The force we experience most intimately remains the most mysterious. Physicists understand how vast migrations of particles called photons light up our homes, and how swarms of “gluon” particles hold together the cores of our atoms. But they can’t say what gravity particles, if any, delight us as babies by enabling our spoons to plummet to the floor. The force of gravity has proved so difficult to account for in terms of particles that many physicists have abandoned that approach altogether. They consider the possibility that gravity — and with it, reality as a whole — might instead be made of tiny strings or other strange things.
But in one corner of the theoretical-physics world, the particle approach is staging a comeback. A growing band of physicists has been using the typical approach to particle physics, known as quantum field theory, for gravity. Although this use of the theory was long considered fatally flawed, these physicists are now finding that it works far better than their predecessors expected.
“So far there is no hint telling us that we should throw quantum field theory away; actually, it’s the opposite,” said Luca Buoninfante (opens a new tab), a theoretical physicist at Radboud University in the Netherlands whose calculations have helped shore up the old theory. When you apply the standard quantum field theory to gravity, you don’t just get a unique theory called quadratic gravity, he said. “You also get new predictions.”
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