From the Lab: French mission confirms one of Einstein's General Relativity principles

One of the core principles of Albert Einstein's theory of General Relativity called the equivalence principle, was recently confirmed by the French space agenct's MICROSCOPE satellite mission.

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An illustration of the MICROSCOPE satellite which was launched in 2016. © CNES/ill./DUCROS David, 2016

The objective of the MICROSCOPE mission, which was developed by CNES and launched in 2016 into a low-earth orbit, was to test the principle which states that all bodies fall in the same way in the vacuum.

According to Thibault Damour, a permanent professor at the Institut des Hautes Etudes Scientifique (IHES), who is a member of the MICROSCOPE science working group, the mission aimed to compare the free fall of different materials in orbit around the earth. 

"The main experiment was the comparison of two cylindrical objects made of platinum and titanium. A parallel set of two cylindrical test masses made of platinum was for the quality of the test of measurements," Damour said.

"After analysing two years of data, the test masses of platinum and titanium were found to fall in the same way in the gravitational field of the earth at an unprecedented accuracy (of 10 to the power -15)," he added.

According to Damour, Einstein used the property of equivalence between inertial forces and gravitational field as a fundamental principle to build the theory of general relativity. 

Damour added that though the equivalence principle has been confirmed by the MICROSCOPE experiment, it will important to do further tests "because finding a violation at a very small level would be a new, fundamental discovery in physics."