We all know that everything kicked off when the Big Bang exploded our universe into reality, right? Well, not necessarily.
A compelling new theory of the creation of our universe suggests that it may not have first begun merely as the single violent paroxysm we are all familiar with, but instead the big bang was actually a rebound from an earlier contraction.
This earlier, massive gravitational collapse would have effectively condensed a former universe of galaxies into an infinitesimally small, massively hot, and extremely dense nugget of negligibility – far smaller than an atom – known as a singularity.
When this potential collapse occurred, it would have sucked almost everything in, but may have left some former black holes that have survived into the present day as “cosmic fossils”, a team of scientists from the UK’s University of Portsmouth’s Institute of Cosmology and Gravitation and the Institute of Space Sciences in Barcelona, have suggested.
Their research, published in the journal Physical Review D, hypothesises that when the big bang detonated, creating the rapidly expanding universe we all know and love, these remnant black holes then became some part of the fabric of our universe.
“If this theory is correct, these primordial space objects could help explain several long-standing mysteries in cosmology, including the nature of dark matter and the processes that seeded the formation of galaxies,” the team said.
This theory of a universe created on the rebound is tentatively known as “the black hole universe”.
Professor Enrique Gaztañaga, lead author of the study said: “For almost a century, cosmologists have traced the history of the universe back to a single dramatic moment known as the big bang. In the standard picture, space and time emerged from an extremely hot, dense state around 13.8 billion years ago, followed by billions of years of cosmic expansion and galaxy formation.
“This model has been remarkably successful. It explains the cosmic microwave background – the faint radiation left over from the early universe – and accurately predicts how galaxies are distributed across vast cosmic distances.
“But some of the deepest mysteries in physics remain unresolved. We still don’t know what triggered the big bang, why the universe began in such a special state, what caused the brief burst of rapid expansion known as inflation, or what the invisible ‘dark matter’ is that outweighs ordinary matter by about five to one.”
He added: “Our research explores a possibility that could connect several of these puzzles: the universe may not have begun with a singular bang at all, but instead emerged from a cosmic bounce mimicking inflation, with some of the oldest objects in the universe potentially surviving as relics from before it.”
The team believe that in this theoretical scenario, some black holes could have formed during the earlier cosmic phase and then survived the bounce, leaving behind relic objects that may still influence the structure of galaxies billions of years later.
Other black holes could have then formed shortly after the bounce, due to “amplified density fluctuations”, which occur because matter in the early universe was unevenly distributed in stronger, “more pronounced clumps than usual”.
“These clumps of matter would then collapse more easily under their own gravity, making it more likely for large cosmic structures (and black holes) to form early on,” the team said.
One of the key frustrations physicists today have with Einstein’s general theory of relativity regards singularities – the points at the centre of black holes or the point at which the big bang erupted from.
This is because they represent a breakdown of the theory itself. It fails to describe how density becomes infinite and the known laws of physics break down. Many physicists therefore interpret this as a sign that our current description of the earliest moments of the universe is incomplete.
Instead of collapsing into an infinite singularity – a problematic theory – the new theory suggests universe instead collapses to a very high, but finite, density before reversing this motion in an explosive expansion.
Professor Gaztañaga added: “Singularities often signal that our theoretical description has reached its limits. A bounce provides a way for the universe to transition from contraction to expansion without requiring new exotic physics.”
Importantly, the team’s calculations suggest “compact objects larger than roughly 90 metres in size could pass through the transition and reappear in the expanding Universe as fossils from before”.
As well as black holes, possible other relics include gravitational waves and density fluctuations, they said.
“These relic black holes could help explain dark matter, the invisible substance that shapes galaxies and the large-scale structure of the universe. If large numbers formed during the bounce, they could make up a significant fraction – potentially even all – of dark matter,” Professor Gaztañaga said.
“If massive black holes already existed immediately after the bounce, the early universe would not need to start from scratch when building the first galaxies,” he added.
The team has proposed tests which could help indicate if the theory holds water or if there are holes in it. These include astronomers identifying relic gravitational waves from a previous cosmic phase, or “subtle patterns in the cosmic microwave background that preserve traces of the universe before the big bang”, they said.
Professor Gaztañaga added: “If the universe did experience a bounce, the dark structures shaping galaxies today could be remnants from a cosmic epoch that preceded the big bang.”