An international team of physicists led by Professor Enrique Gaztañaga of the Institute of Cosmology and Gravitation at the University of Portsmouth has questioned the idea that the Universe began with the Big Bang. In an article published in Physical Review D, the researchers propose an alternative model for the origin of the cosmos, explaining that its formation could be the result of a gravitational collapse that generated a massive black hole, followed by a “bounce” within it. According to this theory, our Universe would have emerged from inside a black hole created in a larger, earlier universe.

This new model, called the Black Hole Universe, offers a radically different perspective on cosmic origins, based on already known physical principles and concrete observations. Unlike the Big Bang theory, which posits a beginning from a singularity of infinite density, this approach suggests that the Universe was not born from nothing but is part of a cosmic cycle shaped by gravity, quantum mechanics, and their intricate interplay.

The standard cosmological model, based on the Big Bang and cosmic inflation, explains the structure and evolution of the Universe but leaves fundamental questions unresolved. The Big Bang model starts from a point of infinite density where the laws of physics break down, explained Professor Gaztañaga. This represents a profound theoretical problem indicating that the origin of the Universe is still not fully understood.

Faced with this limitation, the team decided to approach the enigma from another angle. Instead of starting from an expanding Universe and asking how it began, we asked what happens when an overdensity of matter collapses under its own gravity, said Gaztañaga.

origin universe big bang previous
The expansion of the universe since the Big Bang. Credit: Public domain / Wikimedia Commons

The Mystery of Black Holes and the “Quantum Bounce”

What happens inside a black hole remains one of the greatest mysteries in physics. In 1965, Roger Penrose showed that under very general conditions, a gravitational collapse inevitably leads to a singularity. This result, later expanded by Stephen Hawking and others, reinforced the idea that singularities like the one in the Big Bang are inevitable. But these theories are based on classical physics; if quantum effects—unavoidable under extreme density conditions—are introduced, the picture changes completely.

We showed that gravitational collapse doesn’t have to end in a singularity, said Gaztañaga. We found that a collapsing cloud of matter can reach a state of high density and then bounce, expanding again into a new phase of expansion. This phenomenon, known as a quantum bounce, occurs within the framework of general relativity combined with basic principles of quantum mechanics.

Most surprisingly, according to the researchers, what emerges after the bounce is a Universe very similar to ours. The bounce naturally produces a phase of accelerated expansion, driven not by a hypothetical field like dark energy, but by the physics of the bounce itself, explained Gaztañaga.

Testable Predictions and a Slightly Curved Universe

One of the greatest strengths of this Black Hole Universe model is that it offers predictions that can be tested experimentally. Among them, the team discovered that the Universe could have a slight curvature similar to the surface of the Earth, a finding that contrasts with the traditional view of a flat cosmos, dominant in the Big Bang theory.

In addition to solving technical problems of the standard cosmology, this model opens new perspectives on our place in the cosmos and could explain other mysteries such as the origin of supermassive black holes, the nature of dark matter, or the formation of galaxies.

To test these predictions, Professor Gaztañaga and his team rely on the ARRAKIHS space mission from the European Space Agency (ESA), in which Gaztañaga serves as scientific coordinator. Designed to detect ultra-low surface brightness structures in the outer regions of galaxies—areas where the fossil record of their formation is preserved—ARRAKIHS could provide crucial data on the initial conditions of the Universe, especially if they differ from those predicted by the Big Bang model.

The ARRAKIHS satellite is equipped with four wide-angle telescopes that simultaneously observe the same region of the sky: two operate in the near-infrared, one in the optical spectrum, and another in the near-ultraviolet. This revolutionary system, proposed and defined by the Institute of Cosmology and Gravitation in Portsmouth, will allow for the detection of signals of star formation and black hole accretion with a level of precision impossible to achieve from ground-based observatories.

SOURCES

University of Portsmouth

Enrique Gaztañaga, K. Sravan Kumar et al., Gravitational bounce from the quantum exclusion principle. Physical Review D, 111, 103537 – Published 29 May, 2025. DOI:doi.org/10.1103/PhysRevD.111.103537

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