Yale University has received a grant from the W. M. Keck Foundation to fund experiments that researchers hope will provide new insights into quantum gravity. Jack Harris, associate professor of physics, will lead a Yale team that aims to address a long-standing question in physics — how the classical behavior of macroscopic objects emerges from microscopic constituents that obey the laws of quantum mechanics.

Very small objects like photons and electrons are known for their odd behavior. Thanks to the laws of quantum mechanics, they can act as particles or waves, appear in multiple places at once, and mysteriously interact over great distances. The question is why these behaviors are not observed in larger objects.

Scientists know that friction plays an important part in producing classical behavior in macroscopic objects, but many suspect that gravity also suppresses quantum effects. Unfortunately, there has been no practical way to test this possibility, and in the absence of a full quantum theory of gravity, it is difficult even to make any quantitative predictions.

To address this problem, Harris will create a novel instrument that will enable a drop of liquid helium to exhibit quantum mechanical effects. “A millimeter across,” Harris said, “our droplet will be five orders of magnitude more massive than any other object in which quantum effects have been observed. It will enable us to explore quantum behavior on unprecedentedly macroscopic scales and to provide the first experimental tests of leading models of gravity at the quantum level.”

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