Suppose the birth of the universe was not a definite start, but a cosmological rebound far within a black hole? This radical idea has been picking up steam as new theoretical research, spearheaded by Enrique Gaztanaga at Portsmouth University, provides an alternative account of how it all began. The new theory, which appeared in Physical Review D, suggests that the Big Bang was not an event in a vacuum, but the echo of a collapse into a black hole within a larger, older universe.
Underlying this theory is a discomfort with the familiar cosmological model’s dependence on singularities locations of infinite density where the rules of physics fail. “This is not just a technical glitch; it’s a deep theoretical problem that suggests we don’t really understand the beginning at all,” Gaztanaga explained in an essay for The Conversation. The standard model, although successful in the explanation of cosmic microwave background radiation and the large-scale structure of the universe, relies on unobservable entities such as inflationary fields and dark energy to explain the universe’s accelerating expansion and its high degree of uniformity.
Gaztanaga’s model flips the problem inside out literally. Rather than tracing the expansion of the universe backward to an unexplainable singularity, the theory asks what occurs when a dense cloud of material is compressed by gravity. Traditional general relativity, demonstrated by Roger Penrose and Stephen Hawking, predicts that such collapse inevitably results in a singularity. But those theorems are based on classical physics, which leaves out quantum effects that become important at high densities.
The new model brings quantum mechanics into the mix, specifically the quantum exclusion principle, which prevents identical fermions from sharing the same quantum state. It is this principle, which is accountable for the stability of neutron stars and white dwarfs, that applies a pressure that resists compressing to infinity. “This principle creates a kind of pressure called degeneracy pressure that resists compression. It’s what stops the cores of dying stars from collapsing endlessly, and it’s what can trigger a supernova explosion. In our model, it’s this same quantum effect that halts the universe’s collapse and causes it to bounce,” Gaztanaga told Space.com.
Mathematically, the group derived an exact analytical solution: as the universe heads toward the would-be singularity, its size varies as a hyperbolic function of cosmic time, contracting to a minimum before expanding again outward. The result is a universe that naturally displays both early cosmic inflation and the existing dark-energy–powered expansion without the need for hypothetical new fields. “Even more surprisingly, the rebound naturally produces the two separate phases of accelerated expansion – inflation and dark energy – driven not by hypothetical fields but by the physics of the bounce itself,” Gaztanaga wrote for The Conversation.
This method harmonizes with recent work in Loop Quantum Cosmology (LQC), a model that uses quantum gravity in cosmological models. LQC substitutes the classical singularity with a quantum bounce, providing a non-singular evolution for the universe. The bounce cosmology in LQC has been researched in detail, where authors like Abhay Ashtekar and Martin Bojowald have shown that the effects of quantum gravity can avert the infinite curvature of general relativity. The models also indicate that the evolution of the universe is described by difference equations rather than differential ones and that quantum corrections may imprint themselves on the cosmic microwave background or the creation of primordial black holes.
The model of the bounce off a black hole also predicts something testable. It predicts a minute but non-vanishing positive curvature of space, a faint remnant of the original overdensity that caused the collapse. If such a curvature is found by missions such as ESA’s ARRAKIHS, intended to chart the dark matter’s invisible structures and the diffuse halos of galaxies, that would be robust proof for the bounce model. The model also predicts the presence of relic compact objects, like primordial black holes or neutron stars, created prior to the bounce and possibly accessible to next-generation telescopes.
The latest discoveries from the James Webb Space Telescope add another twist to the story. Observations have demonstrated a preferred axis in the spin of early galaxies, an effect that would be explained naturally if our universe inherited its axis from a parent rotating black hole. As theoretical physicist Nikodem Poplawski explained to Space.com, “A preferred axis in our universe, inherited by the axis of rotation of its parent black hole, might have influenced the rotation dynamics of galaxies, creating the observed clockwise-counterclockwise asymmetry.”
Though the black hole bounce model is still contentious, it is well based in known physics merging general relativity and quantum mechanics without invoking untested new fields or dimensions. As Gaztanaga pointed out, “Challenging long-held assumptions is essential to scientific progress.” With future missions on the horizon to seek out the universe’s greatest secrets, whether our universe began with a bang or a bounce remains one of the most intriguing in contemporary science.
