Sabino Matarrese

A pebble drops into a pond, and neat circles spread across the water. But the pond's bottom is strewn with invisible glass shards: each one slightly delays the wave, scatters it here, or alters its pace. That's roughly how gravitational waves, the trembling of space itself, pass through distant galaxies and dark clumps of matter.

Right after the Big Bang, space rippled with gravitational waves, like those from a thrown stone. These tremors in the very fabric of the cosmos, predicted by Alan Guth, stretched across the entire universe. The ripples slightly compressed primordial matter in some places and thinned it out in others.