For a long time (i.e. Galileo), we have known that 1 kilogram of lead falls as quickly as 1 kilogram of feather – if however no force other than gravity applies to it, for example the friction of the air, what you get in a vacuum. However, between 2016 and 2018, a satellite, Microscope, in orbit at an altitude of 710 kilometers, tested this four-hundred-year-old certainty by reiterating body fall experiments.
The verdict, published Wednesday, September 14, in twelve articles, in Physical Review Letters et Classical and Quantum Gravity, is clear: Galileo was right.
The difference in acceleration between two bodies in free fall is less than 10-15.
And not just a little. His observation remains correct, as precisely as the researchers were able to verify: the difference in acceleration between two bodies in free fall is less than 10-15. Consider a precision thanks to which one might detect the weight of“a half microgram fly on a 500,000 ton supertanker”.
The image, which comes to greet an unprecedented record, was used by Manuel Rodrigues, project manager and member of the National Office for Aerospace Studies and Research (Onera), during a press conference on Wednesday.
Galileo had measured up to a difference of 1 thousandth (10-3). The result obtained is also a hundred times better than that provided by other measurements made on Earth in 2007, and ten times better than the preliminary conclusions of Microscope in 2017.
Another victory for general relativity
With such precision, it was even Albert Einstein who was right. To develop his famous theory of general relativity, in 1915, he raised Galileo’s observation as a founding principle: a falling body is like an accelerating object. Gravity and acceleration are equivalent.
But the experiment was not intended for the history of science, rather for their future. The researchers wanted to see if microscopic forces might have been overlooked by Einstein and others, and whether they would slow down or accelerate the masses. This heresy is not so reckless, since evidence already exists that general relativity does not explain everything, for example the abnormal rotation of galaxies or the acceleration of the expansion of the Universe. And, inevitably, a replacement theory would be synonymous with new forces or particles.
The construction of the 300-kilogram satellite of the National Center for Space Studies (CNES), designed by Onera and whose data has been analyzed by the Observatory of the Côte d’Azur with a large number of researchers from the National Center for scientific research (CNRS), was therefore decided twenty-five years ago, with the aim of finding a hitch in the principle of equivalence.
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