Summary
Hypothetical humongous sheets of spacetime could divide one region of the universe from another. Such so-called domain walls are the natural outcome of theories that try to solve some of the deepest mysteries in physics. If they formed after the big bang, by today they’d be the dominant source of energy in our universe.
Domain walls can arise from scalar fields that exhibit “discrete” symmetry, meaning that the fields can have two (or more) different states with the same energy. A team led by Cheng Chin, an experimental physicist at the University of Chicago, demonstrated the formation of domain walls in a collection of about 40,000 atoms.
Researchers have known that domain walls can dissipate if the discrete symmetry is not exact. This could explain why we don’t see domain walls today. The new study is “an important step toward understanding the gravitational waves produced by domain-wall decay,” Takahashi says.
Domain walls are bubbles of spacetime bigger than the radius of the observable universe. As cosmic history unfolded and spacetime expanded, these bubbles and their domain walls would eventually enter the observable world. Such structures would appear as overdense regions of energy. And “an overdense... will collapse to a black hole,” Ferreira says.
