The Universe is infinite: it has no bounds, or limits.<p>For instance, you can go on a straight line forever.<p>It "expands", but it does not "swell", because it does not mean anything for a boundless space to be "swelling".<p>The "expansion" phenomenon, known as "metric expansion of space" [1], is not "swelling" at all. Only the spatial scale of the Universe is expanding.<p>Furthermore, this process is isotropic, which means wherever you are observing from, it will always seem like you are at the center of the expansion process.<p>[1] <a href="http://en.wikipedia.org/wiki/Metric_expansion_of_space" rel="nofollow">http://en.wikipedia.org/wiki/Metric_expansion_of_space</a><p>EDIT: fixed typos (damn keyboard)
if you mean "what does the universe expand into?" then the answer, as far as we know, is that "it doesn't work like that".<p>another way of saying the same thing is that the maths used in the physical models doesn't "embed" the universe in anything. there's no need for an external reference. you can do everything internally, consistently. it's quite neat, actually.<p>that doesn't mean that there "really is" nothing. just that nothing extra is needed for the theory, and since nothing extra can be observed, it's simpler to not have anything.<p>in other words - you can mathematically describe a universe that expands, but doesn't need anything to expand into. since that fits observations (within reason) and is simpler than a model that needs something extra "outside" that also needs explaining (and how would you explain that?!), it's preferred.
From what I understand two terms you use would be inaccurate. First of all it's not an area, as it has no physical dimensions. Second of all it could not be called 'eternity' as it is composed of nothing and therefore no change to it is occurring, and change is the fundamental principle behind time.<p>Everything that exists, exists within the universe, there is nothing 'outside', there is no 'outside'. At least under the classical understanding, or theory, of existence. Some multiverse models posit that there may be other universes that we may one day expand into. Others yet posit that these other 'bubbles' might have differing laws of physics to us, and could destroy us on contact. Fun.
It's not called anything because it doesn't really exist, it is outside the horizon of events. Think of it same way as about volume which is inside a black hole. It doesn't exist... until you get there. Then the world outside the hole will become nonexistent to you, exactly same way as the area 'outside the universe' is to us now. Because the black hole will become your universe. In a way, we are sitting in a giant black hole.
The simple answer is: the universe.<p>Just today, Fraser Cain posted a video to answer this question.<p>Have a look :
<a href="http://youtu.be/Kj0TwTonG_8" rel="nofollow">http://youtu.be/Kj0TwTonG_8</a><p>Hope it helps!