Gan_HOPE326 said:
But I'm not sure this question really makes sense...
...
But, they're all internal laws to OUR universe, right? So, why should our universe need "space" to expand? It's just that it can "contain more matter" second after second.
Plus, expansion is a temporal concept: but if we want to take a look to our universe from outside, it's got to be four-dimensional (or even worse...). Then, its shape is already determined in all of the four dimensions: the space for the future, bigger versions of our universe is already booked!
Thanks Gan_HOPE326, for taking the time to try to answer this 'impossible' question.
I know this is a 'little bit' outside the mainstream cosmology, and extremely difficult to 'talk' about. Ned Wright gives this explanation in his FAQ -
http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN":
"
This question is based on the ever popular misconception that the Universe is some curved object embedded in a higher dimensional space, and that the Universe is expanding into this space. This misconception is probably fostered by the balloon analogy which shows a 2-D spherical model of the Universe expanding in a 3-D space. While it is possible to think of the Universe this way, it is not necessary, and there is nothing whatsoever that we have measured or can measure that will show us anything about the larger space. Everything that we measure is within the Universe, and we see no edge or boundary or center of expansion. Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about."
This is perfectly clear to me. And the odds to get the Nobel Prize in studying "the thing outside" our universe, is not outstanding. The Holy Grail of this question is this line:
"
Thus the Universe is not expanding into anything that we can see, and this is not a profitable thing to think about."
This is also perfectly clear to me. Why should a professional scientist spend valuable time on this 'impossible' question? There are thousands and thousands other questions with much better prognosis for a real solution... Reasonably - this is 'stupidity' and a waste of time (
for a pro).
But for me, as a layman, it's extremely interesting and fun to speculate about. And it doesn't cost me much (
in status or money).
I also have come to the conclusion that "the thing outside" probably must have extra dimensions, additional to our four-dimensional spacetime. But I'm not sure I can follow your reasoning all the way:
"
... the space for the future, bigger versions of our universe is already booked!"
Take a look of http://upload.wikimedia.org/wikipedia/commons/3/32/Embedded_LambdaCDM_geometry.png" (Lambda-Cold Dark Matter) cosmological model, showing one dimension of space and one of time (
the red line is the path of a light beam emitted by the quasar about 13 billion years ago and reaching the Earth in the present day).
How can we state that geometrical status of our universe in 13 billion years from now "
is already booked"!?
I could be wrong? But doesn't this mean that our universe is
perfectly deterministic?? This is
NOT what the QM-guys (
quantum mechanics) are telling us?? We can make very good mathematical predictions, but noting is absolutely written in stone - about the future?
So, how can we state anything 100% sure about our universe in 13 billion years from 'now', and how can the 'future space' already be "booked"??
(
An easy way to get rid of this problem is to say - Yeah, yeah Dude! And what do we know of the determinism in "the thing outside"!? Absolutely nothing, nada, zero, zip! 
)
Another thing that often pops up in this kind of discussions is "extra dimensions". But I'm not sure this satisfies me. Take one thousand extra dimensions, and you still have the problem of a physical reality that seems (
in some way) impossible...
Dmitry67 (
thanks!) talks about "
the Cosmology point of view, which is really a ‘God’s eyes view’, or ‘Bird’s view’" (and I like that very much!). Now with this view -
visualize our observable universe - 14 billion parsecs (
46.5 billion light-years) at least. And according to Alan Guth (
founder of the theory of cosmic inflation), the entire Universe could be at least 1023 to 1026 times as large as the observable universe.
Imagine the enormous amount of matter/energy in our giant universe. And
recall that only 4% of the universe is ordinary matter/energy that we can see -
96% we cannot see (
Dark Matter & Dark Energy).
How on Earth can this extremely 'heavy thing', that is our universe, just 'float around' in some weird nothingness? That furthermore doesn't exist!? And at the same time provides more 'room' for our extremely fast 'expanding giant'??
This is an absolutely mind-blowing thought - no matter how many dimensions you add to this scenario -
you always run into the 'irrational wall'. To me it seems as an impossible construction: A never-ending series of a "Russian Nested Doll"-reality. If you find the answer for "one doll", then instantly a new question needs to be answered -
Okay, AND what kind of "doll" is this one 'floating' around in??
My guess is that our brains are not developed enough (
yet 
) to comprehend this 'recursive reality loop'. Or... the universe and our existence is a fundamentally impossible construction that really cannot exist - in the way we percept the world...
(
And I still claim; I'm not crazy... yet... 
)
(
Dmitry67, thanks! I'll be back...)