You exist somewhere on Planet Earth, which orbits a rather average star we call the Sun, which in turn orbits around the centre of the Milky Way Galaxy which is but one of billions and billions of galaxies within our observable Universe. That’s what you’d include in any description of your reality.
However, perhaps the observable Universe itself exists within a Black Hole (hereafter BH). That’s an alternative reality, or at least an extension of your reality. Just what rationale might lead one to suggest that our observable Universe and a BH could be in parallel?
Since you cannot escape from the universitycafe prison we call the Universe; and since you could not escape from the inside of a BH – another type prison – perhaps they are one and the same sort of prison. Perhaps not only do BH’s exist inside our Universe but the Universe itself resides inside a BH with perhaps no end of the inside-the-inside-the-inside in either direction. In a manner of speaking, that’s a Multiverse!
Actually you can in theory escape this Universe by hopping down into a BH, but if, and it’s a very big ‘but if’, you survive, you’ve just traded in one maximum security prison for another.
Let’s explore this concept a little further and see where, if anywhere, it leads us.
Our Universe and BH’s certainly share some things in common.
A BH can expand and surprisingly contract (due to Hawking radiation; the technicalities need not concern us here). Our Universe is expanding, but in theory could also contract if there was enough stuff, matter, hence gravity to slow down the expansion to an eventual halt hence reverse direction and start to shrink.
A BH has temperature (that Hawking radiation); our Universe has a temperature (the cosmic background microwave radiation).
A BH has mass (hence gravity); our Universe has mass (hence gravity).
A BH could have a net charge; our Universe could have an excess of one kind of charge over another, but to the best of our knowledge our Universe is electrically neutral, and we suspect, so might an average BH be too.
A BH may be spinning; our Universe maybe rotating but the only way of knowing if you are rotating is if something else in your line of sight isn’t rotating or rotating at a different rate. If everything in our Universe is rotating together at the same rate, then there’s no way of telling since there isn’t anything else to relate that rotation to.
Now the question arises was there a prime cause; a first universe inside a BH that gave birth to millions more BH’s each of which generated an interior universe each of which spawned million more BH’s hence interior universes and so on and so on and so on. It’s all very circular in that BH’s generate universes which generate more BH’s which generate more universes, etc. But that is something circular in a very linear sort of way for what you end up with is like an ongoing (maybe infinite) series of funnels. Sooner or later all the stuff that existed in the first cause BH universe will funnel down into the first generation of BH universes and all the stuff there eventually finds its way down into the second generation of BH universes, hence funnelled down to the third, and fourth and down unto infinity. Now the point here is that there was only a finite amount of stuff (matter/energy) in that first cause BH universe. All that stuff is constantly being diluted as one passes from one generation to the next generation. The stuff of the prime cause first BH universe is dispersed unto millions and eventually billions of later universes. Eventually every baby universe in some umpteenth generation of universes would be so dilute no further BH’s could form and that’s then the end of that.
But, what if things were cyclic or really circular? All of these universes do not exist in separate and apart timeframes, just like great grandpa; grandpa; father and son do not of necessity exist in separate and apart timeframes but can co-exist at the same time. When you talk of BH’s, you can also go the one yard further and talk wormholes, which I guess is really that passageway from a BH to the baby universe it generated. But if that first BH universe generates say a million BH’s each generating a baby universe, what’s to say that a BH created in that baby universe might not funnel back stuff, not to a newer next generation, but dump their contents back to the original first cause BH universe. Wormholes can, in theory, under the right conditions, serve as time machines. So it’s almost akin as if the son travelled back in time and fathered what would ultimately become his great grandpa. Cyclic! If cyclic, the amount of stuff (matter/energy) is still fixed (that which existed in the original BH universe), but never gets diluted enough to bring things to a halt. Now about those quasars, gamma ray bursts and related ultra-energetic astronomical enigmas – White Holes perhaps; the exit of the BH entrance – impregnations by those baby universe BH’s?
Where actually do these new (and improved?) baby universes reside? I doubt that a BH opens up a portal and creates a never-before-in-existence arena of space-time where stuff pouring into a BH, hence exiting this portal, finds a ready made newly constructed house to live and evolve in. Rather, the baby universe IS the interior of a BH. A BH forms, a new baby universe forms inside that BH, and that universe in turn produces new BH’s that form new baby universes, etc. But everything takes place, generation after generation, inside that first BH (which just might be our Universe). The baby universes spawned inside say BH generation #3 in turn creates BH generation #4 which also exist within the earlier BH generation #3 as do the generation #4 baby universes. So instead of a series of dolls sitting all-in-a-row on a long shelf, it’s more akin to those Russian dolls, one inside the other inside the other inside the other. But, as suggested above, one of the smaller dolls can ultimately funnel stuff back up into one of the larger dolls.
Aside #1: Now you may feel that any baby universe inside a BH in our Universe is going to be a pretty small universe indeed. Well I’m not aware that the definition of a universe comes attached with a one size fits all clause. Universes might well come is small, medium, large and extra-large sizes. Maybe a baby universe inside a BH is like Dr. Who’s TARDIS – bigger on the inside than on the outside. Truth is, nobody, and I do mean nobody has a clue what’s inside the event horizon of a BH. Once inside the event horizon all the laws, principles and relationships of physics break down. Nobody and no measuring instrument have ever been inside to have a look at what’s what and report back. It’s akin to those maritime charts of the ancient seafarers – here be dragons! It’s the greatest of the great unknowns. If space is the final frontier, the inside of a BH is the Absolutely Final Frontier. Now there’s no reason of necessity why any of these baby universes need be inhabited. Extraterrestrial intelligence isn’t part of the definition of a universe either. A universe is really a self-contained space where matter and energy interact; where things happen; where there is change from moment to moment. The interior of a BH is self-contained. There’s matter and energy but whether there’s activity or not, well IMHO the answer is affirmative since the BH isn’t static. It’s either expanding as matter and energy enters and passes the event horizon or contracting thanks to the abovementioned Hawking radiation. Actually both incoming and outgoing are going on simultaneously.
Aside #2: Something about this entire concept reminds me of the old sci-fi pulp magazine era. It was a staple plot of shrinking down to the atomic level only to discover a civilization on a ‘planetary’ electron orbiting a ‘stellar’ nucleus.
Aside #3: A BH that might spew out another universe might have that universe stillborn in that that universe may not in turn be able to give rise to internally created BH’s and thus another generation of baby universes. Not all universes will of necessity have the same physics, physics that allow the creation of BH’s, and so some universes will be eternal bachelors or spinsters.
Aside #4: Yet another interesting question is what happens to the two baby universes when and if their parent BH’s merge, as most certainly can happen. That would seem to be a rather nasty scenario for inhabitants of either of the baby universes!
Now clearly this is all speculation, but then speculation, that “what if” scenario, is the bread-and-butter staple of science fiction, and how often has science fiction evolved into science fact? It’s an oft quoted saying, attributed to J. B. S. Haldane (1924) that “The Universe is not only queerer than we suppose, but queerer than we can suppose.”