An interesting, but totally unsupported, theory is that “existence” is composed of an infinite number of bubbles; you can think of them as foam. Each bubble is a universe, and began with its own “Big Bang.” Now where does a bubble come from? What existed before each bubble? The most reasonable answer is: the stuff that bubbles are made of. As each bubble grows and eventually pops, its remains are added to the substance that gives birth to new bubbles.
You might consider it the culmination of more than 2,000 years of study and recorded thought. Various branches of science have that: a new theory or discovery that not only blows away everything before it but makes them so unimportant they’re not even worth re-visiting. And usually, most of the tools, data, and supporting theories used to arrive at the new one have been around for some time. You have calculus in math, evolution in biology, plate tectonics in geology, straigth dope on the internet. 
Apollon writes:
> I see people say “we don’t know”, and others say “there was nothing”, yet they
> don’t bother to argue against the other. But they can’t both be right. Which one is
> it? We don’t know, or was there nothing?
“We don’t know” is all we can say with some reasonably good scientific support at the moment. I was going to say that we could say it for sure, but there’s nothing we can say for sure scientifically. We can’t even say that general relativity or quantum mechanics are true for sure. All we can say is that if we assume the Big Bang, general relativity, quantum mechanics, the Standard Model of particle physics, dark matter, dark energy, cosmic inflation, and probably several other things, we have a fairly consistent theory that fairly accurately explains the universe as we observe it.
“There was nothing” is not inconsistent with “We don’t know.” It’s just going beyond to make a further conjecture. “There was nothing” is one of several theories that makes such further conjectures. It’s the conjecture given as the Hartle-Hawking no-boundary condition in this list:
Older conjectures are that the universe’s expansion would slow down and stop eventually, producing a Big Freeze, or that the expansion would slow down and reverse, producing a Big Crunch, or that the universe would crunch and then expand again, for a Big Bounce. These conjectures were more popular before the discovery of dark energy. This is a list of those theories:
All the conjectures in these two lists are consistent with “We don’t know.” What they say is that we don’t know, but we can make some interesting conjectures. This is something that many non-scientists don’t understand which makes it hard for them to understand many announcements of scientific research (but which makes it easy for public relations people and journalists to fool them). It’s common that the announcements of interesting scientific research are actually written by public relations people at the company or university that the scientists who did the research work at. Their job is to make the research sound more established and more interesting than it actually is. The journalists who turn this into a news story then pump up the interest level even further. This is why you’ve got to be careful reading or listening to any news story about new scientific research. Research that hasn’t been peer-reviewed often gets announced long before publication. Interesting bits of observations are pumped up into being big breakthroughs. Pieces of speculation are treated as established fact.
So let’s try it this way:
To develop a theory, however speculative, of what might have been before the Big Bang, there should be at least a workable self-consistent mathematical theory of how it could have been.
What are some of the theories, however evidence-lacking they may be, that show a mathematically plausible model of the pre-Universe universe?
I think he meant geographically.
No, they are not silent about this. I am genuinely surprised that no one has mentioned the idea that prior to the Big Bang which was the beginning of our universe, there was a previous universe which had ended with a Big Crunch.
Well, no one mentioned except posts 11, 17 and 23.
Because there is no evidence and science is built on evidence. Compare Wittgenstein’s dictum: Whereof one cannot speak, thereof one must be silent. Of course, others can and so speak out of ignorance.
Of course, even scientists speculate, but label it as speculation, while admitting that it is unlikely that there will ever be evidence.
And each of them is simultaneously north and south of the other two.
No, once you define which point is the North Pole, there is nothing north of it. If you define the magnetic north as the North Pole, then go to the terrestrial North Pole (the one with the barber pole sticking out of it), then you have to go south to get to it. Of course the terrestrial North Pole, at the axis of Earth’s rotation, is the defined reference point being used by Hawking, because most people don’t know the magnetic NO is different.
My speculation is that this recent emphasis on the Big Crunch doesn’t come about because there is more evidence for it - there isn’t - but because it’s more psychologically comforting. A bouncing universe, bigger than smaller than bigger, is at least something that people can visualize. More so, at any rate, than a quantum fluctuation in vacuum energy. That has no real analog in everyday experience, which means it gets rejected regardless of whether it better fits today’s understanding.
Yep. It’s more comforting to think that the universe will ‘renew’, instead of pop like a soap bubble and cease to exist.
They’re answering subtly different questions. One can interpret the question as being one about the Universe itself, or one can interpret it as being a question about our current best models of the Universe. Properly speaking, to any question about the Universe itself, the correct answer is always “we don’t know”, because we can never know anything for certain about the actual reality of the Universe (see: brains in jars). But we can say things about our models of the Universe, and according to the best models we currently have, the concept of “before the Big Bang” is meaningless.
Now, there are also other models, less well-supported, in which such a concept is meaningful, and in some cases the model even provides an answer to the question. But then we have to say which model is correct, and we’re back to the first interpretation, about the actual real Universe.
Humans have been thinking about this kind of stuff for far longer than 2,000 years. Sure, it has only been recently that humans have gravitated toward a rigorous scientific methodology, but ancient attempts to solve the question tell us a lot about humanity.
I used to think that the general consensus was that time began with the Big Bang, but when I read The Fabric of the Cosmos, it was clear that at least Brian Greene thought that the consensus at that time was that it probably did not. (Things may have changed since then, or I may have misinterpreted.)
In any case, whether time began at the BB or existed before it, there’s really very little we can say about it. Most of what we can say about it is what we can NOT say about it.
The problem is, the Big Bang was a “singularity”. In math, a good example of a singularity is for a function y = f(x), where for some reason, at some x, y is not defined – and it’s not defined because of the very definition of the function: the answer doesn’t make sense at that point.
The simplest example is plotting 1/x. At x=0, the function is undefined. This is a singularity.
If the laws of physics say that a given condition causes a singularity, then what that means is there are some questions that we know we can’t answer based on the theory, because the theory predicts (demands) that it has no answer for that case. Not just that the answer is unknown, but that the question doesn’t make sense.
The BB is a singularity. The equations that lead us to it tell us that they can’t tell us much about what’s going on at the time – most of the functions “break down” just like 1/x at x=0.
For that reason, we also can’t say much about what came before it. The analogy between functions with a singularity and historical physics re singularities breaks down a bit there: with the function we can see what happens at x just below zero. But we can’t do that with physical observations and plug them in and extrapolate backwards from the singularity.
The math does tell us some stuff. For one thing, it tells us that information is not preserved. (At least, it used to … this may not be the case any more, since Hawkins lost his bet. Please help fight my ignorance!)
Greene points out that if the universe is infinite today (nobody knows, and the general best guess seems to change every few decades), then it also was at the time of the BB.
In any case, I think the answer is “First, there may not have been any such thing as time before the BB, since time is a part of the universe that was created by the BB. However, if time exists independently of the universe, then we just can’t say much about what happened before the BB.”
Of course, as mentioned above, there is a lot we can speculate about, including the quantum foam or the repeating Big Bang / Big Crunch.
BTW, the evidence against the Big Crunch is pretty solid, and the consensus against it is nearly universal (no pun intended). Stuff is flying apart, and there’s not enough density to pull it back together. For a Crunch to happen, the rules would have to change. Of course, the rules did seem change regarding one thing (early rapid inflation), so who’s to say it could never happen again?
The section I bolded makes me think of thisDeath by Puppets/Bad Astronomer crossover.
One tenant of rational thought is that some things you lack the evidence to make any conclusions about.
This is one of those things. Without evidence about “realms” outside the universe or before the big bang, no answers are forthcoming.
More importantly, you need to be ok with that. “I don’t know” is a valid and respectable answer. Moreover, it is a far more rational to say “I don’t know” instead of saying “I do know, because this dusty old book that cannot be verified says so. Also, I’m just going to ignore how 1000 leaders of other religious groups are all saying different things that confict with what I am saying, and how there is no way to test my claims.”
This is actually very much an ongoing debate, thanks to the recent ‘firewall’ controversy; it used to be that people believed that information was conserved, thanks to arguments having to do with the holographic principle (there is a description that is ‘dual’ to that of a black hole, which is just an ordinary (thermal) state in a quantum field theory, whose time evolution necessarily conserves information), leading to the proposal of ‘black hole complementarity’, which roughly says that both observers outside of the black hole, and infalling observers experience a consistent history, which are however incommensurable with one another.
The firewall argument, however, has eroded this consensus somewhat, because it appears to show that the above picture is inconsistent with some other things you would expect to hold for black hole physics, like an infalling observer not experiencing anything out of the ordinary when crossing a sufficiently large black hole’s horizon. Giving up on the unitarity of the evolution (that is, the conservation of information) is one way out of the dilemma, but one people are very reluctant to take, because it’s such a fundamental part of the quantum mechanical description of the world (personally, I have never understood how to make sense of a non-unitary theory; at the bottom, unitarity really says nothing but that all probabilities should add to one, that is, out of all possibilities, one necessarily occurs; if you repeal that, I don’t know what you’re left with).
There are a variety of theories, I have no idea how testable and falsifiable they are though.
I’ve heard it could be because two branes collided.
Our universe could exist at the bottom of a black hole in another universe.
The universe could have infinite cycles of expansion and contraction.
Universes could arise from bubbles in other Universes.
The OP should just read The Last Question by Asimov. It answers it all. 