Derleth,
I don’t see the connection between curvature (intrinsic or extrinsic) and boundary.
J’s Friend
Your question of what happens when you reach the edge of the universe is like asking “What happens when you reach the edge of the surface of the earth? What would you see if you looked beyound the edge?” There is no edge. You cannot reach the boundary of the universe, because there is no boundary.
Yeah, all the time! But at least now I know why. Thank you.
Do astrophysicists abandon logical thinking when they don’t have a good explanation for something?
The idea that infinite space is expanding sounds contradictory to me. If, in the other case, space curves back on itself, who’s to say a galaxy viewed through the Hubble is not our own Milky Way seen through curved space? Are we expanding away from ourselves?
It was mentioned above that the Earth has no edges or boundaries. That’s true in the 2-dimensional model. Observable bodies in our universe are 3-dimensional with relative motion and boundaries. Why would the universe as a whole be any different?
Sorry if I sound combative, but I can’t accept pat answers for something so inexplicable. I’d rather hear someone say, “Well, noone really knows, but…”
DH
Of course there is. If I reach the surface of the earth and I look down I will see dirt if I look up I will see the moon. Sure if I look right or left it will just keep going, but space isn’t 2 dimensional. If the universe is expanding it has to be expanding into something. If it’s expanding in on it’s self then it’s not really expanding it’s kind of undulating. I guess that I’m just not getting it. I’m sorry if I seem stupid but I just can’t picture it in my mind.
The model of an expanding balloon is used as a model of an expanding 2D universe. The 2D inhabitants are only aware of two dimensions. They can slide north-south or east-west, but they know nothing of up or down; They will never reach the edge of their 2D universe. The corresponding model of our 3D universe would be an expanding hyper-sphere imbedded a 4D space. We have just reduced the number of dimensions by one so that we could visualize it. The only thing I would caution you about is that the higher imbedding dimension is a part of the model and is just there to make it easier to visualize; the higher dimension has no real existence. The universe is not expanding into anything we can detect. Something that we cannot even in principle detect does not exist as far as physics is concerned.
I apologise right now for not reading any of the other posts by anyone, and for not knowing anything about physics or any of those other sciences that deal with this sort of thing, but I’ll take a stab at this.
Logic would point to one answer, there is no center. Seeing as the universe is constantly expanding, the “center” would be constantly shifting from place to place. SO there is no set center. Plus since the universe is so large, it would most likely be near impossible to calculate exactly where the center is at any given time.
Again I apologise if anyone has already shared what I just shared now. I’m just too lazy to read the whole thread. 
sk8rixtx:
Right answer…wrong logic. Expanding things have centers. A balloon expanding has a center. The fact that the balloon is expanding outward has no effect on where the center of that balloon is.
Back to the ballon analogy for our Universe…
To us 3D people the balloon has a center. However, if you’re a 2D guy living on the surface (no up or down to him) there is no center. Either that or anyplace on the surface can be considered the center.
In our case we are a 4D hypersphere and our poor 3D minds simply can’t comprehend ‘up’ in a 4th dimension.
The center of the Universe is just right of Tuesday and back 20 minutes and slightly behind Friday. That’s probably what it’d sound like to us if a 4D creature gave us directions to the center of the Universe. Good luck getting there.
J’s Friend:
It helps understanding this if you can get your head around the concept of nothing. I mean really nothing. As DrMatrix pointed out if the Universe is indeed expanding ‘into’ ‘something’ it is meaningless. Outside the Universe is literally without definition. No time (no before and no after). No length. No up. No down. It is neither big or small (or it’s both). It is absolutely, 100% outside the realm of this Universe and therefore has no impact or meaning to anyone or anything in this Universe in any way.
Captain Kirk’s Transwarp Spaceship would be great but it seems that the Universe conspires to keep us away from the ‘edge’ of the Universe anyway. As far as we can tell the speed of light is an unbreakable speed limit (science fiction aside). Even if you travelled at 99.99999999999999% the speed of light you couldn’t catch the ‘edge’ of the Universe anyway (although at that speed the Universe would look mighty small to you).
Such hiding acts are nothing new to this Universe. The Heisenberg Uncertainty Principle is a well known and well tested feature of this space-time continuum. No matter how hard we try we can’t overcome that limitation on our ability to ‘know’ something. Catching the ‘edge’ of the Universe may be another such thing that we will never be able to get to even if such a thing did exist. The Universe’s very nature will conspire to hide it from us.
BTW: Star Trek: TNG had an episode where the Enterprise did travel to the edge of the Universe (an enigmatic traveller with them caused an insane burst of speed to get them there). Once at the edge their thoughts took tangible form since that’s where creation was actually happening (more Universe being created). You can go with that explanation if you like…it’s about as plausible as anything else someone can come up with.
Thanks for the mph’s, but sometime ago I asked whether our Local Group rotates, and several said it must because everything does, but it would be undetectable. If the Local Group rotates, then how would this affect our speed toward the Great Attractor?
This has kept me up all night on several occasions:
Given: The universe is expanding, so the distance between John’s house and Bob’s house is ever increasing.
Given: Our standard measurements used to be based on the size of the planet earth, so this would be UNmeasureable.
Given: Our new standard measurment is based on the wavelength of light.
Question: Can we now measure the increasing distance between Bob’s and John’s? Or does the lenngth of the wavelength of light change with our ever-expanding universe, and our units of measrue would still expand?
Everything (except for Higgs bosons, but forget I mentioned them) rotates, it is always detectible, since rotation requires acceleration and linear motion does not, and it would have absolutely no effect on the L. G.'s motion towards the Attractor.
likearock, the distace between Bob’s and John’s houses would only be increasing if they were in different galaxies far, far apart. The cosmic expansion causes space to expand, but it does not necessarily cause things in space to move apart from each other, if there’s other forces involved. For small scales, other forces (such as gravity or the electromagnetic forces that hold objects together) are almost always involved and far more significant than the spatial expansion.
Three good answers, all valid in different contexts:
(1) At right angles to everything else. This is not a sneaky Heinlein reference, although that is quite applicable. But the actual idea of expansion is conceptually difficult to express, and best done by analogy.
Mr. A. Square has taken his advanced astrophysics degree, and discovers that Flatland is actually one small area on a balloon which is inflating at a steady pace. Not being able to perceive the third dimension, he inquires, “Where is the center of the Universe balloon? All points on it are expanding away from each other. Some point, therefore, must be at the center.” But the center is not on the surface of the balloon, but in the third dimension, which he can only speculate about and cannot experience.
(2) Bosca had it right: Inwards.
(3) Up. Why d’you think steeples all point that way? 
There are elements of truth in all three. And aspects that prove any of them wrong.
I suspect this is one of those apparently meaningful questions with no true answer. Or an answer, or answers, that take one in unexpected directions.
How can infinite space expand?
Because if space was ‘closed’, the image of the Milky Way would still be too far away for us to see it.
Because the universe has 4 dimensions.
Building on likearock’s points:
Is the Milky Way expanding? It’s not a solid object, just a bunch of bits of matter near one another in space. Is this expansion detectable? Or is it drowned out by the much more dramatic motion going on (galaxy rotating, etc.)?
I’m located in Mount Pearl, NF.
I’m sorry. Everyone else seemed to be covering the OP’s topic REALLY well, and nobody had hit the obvious joke to this point. 