I am sorry if I am giving rushed responses Mechanus but I am trying to grab moments on this computer at very odd times (currently it is 3:30 am and I must be back on the roof in a few hours with no ability to stay and focus my responses as I am involved in a major reconstruction project under the threat of a hurricane.
Good luck.
You're correct that there is a sort of wall beyond which nothing can be seen ("surface of last scattering"). That wall is a part of the universe a few hundred thousand years after the Big Bang, when the universe first became transparent. If we could see beyond that wall, we would see the even earlier universe. At some point early enough, we no longer have a good idea what happens, because quantum gravity takes over. Looking even further (if it were possible) would correspond to looking at a time before the Big Bang. No one knows (yet?) whether there was anything before the Big Bang and what it was, although everyone seems to have an opinion.
However, what we see when we look far into space does not correspond to a situation that existed at any one time. The "wall" is strictly an artifact of how our perception is limited by the finite speed of light (if you lived in another galaxy, you would see the wall in a different place), and what actually exists at any one moment could well be an infinite universe. (Literally, actually infinite, going on forever, with an infinite amount of stars, planets, and so on.)
You mention a center of the "blast", but it's generally believed that there is no center -- the Big Bang happened everywhere, or nowhere, depending on how you look at it. The expanding spherical "wall" is centered on Earth (or on whoever is doing the observing), not because this is a special point, but because that's where we're looking from, and only the light from a sphere of finite radius (the visible universe, or observable universe) has yet been able to reach us. If there is a "cosmological constant" that causes the universe to accelerate its expansion, then this sphere will (AIUI) reach a finite maximum value at some point in the future (probably only in several billion years, if I recall correctly) and then start to contract. If there is no dark energy causing the universe to accelerate, or if there is but it goes to zero, then the observable universe will grow to encompass the entire universe (over an infinite amount of time).
The math of that is still highly speculative and I do not think it is helpful to act supercilious about it, hence it is not behaving like a "crackpot" to acknowledge we know a lot less than we speculate about.
I did not mean to give off the impression that everything is already known about cosmology. There are a lot of big open questions (how did the universe begin, is it infinite or not, will it expand forever, is there one or more, what's up with the cosmological constant, and so on). On the other hand, there is a lot that is known (that there was a Big Bang, that general relativity and quantum field theory are approximately right, and so on), and cosmologists have good ideas on what sort of answers may and may not be plausible for the big unknown questions. I don't think it's unfair to consider those who reject these mainstream ideas without understanding them "crackpots". This probably does not include you, though, sorry about that (I was a bit annoyed with how the forums here seem to be overrun by a wide variety of loonies (by which I again do not mean you!)); I wasn't sure whether that was what you were saying, which is why I asked. "Sorce theory" definitely falls under that definition of crackpot.
I was speculating about how two seemingly unrelated areas of theoretical physics may overlap logically and BTW there is very little verified and quantifiable evidence to support any of these theoretical models as of yet so please do not behave so parochial so as to decry anyone that doesn't agree with you as a "crackpot".
I never used the word crackpot in connection to this overlap between string theory and multiverses -- I just don't understand what you mean. Is it anything like
this, for example?
I don't think there's an area of theoretical physics that deals with multiverses in general, although there are a few areas of physics that involve multiverses (many-worlds QM, eternal chaotic inflation, etc.)
"In short, science at its finest: nobody knows what the heck is going on! But we'll sort it out soon, and then we'll sadly have to move on to the next question.
(I wrote the last sentence because I know from bitter experience that otherwise some crackpot will fasten on my previous remark and say "Baez admits that in science nobody knows what's going on! Therefore my insane theory could be right: Mars is a neutrino! Nyeh nyeh!")" -- John Baez
I have also found that what isn't expressible is also not so clearly understood.
This is often true, but there's no guarantee the expression will be simple or straightforward. Physical theories generally aren't simple or commonsensical or intuitive, and any presentation that makes them seem that way is leaving out most of the subtleties. The only thing one can do is to explain very carefully how everything works, what mathematical concepts are used and how they correspond to our intuition, and so on. I see this happen much more in places like internet newsgroups and FAQs than in news articles or many popular science works. Many explanations seem freely associating and sensationalistic to me, only vaguely mapping to the actual physics, leaving the reader to fill in most of the details, often wrongly.
If you can explain something in physics or especially mathematics to your grandmother, then you have probably not understood it.
LongeCity
