Taking both paths
Experiment put atoms in a superposition of trajectories to find out.
How do you get two quantum states to interfere when one involves moving and the other doesn't?
ALIOUI Mohammed Elamine
Almost a hundred years ago, physicists theorized out what free fall should do to a quantum wave. If the solution they came up with is wrong, quantum mechanics and Einstein’s theory of gravity flatly contradict each other. But testing it has been impossible because nobody has managed to build an interferometer that could perform the necessary measurement.
