It all starts with a tiny scar — a thin tunnel connecting two universes. In quantum cosmology, there has long been discussion that our closed universe could have been born from "nothing" via tunneling (a process where a system overcomes a barrier that is insurmountable by ordinary standards). But what if it's not quite "nothing," but rather a trace left after detaching from a parent universe?

In the new work, scientists propose a "small throat recipe." They describe the birth of the universe not as appearing from a point, but as pinching off from a parent universe through a thin tunnel. To avoid wrestling with the full geometry, the authors take a simplified model of a closed universe with a positive cosmological constant (the energy of empty space that pushes space apart) and add a tiny portion of radiation. This addition creates two turning points: an inner one very close to zero, and an outer one as large as the future size of the universe. By imposing special conditions on the initial size, the authors cut off unwanted solutions and single out the tunneling branch. When the addition tends to zero, their recipe smoothly transitions into the standard "from nothing" tunneling.

This approach bridges two competing ideas: the tunneling wave function proposed by Alexander Vilenkin, and the no-boundary wave function of James Hartle and Stephen Hawking. It turns out that the choice of how to describe time in the path integral can yield either growing branches (as in Hartle–Hawking) or tunneling ones. The tiny throat becomes the bridge that allows one to transition from one description to the other without resorting to mysterious boundary conditions at zero size.