How big is the Universe?

Like all analogies, it can get conceptually confusing.Think of the skin, and the entire balloon, as the universe at this moment in time. And, think of the balloon expanding as time passing from moment to moment; the increase of the balloon in size is time progressing forward.If you can piture that, now imagine placing dots all over the balloon. These dots represent galaxies in our universe. Now, as you increase the size of the balloon - (as it increases remember that's time progressing forward) - you'll notice that the dots, while not moving from where you drew them, are getting further apart from each other. The space between each dot is expanding due to the balloon increasing in size.Likewise, the space between the galaxies is increasing due to the accelerated expansion of the universe.That's why there's no speed of light restriction, because nothing is really moving at any speed. It's just the space between it that's increasing. Edited by onifre, : No reason given.

Hi Buz, There is no outside of spacetime either, I didn't mean to lead you to that opinion.What is meant by spacetime being finite is that it had a point of origin, the BB 13.7 bya. However, it didn't come from nothing. What existed before that doesn't operated under the same space and time dimensions that we experience, so it makes no sense to say when that 'started', the universe just is.There is no outside of it, it is exitence.And yes, spacetime is expanding, but it can equally be said that the universe is expanding because spacetime represents the universe ever since 13.7 bya.- Oni

Hi Buz, Fair enough, just know that that wasn't what I was trying to convey. No, just existed; no space or time. Similar to Hawking's No-Boundary universe? - Me thinks the gentleman in the wheelchair worked out the math before you, Buz. Why go the extra step? Its suffice to say the universe is; there is no need to add to the equation your particular mythical entity - however, if it makes you personally feel better, then postulate away ... just don't expect people to take you on faith. If this is in reference to Hawking's no-boundary universe, its size (as we define it) that is finite, not the universe - We stop defining size at Plank scale. Huh? The reasons are known. Who said the reasons were unknown? You are misunderstanding and confusing certain terms.Spacetime is finite in size, Plank scale, the universe has always existed - In other words, existence has always existed.- Oni

Hi Buz,I'll try to explain a bit further, as I kinda understand your position a bit better. What is meant by "spacetime" is a description of the geometry of the universe, ie. Minkowski spacetime. That is finite in size down to Plank scale.This had an origin, the Big Bang. Sort of, but necessarily with different space and time dimensions; remember, as dimensions, space and time are experienced by things with mass, to speak of it any different is losing the meaning of what space and time dimension are.There is no "time" as in beginning and end in our universe (or rather, no beginning or end to existence it has always been, there has always been something instead of nothing); there is no back in time or forward in time; these concepts are only relevant to thing which experience it. So to say "before the universe began" is nonsensical because time is a non-factor to existence itself. Actually, they are both different yet both the same - this may get confusing, and it is also where I get confused a bit as well. So if I screw this up I'd hope it gets caught by someone with more knowledge than me.The universe from this point forward will be regarded as "existence" (ie. something instead of nothing) - spacetime will describe the geometry (Minkowski) of the observable universe.In this sense, existence has always existed, but spacetime geometry had its origin at the BB - which is the point where we can describe the "space" of it because it expanded past Plank scale. Smaller than this scale, and we lose the ability to describe "space". I think the confusion comes in when the conversations are trying to describe spacetime as infinte, when it obviously is not. However, it can expand to infinium, and thus we can have spacetime (geometry) that has a finite origin but an infinite "future" so to speak.You have to be careful how you word things. If you say universe, as we experience it (4D spacetime) then yes, it is finite in origin. But, if you mean universe as in existence (ie. something instead of nothing) then that has always exited - ie. existence has always existed.This is where conversations overlap between physics and philosophy, and many (including myself) get confused. To postulate a "time" before existence is nonsensical, but fun for philosophical musing. To postulate a "time" before spacetime, is sensical and is what theoreical physicist are pondering and coming up with hypothesis for (String, M-Theory, multi-verse, etc.). It can get confusing when you overlap the two fields of study.The BB did not create existence, but, it is a moment in the history of the existence of the universe - the moment when spacetime expanded.I hope this cleared it up a bit more for you, and I hope I explained it right.- Oni

Thanks cavediver,Just when I think I have some of it figured out, I don't. So what would you describe it as? I meant that it was finite in size, would that be a correct way to say it? Ah, ok.Is this what you think it is, or do you think (know) that it wraps back up on itself?For the most part, was my explanation to Buz sorta on point? I hope I don't come off as a know it all, I just like posting my perspective because its the only way you (or SonGoku) can correct me.- Oni