Researchers studying the no-boundary wavefunction in Einstein gravity identified families of possible universe histories whose contributions grow exponentially. Some candidate paths fail a mathematical consistency test, while whether the others contribute remains open.
The no-boundary proposal describes the universe’s early state through quantum gravity, so its possible histories must combine into a well-defined quantum state. These runaways could break that requirement, though their physical role is unresolved. The work also offers a method that excludes a runaway for universes built from a circle and a sphere.
✦ The no-boundary model faces a specific test: whether its possible histories can stay mathematically controlled.