A key tenet of Albert Einstein’s general theory of relativity has passed yet another test with flying colors-and for the first time in space. A French satellite experiment has shown that objects with different masses fall at exactly the same rate under gravity, just as relativity dictates.
Physicists scrutinize the equivalence principle because any violation could point to new forces of nature that might resolve a long-standing impasse between general relativity and quantum theory.
The satellite, called MICROSCOPE, found no discrepancy in the acceleration of two small test masses to about one part in 100 trillion.
As the satellite traces out a 1.5-hour-long orbit, a characteristic rise and fall in the difference between the two applied voltages would indicate that one of the cylinders is falling slightly faster than the other-and signal a violation of the equivalence principle.
A proposed Italian satellite, aptly named Galileo Galilei, would test equivalence to a precision of one part in 1017, partly by spinning rapidly and isolating any signal from more slowly varying systematic effects.
Anna Nobili, a physicist at the University of Pisa in Italy and Galileo Galilei principal investigator, admits that finding the money for another space mission will not be easy.