MORE than 400 years after Galileo reputedly dropped two cannonballs from the Leaning Tower of Pisa, French scientists are planning to recreate the experiment in space鈥攁nd hoping to prove him wrong.
Galileo showed that the two balls would land at the same time, despite having different masses. Whether the story is true or not, this understanding eventually led to Einstein鈥檚 equivalence principle: gravity and acceleration have an equivalent effect on mass. This principle underlies the general theory of relativity.
The space-based experiment, called MICROSCOPE will be launched by ESA in 2004 to test this principle much more accurately than ever before. Like Galileo, MICROSCOPE will watch two metal objects as they fall. But this time the objects will be cylinders made of platinum and titanium floating inside a satellite 1000 kilometres above Earth. 鈥淚n orbit you are in permanent free fall,鈥� explains project investigator Pierre Touboul at the French aerospace research centre ONERA, which is organising the mission. If the equivalence principle fails the cylinders will drift apart.
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The principle has already been tested in Earth-based experiments to an accuracy of one part in a trillion but noise from seismic activity means these techniques have reached their limit. 鈥淲e expect to be about a thousand times more accurate,鈥� says Touboul.
If the test falsifies the equivalence principle that could reveal a new force of nature. 鈥淚t would constitute the discovery of a new, long-range force coupled to gravitation,鈥� explains Francis Everitt, a gravitational physicist at Stanford University.