An experiment not much bigger than a tabletop, using ultra-cold metal plates, could serve up a cosmic feast. It could give us a glimpse of quantum gravity
and so lead to a "theory of everything": one that unites the laws of quantum mechanics, governing the very small, and those of general relativity, concerning the monstrously huge.
Such theories are difficult to test in the lab because they probe such extreme scales. But quantum effects have a way of showing up unexpectedly. In a strange quantum phenomenon known as the Casimir effect, two sheets of metal held very close together in a vacuum will attract each other.
The effect occurs because, even in empty space, there is an electromagnetic field that fluctuates slightly all the time. Placing two metal sheets very close to one another limits the fluctuations between them, because the sheets reflect electromagnetic waves. But elsewhere the fluctuations are unrestricted, and this pushes the plates together.
James Quach at the University of Tokyo suggests that we might be able to observe the equivalent effect for gravity. That would, in turn, be direct evidence of the quantum nature of gravity: the Casimir effect depends on vacuum fluctuations, which are only predicted by quantum physics.
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