Universe Without a Beginning: Quantum Cosmology Confirms Hawking's Idea express
The birth of the Universe is usually associated with the Big Bang — a point of infinite density. But at that point, the laws of physics break down, which bothers scientists. Stephen Hawking and James Hartle back in the 1980s proposed a different view: time has no boundary, like the surface of a globe. The Universe simply exists, and the question 'what was before the beginning' loses its meaning.
For a long time, probability calculations in this model were incomplete. The rules of the quantum world require not just enumerating possible outcomes, but correctly summing their chances, avoiding illusions. When physicists finally carried out these correct computations, it turned out: almost any closed world has no beginning. The probability of finding ourselves in such a universe is almost 100%.
Moreover, under a special statistical approach, this probability becomes exactly one. Such a result naturally explains the rapid expansion at the dawn of existence — inflation arises without fine-tuning.
Original abstract
as written by the authors arXiv:2602.02682
We revisit the Hartle-Hawking no-boundary proposal. To extract probabilities, one must use the gravitational path integral (GPI) to compute not only the no-boundary amplitude, but also the norms by which its square is divided. We find that this dramatically alters predictions: the probability for any closed universe is either nearly 1, or exactly 1. That is, in the Hilbert space of closed universes defined by the GPI, the states of interest in cosmology are all nearly parallel to the Hartle-Hawking state up to nonperturbative corrections in $$G_N^{-1}$$. We also consider a statistical interpretation of the GPI, as an average of arbitrary products of amplitudes. We find that all amplitudes are exactly 1 in this case, consistent with recent arguments that the statistical approach to the GPI with a closed boundary computes an average over one-dimensional Hilbert spaces. As an example, we illustrate the consistent evaluation of the no-boundary proposal in inflationary cosmology.
Hawking liked to compare the question 'what was before the Big Bang' to 'what is south of the South Pole.' If time is closed, both are meaningless.