Our Universe Could Have Begun Inside a Black Hole — The Quantum "Gravitational Bounce" Explained

Could the Big Bang Have Been a Bounce?

The Big Bang has been the prevailing account of cosmic origins for nearly a century: a moment when space, time and energy emerged from an extremely dense state. A team led by Professor Enrique Gaztañaga at the Institute of Cosmology and Gravitation, University of Portsmouth, proposes a concrete alternative in a paper published in Physical Review D. Their gravitational bounce scenario replaces the notion of a singular beginning with a continuous process in which collapse is followed by rebirth.

How the Black Hole Universe Model Works

In this model, our observable universe could be the interior of a massive black hole that formed inside a larger “parent” universe. As matter falls inward during collapse, quantum mechanics prevents all particles from occupying identical states. That resistance — the same degeneracy pressure that supports white dwarfs and neutron stars — grows strong enough to halt collapse before an infinite-density singularity forms.

When compression reaches a critical density, the effective pressure can become negative in the model’s equation of state. That negative pressure drives a rapid outward expansion that behaves like the inflationary phase inferred from cosmic observations. The trapped energy inside the black hole then rebounds, creating a new, separate region of spacetime — effectively a new universe.

Gaztañaga: “We look in, rather than out. Gravitational collapse does not have to end in a singularity.”

Key Predictions and Numerical Results

The authors report that numerical models give an inflationary e-fold of roughly ≈ 57, a value consistent with measurements of the cosmic microwave background by the Planck satellite. They also derive a small global curvature for our universe and quote a value near −0.07 ± 0.02. (Note: different curvature conventions exist in cosmology; the authors’ numerical sign should be interpreted with the convention they use.)

Observational Tests

A major strength of the proposal is its testability. Gaztañaga is science coordinator for ARRAKIHS, a planned European Space Agency mission that will use four wide-angle telescopes (two near-infrared, one optical, one near-ultraviolet) to probe the faint outer regions — the halos — of galaxies. Those outskirts preserve a "fossil record" of galaxy formation that could retain subtle imprints of the early universe’s physics.

If the cosmos experienced a gravitational bounce rather than a singular explosion, tiny deviations from standard inflationary predictions might survive in galaxy halos or in large-scale structure. Future surveys could therefore provide empirical evidence for—or against—this scenario.

Implications and Caveats

The Black Hole Universe model does not invoke new exotic particles or untested forces: it relies on quantum degeneracy pressure combined with general relativity. If supported by observations, the model would remove singularities from both black hole interiors and cosmic origins, recasting the Big Bang as a transition event — a smooth bounce following collapse in a parent cosmos.

However, the idea remains a theoretical proposal that depends on details of quantum gravity and matter at extreme densities. Independent analyses, alternative models, and precise observational tests will be needed to assess whether this scenario can fully replace or complement standard inflationary cosmology.

Why This Matters

The proposal offers a conceptually economical link between physics we already observe in dense stellar objects and the origin of the universe. It opens a potentially falsifiable route to reconcile aspects of quantum mechanics and gravity and suggests new observational strategies to probe cosmic origins.

Reference: Gaztañaga et al., Physical Review D. The paper and supporting materials are available online.