…“So far there is no hint telling us that we should throw quantum field theory away; actually, it’s the opposite,” said Luca Buoninfante, 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.”…

…Perhaps effects occasionally sneak ahead of their causes at the microscopic level, for instance. And perhaps negative-energy “ghost” particles that arise in quadratic gravity can exist safely in the equations without creating paradoxes in experiments…

…The surprising successes of quadratic gravity hint that gravity may yet turn out to have a blurry picture that works well enough after all. Below a certain spatial scale, it may be that any complicated details — whether those are strings, loops or nothing at all — can be ignored, and you’ll still get a fully consistent theory. If that’s the case, physicists can accurately predict how gravitons collide and how the universe inflated without worrying about what’s truly going on at the smallest scales. “It may or may not be the ultimate theory,” Donoghue said. But maybe “it becomes a closed, self-consistent layer of reality.”…