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Microscope

Exploring the limits of the equivalence principle
Tower of Pisa. Crédits : Bernard Maybon

Tower of Pisa. Crédits : Bernard Maybon

In the XVIIth century, Galileo dropped 2 objects of different weights at the same time from the top of the Tower of Pisa. The objects hit the ground at exactly the same moment, leading him to deduce that the speed of fall of a heavy object in free fall in a vacuum is not proportional to its weight. This discovery underlies what is now called the equivalence principle.

From Galileo to Newton and Einstein, this principle has occupied the minds of the world’s most eminent physicists?



It has inspired Einstein’s famous general theory of relativity and sustained efforts to understand a phenomenon of fundamental importance for which a perfect scientific explanation has yet to be found: the force of gravity that stars exert on all objects.

Testing of the equivalence principle is based on the universal nature of free fall. It has recently been verified on the ground with a relative precision approaching 10-13. Today, CNES is set to go one step further by studying the relative motion of 2 bodies in space, using the permanent free-fall conditions of an orbiting satellite.

The objective of the Microscope satellite, scheduled to be launched in 2011, is therefore to test the validity of the equivalence principle using space-based measurements. The challenge is to achieve a degree of precision 100 times greater than any experiment ever performed on Earth and open up new horizons for gravitational theories.
Microscope microsatellite
(Micro-Satellite à traînée Compensée pour l’Observation du Principe d’Equivalence)
Initiators ONERA, Observatoire de la Côte d’Azur
Status In development
Participants CNES, ONERA, Observatoire de la Côte d’Azur, ESA, ZARM
Objective Test the validity of the equivalence principle with a degree of precision 100 times greater than anything yet achieved
Launch date 2011


Last updated: March 2008

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