Just wondering.

Just wondering.
The answer is that it is not expanding into anything. Current scientific understanding has it that the universe is either closed in itself, or infinite ( we have insufficient data to decide which one ), but in either case does not have a boundary. As such there is no "outside" to the universe, it is not embedded into any higher dimensional space into which it could expand. The metric expansion we observe is an intrinsic expansion; I understand that this is a highly counterintuitive notion for which there is no real everyday analogue, but be assured that the relevant concepts are all mathematically rigorous and well defined. Bear in mind also that the universe is actually a 4dimensional construct, and as such is in fact static; all that really happens is that the geometry of that universe is slightly different at different points along the ( cosmological ) time axis  which is what we observe as metric expansion.
somebody else with nice rounded illustrations huh, KJW? Thanks for that explanation MH.
I'd say that infinity is outside of this universe and more universes exist that we cannot see yet. That is my opinion.
I think that the universe is expanding into a never ending complete vacuum. Although the universe is recognized as a vacuum, planets, stars, asteroids, and others make the universe an incomplete vacuum. So, the universe would be slowly dragged into the complete vacuum.
So you are ignoring Marcus' excellent explanation in post #2 then?
If you reread what Markus posted and think about what he said you will find that this is covered in that explanation.
The "complete never ending vacuum" that you mentioned would be included in the definition of "infinite" in his explanation. You could well have a finite amount of "stuff" (energy, matter....) existing in an infinite space. What we observe could be all that exists, unlikely but possible.
But I think we must clarify here that if the universe is infinite, this does not mean a finite universe expanding into infinite empty space, as sabodriver17 said. It means the infinite universe is full of particles, just like our observable part of the universe. The "complete never ending vacuum" would contain stuff and thus would incomplete by sabodriver17's definition.
According to our current understanding, the universe is either finite and full of galaxies, or infinite and full of galaxies. It does not expand into empty space, but rather the distances between the clusters of galaxies increases.
When we say the universe has no edge or boundary, what we mean is that there is no place where there are no more galaxies and just empty space beyond.
Curious About Astronomy: What is the universe expanding into?
Where is the centre of the universe?
New Proof Unknown "Structures" Tug at Our Universe"Dark flow" is no fluke, suggests a new study that strengthens the case for unknown, unseen "structures" lurking on the outskirts of creation.
In 2008 scientists reported the discovery of hundreds of galaxy clusters streaming in the same direction at more than 2.2 million miles (3.6 million kilometers) an hour.
This mysterious motion can't be explained by current models for distribution of mass in the universe. So the researchers made thecontroversial suggestion that the clusters are being tugged on by the gravity of matter outside the known universe.
[QUOTE] When we say the universe has no edge or boundary, what we mean is that there is no place where there are no more galaxies and just empty space beyond.
/QUOTE]
How then does this mesh with the concept of multiple dimensions required by string theory? As I understand it (in a highly simplified manner) universes exist as membranes in a ten or eleven dimensional "higher" universe. Wouldn't this imply that our three dimensional (4 including time) does expand into a higher dimensional space? Do these membranes grow?
On a related thought, don't three dimensional objects *require* a four dimensional space? (I'm talking only physical dimensions here) Consider: a zero dimensional object (a point) requires a one dimensional universe (a line) or it *is* the universe. Similarly, a one dimensional object requires a two dimensional universe, etc. This would seem to lead one to the conclusion that a three dimensional object *requires* a four physical dimension universe. Am I making a classic mistake here?
Interesting point (no pun intended). It would appear that multiple zerodimensional points would need to exist in a 2D or higher space in order to be distinct. But that appears to be an exception. Multiple 1D line segments can exist in 1D space. Multiple 2D shapes can exist in 2D space (look at the computer screen in front of you for an example). And very obviously, multiple 3D objects can exist in 3D space (look at the room around you).
However, when we talk about curved (4D) spacetime, you might think that that needs to be embedded in a higher order space. After al, we are familiar with the curved 2D surface of an orange being embedded in 3D space. But it turns out that for three dimesnions and above, curvature can be defined "intrinsically" and does not require a higher dimensional space. So, as far as we know, the universe is 4 dimensional.
When we talk of space in relation to our universe, we are using the same concepts as we use within our universe. We describe the universe with 3 dimensions for space (and 1 to represent time, as you say), so those 3 spatial dimensions are what I was talking about above. We do not think the 3 dimensions of space extend beyond the contents of the universe (this is based on things like the cosmological principle, the predictions of general relativity and the idea that the boundary conditions would leave a signature that we may be able to detect), so we do not think there is a place in those 3 spatial dimensions where the galaxies stop and there is empty space beyond. Higher dimensions are a different issue.
If the (3+1) dimensions of our universe were embedded in a higher dimension, there would still be no edge to our universe when viewed from within those (3+1) dimensions. A simple example is to use the topology of a 3sphere (a spherical 3 dimensional surface, rather than the 2spheres we are accustomed to seeing, which are only spherical 2 dimensional surfaces, such as a globe). If the universe were a 3sphere, then in any direction you look outwards into the universe, the straight line you think you are looking along is actually a very small section of a very large great circle that circumnavigates the universe. If it were possible to travel as far as possible in a straight line in the universe, you would end up back where you started.
These principles can apply whether the universe is embedded in a higher dimension or not.
If each moment is different than the next this would imply that each moment has boundaries relative to mass and velocity. This would mean traveling in a straight line and curving around and ending up where it started is relative to the moment. The reference frame is the fastest frame which in our case is the speed of light. A straight line traveling faster than the speed of light would start to curve. Traveling at the speed of light a straight line would be constant as it would stretch across each frame in every frame.
In an infinite universe, an infinite number of civilization obtain FTL travel, and not one but an infinite ammount of them. Likewise, wouldnt an infinite ammount of them decided to come take over earth.
This assumes 3 things. FTL is possible, we are not alone (which in an infinite universe is almost a mathmatical impossibility) and the universe is not infinite. If any one of these is wrong then we are still here. Im hedging that the universe is not infinite.
We don't really know, one way or the other, if our Universe is all there is and can only expand "into itself", or is expanding into a much larger existing three dimensional space, or is a threedimensional space warped into a fourth physical dimension. Or what about the Multiverse "theory"? Well, until it can be tested and disproved, it's not really a scientific theory, now is it. (Not a question)
Although I remember reading recently about the possibility of inferring the existence of other "universes" by their possible quantum effects on OUR Universe. Great stuff, cosmology. Where science meets philosophy and religion.
The neighbor's.
Read Paul Davies  'The goldilocks enigma'
The big bang was not an explosion IN space and time
It was an explosion OF space of time
I know this is an old thread with a very good answer at the top, but it seems like a decent enough place to ask this question.
In brane cosmology there a concept known as the "bulk", which is apparently some kind of weird hyperspace. Some models of brane cosmology have branes colliding and creating our universe. My question is this: In these models is the spacetime of our universe expanding inside that hyperspace? Or, if we could somehow observe from inside the bulk (as a thought experiment) would the expansion of the universe not be visible at all, as if it were expanding "inside itself".
My question posted today has a video link as shown here http://m.youtube.com/watch?v=MO_Q_f1WgQI&feature=kp this relates to a Brian Greene video which explains the 4 dimensions of spacetime rather well and could help you understand the expansion of the universe.
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