I was sitting on a chair in the Patent Office in Bern when suddenly I had an idea: when a man is in free fall, he does not feel his own weight . I was amazed . This simple thought experiment made a deep impression to me and took me to the theory of gravitation .
Albert Einstein , Kyoto , 1922

This is the idea that Einstein founded the theory of general relativity : a man trapped in an elevator in free fall not clear if he does not feel its weight because the elevator in free fall , or because that it is jettisoned in space, weightless. In other words , we can not distinguish the gravity of another type of acceleration . Today , physicists wonder about the validity of this ” principle of equivalence ” in the quantum domain . Tim van Zoest , of the Leibniz University in Hanover, and his colleagues have developed a device that would allow them to test this principle on a Bose- Einstein.

Provided by quantum physics , this peculiar state of matter – thousands of atoms cooled to the point where they are all in the same quantum state – is produced in the laboratory for fifteen years: the atoms are cooled laser , then in a magnetic trap . Slow down , they cool down to a few billionths of a degree above absolute zero . The experimental usual fills a room full of vacuum chambers, large magnetic coils , tables and optical electronics. But a few years ago , Jakob Reichel , the Laboratoire Kastler Brossel , Ecole Normale Superieure in Paris and his colleagues have developed superconducting chip , thanks to the magnetic field generated by the current passing through them, these chips are able to trap a cloud of cold atoms and cool it to Bose-Einstein condensation in a few seconds.

Physicists have built a chip with atoms of rubidium 87 in a capsule the size of a man . The capsule contains all the material necessary to prepare and observe the condensate two lasers to pre -cool the atoms , a laser sensor , a vacuum chamber containing the atom chip , power supply , a camera to film continuously condensate and a control computer. Dumped in a high vacuum a height of 146 meters , the capsule landed after 4.6 seconds of freefall in a polystyrene ball pool 8 feet deep.

The Bose-Einstein condensate is formed at the second second of falling and can thus be observed in free fall for a second. During his fall , the condensate is illuminated with laser detection, and the shadow produced is captured by the camera . The researchers have verified that the atoms remain condensed during the fall . To test the equivalence principle , they have now split the condensate into two parts to his training , then recombine them in late fall.

As a light wave, the two parts of the condensate , by recombinant should interfere and form alternating light and dark fringes . The size and spacing of these fringes depend on the speed of the two parts of the condensate , if the equivalence principle is not valid in quantum , the two sides do not will fall at the same speed and then produce fringes slightly different from those predicted by theory .

For metrology , these studies also constitute a major technological step forward : they show that the use of a Bose-Einstein condensate in a small space , subject to vibration , is possible. New horizons open, including the use of these condensates in space, satellites in order to verify more precisely some of the effects predicted by general relativity .