This is a bit off-topic for us, but creationists hate the Big Bang (it’s evidence-based and it isn’t scriptural) so that makes it a worthy (albeit very occasional) topic for us. We’ve posted a few times about creationists’ feelings on the subject, for example: Answers in Genesis and the Big Bang and also Creationists and Cosmology, Part 4.
In the world of science, the question of what existed before the Big Bang is somewhat murky, and understandably so. Until recently one popular idea was the oscillating universe, also known as the cyclic model. That describes the universe as an infinite series of Big Bangs, each of which is followed by a gravitationally caused Big Crunch, which would then go Bang again, ad infinitum.
We thought such speculation had fallen out of favor with the recent discovery that the observable rate of expansion of the universe is increasing (see accelerating universe), which seems to rule out a gravitational crunch, making the universe a one-time affair. If it’s not a unique event, then — here the speculation gets wild — we’re just one mote in an unimaginably huge multi-verse, so who knows what’s really going on out there. Those are by no means the only ideas floating around. Everyone in cosmology seems to have his own version. Lots of fun, although thin on evidence.
But now we have news of a new theory, and this seems to revive the oscillating universe idea. It’s by B. J. Carr (Astronomy Unit, Queen Mary University of London) and A.A. Coley (Department of Mathematics and Statistics, Dalhousie University, Halifax), and it’s published in arXiv.org: Persistence of black holes through a cosmological bounce. Here’s the paper in pdf format. The abstract says:
We discuss whether black holes could persist in a universe which recollapses and then bounces into a new expansion phase. Whether the bounce is of classical or quantum gravitational origin, such cosmological models are of great current interest. In particular, we investigate the mass range in which black holes might survive a bounce and ways of differentiating observationally between black holes formed just after and just before the last bounce. We also discuss the consequences of the universe going through a sequence of dimensional changes as it passes through a bounce.
This stuff is fascinating, but it’s not what we do and we won’t even pretend to make any knowledgeable comments. We’ll just give you a few excerpts, with bold font added by us. Here’s how it starts:
In some cosmological scenarios, the universe is expected to recollapse to a big crunch in the future and then bounce into a new expansion phase. The evidence that the universe is currently accelerating does not exclude this possibility if the acceleration is driven by a scalar field rather a cosmological constant. Even if the universe is destined to expand forever, its present expanding phase may have been preceded by the collapse and bounce of an earlier universe. Both past and future bounces would arise in cyclic models but not all bouncing models are cyclic.
We’re already lost, but let’s read on:
As regards the bounce mechanism, even classical general relativity (GR) permits a turn-around if one invokes a positive cosmological constant, although this simple option is not favoured by current observations. Other possible mechanisms are …
We’ll skip their description of the various mechanisms, but it’s nice to know there’s still a chance the universe may bounce, rather than expanding into ever more tenuous nothingness. (We’re toast either way, but somehow we find comfort in the thought that there would be another universe after this one.) The paper continues:
Whatever the scenario, black holes would be an important probe of a cosmological bounce, just as primordial black holes (PBHs) provide an important probe of the early stages of the standard big bang. However, the issues raised are somewhat different for future and past bounces. Both scenarios raise the question of whether black holes formed in one universe can persist into the next but the existence of a past bounce directly impinges on observations.
If you want to survive the Big Crunch, it looks like your best chance is to be a black hole. After a couple pages of math they discuss this:
One important observational issue is whether it is possible to differentiate between black holes formed just before and after the bounce.
Then they talk about this:
It is possible that the universe gains an extra spatial dimension — or goes through a sequence of dimensional increases — as it approaches the big bang in the past or the big crunch in the future.
After the authors conclude that there may be pre-bounce black holes, we are told:
The consequences of such black holes, only some of which have been discussed here, provide an important signature of bouncing cosmologies, which allows them to be falsified by observations.
We were lost when this began, and we’re still lost, but we enjoyed it anyway. Perhaps you will too.
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