The early universe grew at a terrifying speed — inflating to gigantic proportions in a tiny fraction of a second. Physicists describe this burst with a single number: the exponent in a formula that resembles the steepness of a hill. The steeper the hill, the faster the ball rolls down: that is, the more rapidly space expanded.

For a long time, it was thought that simple hills with gentle slopes (say, like a sand dune) didn't work: they painted a picture of the sky that didn't match what telescopes see. But the authors of this work added an invisible ripple to space itself — quantum corrections to volume that become noticeable only at mind-boggling densities. This ripple acts like a headwind: it slightly slows the ball, changing its trajectory.

As a result, old models with exponents 1/3, 2/5, and 2/3, like recut sails, once again catch the wind of observations. Without the quantum ripple, they missed the target; with it, they neatly fit into the tight corridors set by the most precise maps of the cosmic microwave background.