An international team of physicists, led by Professor Enrique Gaztañaga from the University of Portsmouth's Institute of Cosmology and Gravitation , have challenged the concept that the Universe was started by the Big Bang.
In a new paper published in Physical Review D , the researchers propose a new model for the origin of the Universe - claiming that its formation is the result of a gravitational collapse that generated a massive black hole, followed by a 'bounce' inside, which means that our universe may have emerged from the interior of a black hole formed within a larger parent universe.
They are calling the new model the 'Black Hole Universe', offering a radically different view of cosmic origins which is grounded entirely in known physics and observations
The paper suggests that rather than the birth of the Universe being from nothing, it is the continuation of a cosmic cycle - one shaped by gravity, quantum mechanics, and the deep interconnections between them.
While the existing standard cosmological model, based on the Big Bang and cosmic inflation, has been successful in explaining the structure and evolution of the Universe, it leaves some fundamental questions unanswered.
Professor Gaztanaga said: "The Big Bang model begins with a point of infinite density where the laws of physics break down. This is a deep theoretical problem that suggests the beginning of the Universe is not fully understood.
"We've questioned that model and tackled questions from a different angle - by looking inward instead of outward. Instead of starting with an expanding Universe and asking how it began, we considered what happens when an overdensity of matter collapses under gravity."
What happens inside a black hole remains a mystery. In 1965, Roger Penrose proved that under very general conditions, gravitational collapse must lead to a singularity. This result, extended by Stephen Hawking and others, underpins the idea that singularities like the Big Bang are unavoidable. Singularity theories rely on classical physics but if quantum effects are included, as they would be in extreme densities, the story is likely to change.
Professor Gaztanaga continued: "We've shown that gravitational collapse does not have to end in a singularity and found that a collapsing cloud of matter can reach a high-density state and then bounce, rebounding outward into a new expanding phase.
"Crucially, this bounce occurs entirely within the framework of general relativity, combined with the basic principles of quantum mechanics. What emerges on the other side of the bounce is a Universe remarkably like our own. Even more surprisingly, the rebound naturally produces a phase of accelerated expansion driven not by a hypothetical field but by the physics of the bounce itself."
"We now have a fully worked-out solution that shows the bounce is not only possible - it's inevitable under the right conditions. One of the strengths of this model is that it makes predictions that can be thoroughly tested. And what's more this new model has also revealed that the Universe is slightly curved, like the surface of the Earth."
The Black Hole Universe model does more than fix technical problems with standard cosmology, it offers a new perspective on our place in the cosmos. Furthermore, it could also shed new light on other deep mysteries in our understanding of the early Universe - such as the origin of supermassive black holes, the nature of dark matter, or the formation and evolution of galaxies.
The ARRAKIHS ESA space mission, in which Professor Gaztanaga is the Science Coordinator, will be transformative in answering such questions and testing predictions.
ARRAKIHS is uniquely designed to detect ultra-low surface brightness structures in the outskirts of galaxies - regions where the fossil record of galaxy formation and dark matter assembly is preserved. These faint features are essential for studying how galaxies grow and evolve, but may also hold clues to the nature of dark matter and the universe's initial conditions, particularly if they differ from those predicted by the standard Big Bang model.
The ARRAKIHS satellite is equipped with four wide-angle telescopes that observe simultaniously the same region of sky: two using cutting-edge near-infrared technology, one optical, and one covering the near-ultraviolet. The ICG has been responsible for proposing and defining this revolutionary filter system. Together, they can detect signs of star formation and black hole accretion. These unique space-based capabilities can not be achieved from ground based observations and will allow the formation history of galaxies, like our own Milky Way, to be unveiled.
The international team led by Professor Gaztanaga comprised Sravan Kumar and Swaraj Pradhan, both also from the University of Portsmouth, and Michael Gabler from the Universitat de Valencia (Departmento de Astronomia y Astrofisica), Valencia, Spain.
Professor Gaztanaga is also a Professor at the Institute of Space Sciences (CSIC/IEEC) in Barcelona and publishes a science blog called Dark Cosmos .
