Rome Samanta

When water freezes in a lake, the ice becomes covered with a network of cracks — boundaries between crystals. A similar process in the first moments after the Big Bang could have spawned enormous structures resembling icy fractures. Scientists call them domain walls.

The early universe cooled like a giant cauldron. And just like cracks can form on a freezing pond, cracks could appear in space — domain walls. These are folds in space itself, boundaries between regions with different properties. When such a wall vanished, it shook spacetime, producing gravitational waves.