A new experiment, based on measuring the free fall of rubidium atoms in a vacuum, confirms that atoms of different quantum spin experience identical acceleration due to gravity.
The result is important in the quest to unify general relativity with quantum mechanics, and may already rule out some proposed theories of quantum gravity.
Now, a new breed of experiments is allowing physicists to measure the force of gravity at the scale of quantum objects and so test, for the first time, some of the theories proposing to bridge the chasm between gravity and quantum mechanics.
In the new work, a team of Chinese scientists from Huazhong University of Science and Technology in Wuhan has compared the acceleration of rubidium atoms due to gravity and found it to be identical regardless of the orientation of the atom’s spin.
Although the equivalence principle is central to general relativity, many quantum theories of gravity, which attempt to describe gravity using quantum mechanics, predict that the equivalence principle could be violated.
In particular, some quantum properties, such as the spin of an atom, might affect free fall the theories say.
This is the first time gravity has been tested in terms of quantum spin.