Review of the No-Boundary Wave Function

Understand

When the universe is treated as a quantum system, it is described by a wave function.

• This wave function is a function not only of the matter fields, but also of spacetime.
• The no-boundary proposal is the idea that the wave function should be calculated by summing over geometries that have no boundary to the past, and over regular matter configurations on these geometries.
• Accordingly, the universe is finite, self-contained and the big bang singularity is avoided.