The early universe underwent a rapid expansion — inflation. In a tiny fraction of a second, minuscule quantum jitters were stretched to galactic scales and became the seeds of all large-scale structure. But physicists have long worried: could effects from the very smallest distances, the so-called renormalization sector, spoil this picture?

The authors of the new work show that inflation solves the problem on its own. While perturbations that have crossed the horizon (the distance light has traveled) freeze, all the controversial corrections rapidly weaken. It's like a conductor who dampens extraneous noise in an orchestra, leaving only a pure melody.

The result is encouraging: the observed spectrum of primordial inhomogeneities is almost insensitive to "renormalization ambiguities." Standard predictions of inflation, on the scales we can access, turn out to be surprisingly sturdy. The cosmos itself ensured that its master blueprint does not depend on indistinguishable details.