principle of equivalence.

Already in 2017, the team led by mission leader Pierre Touboull from the research center ONERA in Paris first result of the published satellite experiment, in which 10. The equivalence principle was used with an accuracy of-14 Confirmed.

Equivalence reaffirmed

Meanwhile, physicists evaluate the data from the microscope experiment every two and a half years and do a comprehensive analysis of possible sources of error and uncertainty factors as well. The result: “We found no violation of the weak equivalence principle and thus set the strictest limit ever to its validity,” report Tuboul and his team. His tests gave 10 . achieved accuracy of-15,

As a result, this verification of the equivalence principle also excludes deviations from this aspect of the theory of relativity to this level. “We also set new and improved limits for any future theory,” says co-author Gilles Matrice from the Cte ​​d’Azur Observatory. Because if there are still unknown particles or forces that cause deviations from the equivalence principle, their effects can only appear outside the limits that have now been determined.

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“New Physics” Limits

This is relevant, for example, for the search for dark matter particles or large-scale interactions. “At the same time, the MICROSCOPE experiment paves the way for new, even more ambitious tests of the equivalence principle in space,” the team explains. “However, we do not expect further improvements in the accuracy of such tests over the next decade or two.” (Physical Review Papers, 2022; doi: 10.1103/PhysRevLet.129.121102,

Source: American Physical Society

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