When a grain of sand falls on a table, its impact is predictable. But if you squeezed it down to the size of an atomic nucleus, the familiar laws of gravity would break down — the force of gravity would grow without bound. The asymptotically safe approach to quantum gravity offers a way out: at a certain scale, like a river calming after rapids, the growth of the force stops. This property is called quantum scale symmetry — the laws cease to depend on how finely we look.
For a long time, calculations confirmed such symmetry only in a simplified world — without matter and with "frozen" time. Now, according to the review, physicists have stepped into reality. They included the Standard Model particles, the flow of time, and even dark matter candidates. It turned out that the symmetry holds, as if nature at the deepest level itself avoids infinities. This is not just a mathematical trick: the calculations allow us to compute how the first moments of the universe behaved or what happens at the center of a black hole.
Now the theory is becoming precise enough to compare with observations — for example, data on gravitational waves or the cosmic microwave background. This is like tuning a radio: before we heard only static, but now we are beginning to make out the voice of gravity itself.
The idea of asymptotic safety first arose in particle physics, but for gravity it was proposed by Steven Weinberg in 1979—and only now have calculations become powerful enough to test it.
In Carl Sagan's novel "Contact," aliens use wormholes, whose stability could indeed be explained by quantum gravity.