In an unprecedented step, researchers crafted a detailed model compatible with the universe’s accelerated expansion.

In 1998, astronomers discovered dark energy. The finding, which transformed our conception of the cosmos, came with a little-known consequence: It threw a wrench into the already daunting task of finding a version of string theory that describes the universe we live in.

Dark energy is a “positive” energy that causes our universe to expand at an accelerating rate. But the best-understood models of string theory describe universes with energy that is either negative or zero.

Of the various criticisms made of string theory through the years — that it only works in a 10-dimensional universe, that its fundamental constituents, tiny strings, are too small to ever be observed — this was perhaps the most troubling. String theory appeared to be useful only for describing a universe with a negative “anti-de Sitter” geometry, whereas we live in a universe with a positive “de Sitter” geometry.

Then last year, two physicists offered a stripped-down but precise formula for how string theory could give rise to a universe similar to ours(opens a new tab) — a de Sitter universe undergoing accelerated expansion.

“It is the very first example [from string theory] of an explicit de Sitter space,” said Thomas Van Riet(opens a new tab) of KU Leuven in Belgium.

...read more at quantamagazine.org