why do we consider just 1 unique big bang event?

[Oblivious]

Hi, It could be a silly question but it is related to the M theory and any previous theory for explaining the universe by which we consider just 1 single starting point for the 'universe'. But and assuming that the previous sentences are correct, why we do not consider that starting point as a local one? then what would happen if we consider N starting points?, as first sight that may allow considering a broader set of dimensions, can anybody Imagine the impacts? which would be the possible models for such speculation?
I'd love reading some one from you guys.

[Surlethe]

The only evidence we have comes from the observable universe, and that evidence suggests the entire observable universe was a single point $13.7\times 10^9$ yrs ago. How do you think it could be more than one point? Space is connected, after all; if there were multiple singularities you would, I think, be able to disconnect the physical universe at some time in the past.

[Darth Wong]

Simple answer: that hypothesis is not necessary. It does not solve any problem.

There are a lot of speculative ideas, from multiple universes to God to The Force, which fall under this category.

[Kuroji]

We aren't able to get enough information from the starting point of this universe to speculate on the existence of any other universes that we might be a part of, that we might have budded off from, or that might have budded off of ours.

If that sort of information became available, it would be nothing short of revolutionary, but I don't think anything is going to make that available in our lifetimes unless we suddenly become able to access other universes. And even at that, if there are other universes in existence, the local laws of physics may very well be anathema to us. Who's to say they even have elementary particles, let alone that they are the same as ours? Who's to say that gravity, the speed of light, the laws of thermodynamics, the flow of time, etc, work the same as they do in our universe? If there are multiple universes it's pretty unlikely that most would share the same configuration that allows for life as we know it.

[Kuroneko]

Hi, It could be a silly question but it is related to the M theory and any previous theory for explaining the universe by which we consider just 1 single starting point for the 'universe'.

We don't; the Big Bang singularity was three-dimensional. If you're asking why it looks the same everywhere, it's really just an assumption of homogeneity, which is extremely well-supported by observational evidence, such as WMAP. One could imagine a chaotic, heterogeneous gravitational collapse, where a very non-uniform matter distribution collapses at different rates, and then run the whole thing in reverse to get a 'big bang' with an extremely complicated singularity instead.

But and assuming that the previous sentences are correct, why we do not consider that starting point as a local one?

Again, we don't. The big bang singularity is global--it's everywhere, not at some particular point.

Unless you mean other universes, in which case that has already been addressed.

[Steel]

While this isn't what the OP means, there actually probably was more than one 'Big Bang'.

With the theory of inflation you have the standard hot big bang preceeded by the period of inflation. So in fact you have an expansion from the singularity and then reheating and the standard hot big bang. Two phases of 'bang'.

[Oskuro]

There's something I've been wondering about recently. Since we can tell the Universe is expanding thanks to the redshift of distant stars, has it been calculated where, aproximately, the origin point (the center of the universe) is? I mean, if the expansion of space from t=0 is uniform, it should be noticeable (I think).

[Junghalli]

There's something I've been wondering about recently. Since we can tell the Universe is expanding thanks to the redshift of distant stars, has it been calculated where, aproximately, the origin point (the center of the universe) is? I mean, if the expansion of space from t=0 is uniform, it should be noticeable (I think).

As I understand it there is no such thing as a center or edge to the expanding universe in 3d space. Space is expanding evenly away from all points simultaneously.

[Singular Intellect]

Hi, It could be a silly question but it is related to the M theory and any previous theory for explaining the universe by which we consider just 1 single starting point for the 'universe'. But and assuming that the previous sentences are correct, why we do not consider that starting point as a local one? then what would happen if we consider N starting points?, as first sight that may allow considering a broader set of dimensions, can anybody Imagine the impacts? which would be the possible models for such speculation?
I'd love reading some one from you guys.

You're going about the process backwards. You gather and analyse existing evidence, and then formulate conclusions based upon that.

What you appear to be doing is creating/appealing to conjecture and speculation, and then trying to justify it with further conjecture and speculation. Even if you were actually seeking evidence to substantiate your ideas, you're still going the wrong way in attempting to determine the reality of the universe.

[ThomasP]

Regarding the Big Bang and singularity, I read this the other day and was curious about further discussion. The relevant part, images snipped:

Well, quite clearly, a Universe with exponential expansion expands the fastest over time, and one with matter expands faster than one with radiation. No big deal. But I want to go backwards, and take a look at what happens when we extrapolate back to a time where the size of the Universe should shrink to zero! After all, that's what a singularity is defined to be, where all of the matter and energy in the Universe is concentrated in a single point. Let's calculate it and see what we get.

What's this?! A Universe with matter or radiation totally has a singularity at time t=0, but -- and this is very, very important -- an inflating Universe does not! In fact, we can take the inflating, exponentially expanding Universe back arbitrarily far, and what do we find?

It never reaches a size of zero! If you want an inflating Universe to have a singularity, you need to go back an infinite amount of time! Physically, of course, we can't do that. The only information we have about inflation is from whatever comes at the very end of it. Everything else is wiped away from our field of view by the exponential expansion!

So what does this all mean? It means the idea that our Universe started from a singularity was a very good one back when we thought that the only important things in our Universe were matter and radiation, but now that we know about inflation, there is no reason to believe that our Universe ever had a singularity in the past.

And this is different from what you'll read almost everywhere -- on the internet, in textbooks, even at many colleges and Universities -- but it's right. Now that we know about inflation, it's time to admit that we can't with any sort of certainty speak about what came before it. That means there is no reason to believe that our Universe came from a singularity, and this outdated idea should have died as soon as inflation was accepted.

And isn't that a surprise for most of us! So my answer -- to the best of our current knowledge about the Universe -- is no, it didn't. What do you think about that?

It sounds like he's saying there's still some threshold of "meaninglessness" (for lack of better wording on my part), even if it's not a black hole kind of singularity. What that implies, I have no idea, but I'd be interested in any elaboration.

[Kuroneko]

A universe dominated by a cosmological constant is approximately de Sitter, and de Sitter spacetime has a scale factor proportional to exp(Ht), where H is a constant Hubble parameter. That obviously expands exponentially without a past singularity, so he is completely right in that an "inflating, exponetially expanding Universe" has no singularity.

What's this?! A Universe with matter or radiation totally has a singularity at time t=0, but -- and this is very, very important -- an inflating Universe does not!

That's wrong, or more precisely, it does not follow at all. Cosmic inflation is theoretically driven by a certain kind of field, and the claim that the universe was in the above form is equivalent to this inflaton field being stuck in some potential minimum for an infinite amount of time beforehand--until one day it wasn't. That's incredible, and we'd need some very good reason to believe that was the case.

And this is different from what you'll read almost everywhere -- on the internet, in textbooks, even at many colleges and Universities -- but it's right.

Eternal inflation is a very broad class of inflationary models, and most of them are much more complicated than assuming that the universe was approximately de Sitter in the past. That isn't in any way uncommon knowledge in textboooks that deal with the subject.