One idea for how the universe began is that the universe may have appeared out of nothing due to some quantum effect, such as quantum tunneling. In the 1980s, Stephen Hawking and James Hartle further elaborated on this idea by suggesting that time did not exist before the beginning of the universe, leading them to conclude that the universe has no initial boundary conditions on either time or space. The idea is called the “no-boundary proposal” or the “Hawking-Hartle state.”
Source:
https://phys.org/news/2019-05-stabilizing-no-boundary-universe-quantum.html