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April 2019, ScientificAmerican.com 49

Physicists attempting


to unify the theories of


gravity and quantum


mechanics have long thought practical experiments


were out of reach, but new proposals offer a chance


to test the quantum nature of gravity on a tabletop


By Tim Folger


Photographs by Mattia Balsamini

QUANTUM


PHYSICS

IN BRIEF

To unify the famously uncooperative theories of
quantum mechanics and general relativity, scien-
tists will likely have to reach down to the unimagin-
ably small realm of the “Planck scale.” Practical
experiments probing this scale have long been

thought impossible, but several new proposals
stand to change that.
Physicists are hoping that by making extremely
precise measurements of gravity in small-scale set-
ups—experiments that will fit onto a tabletop in a

laboratory—they can detect effects from the inter-
section of gravity and quantum theory.
The experiments aim to show whether gravity
becomes quantized—that is, divisible into discrete
bits—on extremely tiny scales.

GRAVITY IN


THE LAB


© 2019 Scientific American © 2019 Scientific American

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