For the first time, physicists have measured the tiny quantum shift an object acquires by falling through Earth's gravity — an effect of Einstein's relativity that was predicted almost a century ago but never observed.
Researchers placed ultracold rubidium atoms into a superposition, a quantum state in which a single particle takes two paths at once. In this experiment, one path put the atom in free fall while the other kept it motionless. Recombining the atoms revealed an almost imperceptible difference between the two paths.
The measurement, published Sept. 2 in the journal Science Advances, shows that Einstein's equivalence principle — the idea at the heart of general relativity — still holds when it is pushed into the quantum world, creating a small but tantalizing link between relativity and quantum mechanics.
"The principle says that acceleration and gravity cannot be distinguished locally," Read Entire Article
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