Expanding universe needs a big bang?

[PeterDonis]

I've been reading a lot of articles that are seriously questioning the "big bang theory"...

You're going to need to give specific references if you want to take this kind of position. And if they're not textbooks or peer-reviewed papers, be prepared to be told that they're not valid sources for PF discussion. There are a lot of "articles" on the Internet that are not reliable.

 

[RandyD123]

You have that backwards. "If it happened everywhere how COULD there be a center" is the right question and of course that makes sense since there WAS no center.

You're right, I had it backwards. Thought about it after the post!

 

[phinds]

You're right, I had it backwards. Thought about it after the post!

So have you finally come to terms with the fact that there was no center?

 

[Ken G]

The model has no center. The model works well to fit the observations as simply as possible. That's all a scientist can say-- we should never say there either was or was not a center, this is a lesson we have learned quite a very many times by now.

 

[phinds]

The model has no center. The model works well to fit the observations as simply as possible. That's all a scientist can say-- we should never say there either was or was not a center, this is a lesson we have learned quite a very many times by now.

Good point. Thanks.

 

[RandyD123]

So have you finally come to terms with the fact that there was no center?

It's a hard concept to grasp. And then there is the "no edge"... meaning what are we expanding into! The universe is a very strange place indeed!

 

[Ken G]

The "no edge" element of the model is trying to cope with the "what are we expanding into" question, by essentially doing away with the question altogether. I would say an important feature of the Big Bang model is how it "does away" with pesky questions that we have no good answer for (like what is outside the universe, what came before, etc.). Having a model that does not need to address these questions because the model renders them meaningless is a useful aspect of the model, but of course it does not mean these questions are gone for good. It is always possible that some future model with resuscitate those questions by giving them testable answers, but for now, we just don't have any testable way to deal with those questions than simply dismiss them as meaningless, which is the approach taken in the current model.

 

[phinds]

Very good points @Ken G.

I tend to be absolutist in my statements about "center" and "edge", when I should be more clear that I am talking about our model as opposed to solidly known empirical facts.

 

[Ken G]

It's natural, we can always just assume that is what is meant. Sometimes it's useful to make the distinction though, because there are always room for surprises! Astronomy has rather a remarkable history of very big surprises, but then, I guess physics does too.

 

[Michaela SJ]

ed

Big bang is the hot and dense early state of the universe that one arrives at when one extrapolates expansion backwards in time.

Pardon my impertinence, but doesn't anything shorter than the length of Planck Time foreclose knowing what happened at the moment of the Big Bang.

 

[PeterDonis]

doesn't anything shorter than the length of Planck Time foreclose knowing what happened at the moment of the Big Bang.

The "moment of the Big Bang" in our best current cosmological model is not an "initial singularity". It's the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. In inflationary models, it's the state at the end of inflation, just after "reheating" has occurred.

 

[Drakkith]

ed
Pardon my impertinence, but doesn't anything shorter than the length of Planck Time foreclose knowing what happened at the moment of the Big Bang.

You're confusing the big bang as a single 'event' (creation of the known universe) with the big bang as a 'process' (rapid expansion from a hot, dense state). Bandersnatch is referring to the latter.