Atomic-scale free-fall test aboard Tiangong confirms Einstein’s equivalence principle
Researchers on China’s Tiangong space station dropped two clouds of rubidium atoms with different nuclear masses and found their accelerations matched to within 0.05 thousandths of a percent.
A team of physicists conducted a modern version of Galileo’s falling-weight experiment using ultra-cold rubidium atoms aboard China’s Tiangong space station. By preparing two separate atomic clouds with differing numbers of neutrons, they created samples with distinct gravitational and inertial masses. In the microgravity environment of orbit, the clouds were released and their relative accelerations were tracked with high precision.
The results indicated the two clouds accelerated identically, matching to within 0.05 thousandths of a percent, thereby confirming that gravitational and inertial mass are equivalent at the atomic scale. This verification of the weak equivalence principle extends previous Earth-based tests and reinforces a core tenet of Einstein’s general theory of relativity. The study appeared in the August 28 issue of Science Advances.
Why it matters
It shows that Einstein’s key gravity principle holds true even for quantum-scale objects in space.
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