Physics

A quantum test of free fall

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Science  29 Jul 2016:
Vol. 353, Issue 6298, pp. 459-460
DOI: 10.1126/science.353.6298.459-g

The Leaning Tower of Pisa, Italy

PHOTO: © STEFANO POLITI MARKOVINA/ALAMY STOCK PHOTO

Galileo Galilei is purported to have dropped objects of different mass from the Leaning Tower of Pisa to demonstrate that they fall at the same rate. In formulating his general theory of relativity, Einstein described this as the universality of free fall—that all objects, irrespective of their mass, will behave identically when subject to the same gravitational field. Taking this into the quantum regime, Duan et al. performed Galileo's drop experiment with rubidium atoms of different quantum mechanical spins. With a sensitive atom-interferometer setup, they showed that the atoms fall at the same rate to within one part in 10 million, upholding Einstein's universality proposition for now. While we await a theory that can unify relativity and the principles of quantum mechanics, such precision-based experimental tests should help place bounds on any proposed theories of quantum gravity.

Phys. Rev. Lett. 117, 023001 (2016).

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