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. They are thinner than an atom, but the mass of one such crack is comparable to thousands of galaxies. Trembling, like shuddering fissures, they emit gravitational waves — ripples in the very fabric of spacetime.
These waves have already shown up in the timing glitches of the universe's ultraprecise 'lighthouses' — neutron stars, or pulsars. Pulsar observation data have hinted at the walls' existence. Now researchers have figured out how the future space antennas LISA and Taiji could confirm the signal. Ground-based detectors already pick up low frequencies, while space-based ones will catch the higher notes of these vibrations. Joint analysis of data from ground and space will dramatically boost the chances of discovery. If the instruments register even a faint echo, it will prove that space still harbors cracks from the moment the world was born.
A domain wall's thickness is billions of times smaller than an atom. If you encountered one, you'd feel nothing, but its gravitational echo could reveal the secrets of the universe's birth.