One of my students sent me an interesting email earlier tonight. I'm not sure that my reply was what they were expecting, but I hope they found it interesting. I've posted it below in the hope that you might find it interesting, too.
This email is merely out of curiosity.
I was reading a rather interesting article today about black holes. It was related to the Big Bang Theory, and I was curious about how much store you would put by it. It mentions that the majority of scientists refer to black holes as the 'ultimate Fort Knox' and impenetrable; 'we will never know what its inside a singularity'. This, I thought, was quite true until I read further and found myself quite partial to the ideas of some 'unorthodox' (how the article referred to them as) thinkers, who believe that its becoming increasingly accepted that our universe is not all there is. They defined where we live as a 'multiverse' - a vast collection of universes in the Swiss cheese of reality.
I found this quite interesting, that it is speculated that it is possible to give birth to a new universe through taking matter from another universe, crunching it down and sealing it off - like what a black hole is thought to do. The article goes on to explain how this relates to the Big Bang Theory:
"We do know, after all, what became of at least one singularity. Our universe began, 13.8 billion years ago, in a tremendous big bang. The moment before, everything was packed into an infinitesimally small, massively dense speck - a singularity."
I believe that this is insinuating that the matter of our universe came into being from being crushed matter dragged through a black hole from another universe?
I find this to be very interesting, and out of curiosity, would like to know your opinion. Do you know of this theory? Do you believe it?
What a fascinating question!
I am very much aware of multiverse theory, though I don't recall ever seeing it explained in quite that fashion. I've spent quite a lot of time recently looking into the mysteries of black holes and singularities, as one of my Year 13 students is writing his Extended Project Qualification on them! Singularities, if you'll forgive the pun, are a singular oddity in Physics: we're almost certain that they exist, but we don't have the Physics to describe what they are like, beyond a certain point.
The idea of a black hole has fascinated me for decades: at once both a definable and yet undefinable region in space, with an event horizon, beyond which you cannot observe, and where the normal laws of time, space, energy and reality break down as they get crushed into a zero-dimensional point of infinite density. In the classical and relativistic view (of Einstein) the singularity of a black hole is an enigma, where time and space are warped so violently by the black hole that not even light can escape and as you approach the singularity itself and pass beyond the event horizon (the limit of where you can observe what is going on as you approach the black hole) observable time slows down and even stops at the instant the object you observe meets the event horizon; a ravening monster of physics from which nothing escapes, consuming all matter which dares approach, consigned to a fate of who-knows-what? The modern, quantum-mechanical view of a black hole is even more bizarre - a maelstrom of space-time weirdness whose tidal forces stretch approaching matter like strands of spaghetti, where the space surrounding the event horizon incinerates all matter unfortunate enough to be grasped by its gravitational clutches in a searing firewall of quantum information, and where the event horizon "leaks" Hawking radiation and causing the black hole to gradually lose its mass through mass-energy equivalence "evaporation".
Beyond the event horizon, within the singularity itself, it's probably fair to say that no-one really understands what goes on in there. Once you get inside the event horizon of a black hole, all the equations that describe how matter, energy and forces (including gravity) work in "real" space completely break down and profoundly weird things start to happen - if you try on your calculator to take the square root of a negative number, your calculator will probably go "Nope. Not happening, pal!", because the answer is what mathematicians call an "imaginary number"; That is, the square root of -1 is i. To describe what goes on inside the singularity of a black hole require a time expressed in these imaginary numbers. This is quite a challenging concept to get your head around! Even worse, when you try and figure out what is going on in the spacial dimensions of the singularity, things also get "imaginary", meaning that you can no longer make any distinction between the dimensions of space and time when you get inside the singularity. This, also, is quite a challenging concept! (Hence the "ultimate Fort Knox" comparison!)
Since black holes were officially theorised following the publication of Einstein's Theories of Relativity a hundred years ago, plenty of scientists have tried to come up with theories as to what happens within the singularity itself - and pretty much all of them remain exactly that - theories. This is mainly because it is impossible to "prove" any physical theory - the best you can do is find evidence that fails to disprove the theory. The problem with trying to find evidence for what goes on inside the event horizon of a black hole is that it is, by its very nature, unobserveable though direct means, and secondly, getting close enough to a sufficiently large black hole to make any meaningful observations would be rather hazardous! The best we can do is make indirect observations of supermassive black holes (such as the ones at the centres of galaxies), which are active enough (that is, have enough stellar matter falling into them) for us to try and infer what is going on as matter approaches and crosses into the singularity.
One of the many theories is that as "what goes up, must come down" therefore "what goes in, must come out" - that as black holes gobble matter in from one end, "white holes" must regurgitate matter back into the universe somewhere else to preserve the law of conservation of mass-energy. It's an elegant idea (and one that links to the idea of matter being crushed up in one universe to be spilled out in another), but as pretty an idea as it is, white holes have never been observed in our universe. Likewise, theorists have also postulated that black holes may warp space-time so much that they form wormholes into the past and/or future. But again, we haven't observed any - so without any observable evidence, it simply remains yet another pretty, elegant theory.
My problem with multiverse theories is that they are, for all intents and purposes, fundamentally untestable. How can you test for the existence of a realm that may exist completely beyond the presently definable structure of reality? The mulitverse theory may very well be true, but if you can't find proof for it, what does it matter? It's like trying to answer the question "What happened before the Big Bang?" - the question itself (from a certain point of view) is fundamentally flawed, because our current understanding of the dimension of time is inextricably linked to the instant that the Big Bang occurred - there was no "before" because time, as we are capable of thinking about and understanding it, simply did not exist until the Big Bang occurred. (At this point it would probably be unhelpful to point out that "time" may not even be a fundamental dimension of the universe, given that there is no such thing as an "absolute" time!)
For me, a far more interesting question is "Why did the Big Bang happen?" Again, there are many theories - I'm not sure I buy the theory that the Big Bang was the result of matter being pulled into a black hole in another universe. The mass-energy requirements don't seem to stack up - if every black hole in our universe lead to the creation of another universe, those other universes would have to get recursively smaller and smaller to preserve the law of mass-energy conservation - a cosmic case of diminishing returns - and I'm not sure I like that idea; especially when you start factoring in potential "end of the universe" scenarios - how would the end of a "parent" universe affect the "daughter" universes? One of the more interesting theories is that each individual universe within the multiverse exists on a ten or eleven dimensional "brane" (like a membrane tissue floating in hyperspace) and that whenever these "branes" intersect in hyperspace, you get a Big Bang-like event that spawns matter and energy into the "brane". Again, very nice idea, but how do you test it? Though I suppose that my favourite multiverse theory is the deterministic universe, where each decision or event that occurs forms a branch point in space-time and there is an infinity of parallel universes where you get to play out the different consequences of every possible alternative to every decision you make throughout the course of your life. It's probably completely implausible from the perspective of conservation of mass-energy (where would all the mass-energy come from to create the infinity of parallel universes needed to satisfy the infinity of outcomes from an infinity of events?), but it does create the scope for some great science-fiction writing!
Finally, it's probably worth noting that not everyone actually accepts the Big Bang theory - and this is where the science veers dangerously towards philosophy, and perhaps, even theology. Some people don't like the idea of the Big Bang (and the single universe theory) because any event that implies a defined beginning to the universe also implies that the universe can end. Some people find that idea psychologically unsettling and much prefer the idea that the universe has always been here and will always be here. It's psychologically much more comforting to think that the universe is eternal and that there won't be an ultimate end to everything that has ever been and ever will be. Of course, I don't buy that idea either - I'm quite happy with the idea that the universe is all there is and all there will be, and that one day it might all come to an end (though what that end might be, well, that's a whole other question!), at least until someone finds some concrete evidence otherwise!