The birth and ultimate fate of the 13.7 billion year old universe is a subject that has intrigued scientists since the dawn of civilization. We know that the universe is expanding, although there is a disagreement over how fast. We also know that the universe can only expand so far, and that ultimately, it will slow its expansion. However, there is no consensus on what happens after. Two Argentine cosmologists, Daniela Pérez and Gustavo Romero of the Instituto Argentino de Radioastronomía, have a developed a new theory, which suggests that the universe is in a permanent state of expansion and contraction, a “cosmological bounce” whose only survivors are black holes. 

Indestructible Black Holes

Pérez and Romero investigated whether a black hole can exist and survive in a universe defined by cosmological bounces. Their study was done through a “central inhomogeneity embedded in a bouncing cosmological background modeled by the comoving generalized McVittie metric”. What they found was startling. They found that a dynamical black hole can indeed exist and survive throughout all cosmological epochs. So, black holes that survive a cosmic collapse may play a role in the following expansion phase. It is an incredible finding. This seeming indestructibility of black holes is, on its own, a big deal. 

However, for this theory to be correct, a range of assumptions have to hold true. While the hard sciences are the most advanced field of empirical-based knowledge we have, there is still a lot that we don't know. We don’t know if the physics we use in this expansion phase will hold when the universe bounces to a contraction phase. We already know that general relativity is not universally applicable, breaking down at black hole and cosmological bounce singularity. The biggest assumption that the paper makes is that there is no change in physics during a cosmological bounce. That’s a hard sell. In the face of singularity, how would black holes behave? 

Cosmological Bounces and Other Theories of the Universe

Pérez and Romero’s contribution is not the notion of cosmological bounces, it is this idea that black holes are indestructible in the face of them. Cosmological bounces are widely held to be the likely progression of the universe. One group of scientists estimates that the universe is reaching the end of this expansion phase, with a contraction phase due in a hundred or so million years, before the next cosmological bounce several or tens of billions of years later.

There are competing theories about the fate of the world. It may, according to some, slow down and freeze, before collapsing in on itself or breaking apart with pieces spinning away to form smaller universes. 

The theory of cosmological bounces is important because it ties together all the weird bits of science that we know and which we struggle to make sense of. For instance, the universe is a vast expanse of nothingness with these hard objects dotted across it: stars, galaxies, planets, and on earth, people. This makes sense in a universe defined by cosmological bounces, because we can explain them as by products of these periods of expansion and contraction. 

Black Holes in the Scientific Imagination

Black holes, especially supermassive black holes, are explicable in a universe defined by cosmological bounces. Black holes have fascinated scientists since they were first observed and telescopes such as the Event Horizon Telescope (EHT) have discovered numerous black holes. 

Black holes are near-singularities, because they defy known physics. It is there that known physics breaks down. They are vast, dense entities that destroy even light. We know very little about them. They remain a mystery, and the mysteries behind black holes may be the secret that allows them to survive across all cosmological phases, while everything else is smushed up into a peanut butter made of energy and matter. 

Pérez and Romero’s fascination with black holes is a testament to the mysteries they continue to withhold from us. They may be right and black holes are indestructible entities that survive across all cosmological phases, and which are crucial to the very ability of the universe to bounce from one phase to another.

Pérez and Romero believe that black holes feed the universe with expanding matter, mixing it with energy after a cosmological bounce. By surviving a bounce, black holes are able to give rise to what they call, “perturbations”, that generate structure and form galaxies. Black holes, rather than just being these dark beasts that suck in all life, are also creative engines, making and remaking the stars, galaxies and planets. 

Supermassive black holes have been proposed but not observed. Their existence would dovetail with Pérez and Romero’s theory. Pérez and Romero aren’t the first cosmologists to believe that black holes can survive cosmological bounces. For instance, Barnard Carr, Timothy Clifton, and Alan Coley developed models that showed that black holes could survive cosmological bounces. The key difference is that Pérez and Romero believe that black holes are embedded in the contracting universe’s structure, rather than just being inside of it.