The balloon analogy is just an analogy. It is not supposed to represent expanding 3D space. It represents what expanding 2D space could look like. The balloon has no thickness or you could imagine that the objects within the 2D universe are as thick as the balloon. For observers confined to the balloon, there is no way to observe anything not on the surface of the balloon. The embedding space is not real to the balloon universe.
It might help to understand that space-time curvature is really a mathematical versus a physical concept. It refers to a curvature in the intrinsic geometry of space-time not an actual extrinsic curvature. Three D space can’t curve into some fourth spatial dimension because there is no fourth spatial dimension.
For instance in the vicinity of massive gravitating body the circumference of a circle doesn’t equal 2pir so something has changed but it has to do with warpage of the internal geometrical distance scales not some bending of space itself.
Having said that I still don’t know of any better way (however flawed) to visualize an expanding universe then the old balloon analogy.
Thanks, it did.
trader…shots
“Given that the above is correct ( just for arguements sake) would that mean there there IS an edge to the universe and if so - what do you surpose would be on the other side ?”
I don’t see arguing shape, size, center, etc. is helpful in answer to the OP. Although, I love the subject!
Q: What’s out there? If this universe is expanding (bang), then a different universe (probably several) is “crunching”. Don’t suppose I need to explain the Oscillating theory.
Yeah, there’s something beyond our universe, or what WE identify as our universe. Some are expanding, some are collapsing…the real trip would be the possibility of going from one to another.
IMHO…Peace
Quite; the skin of the balloon is Flatland.
I suppose it would be reasonable to ask if there is any higher-dimensional embedding space in which our 3+1 dimensional universe floats…
And to further confuse things you might want to think about this brain eater: If the universe is open and infinite then it has always been open and infinite.
If you like brain pain then dwell on an infinite universe existing from the instant the Big Bang occurred.
Reasonable to ask, perhaps, but not reasonable to answer. It’s not (necessarily) that the embedding space doesn’t exist; it’s that regardless of whether it exists or not, we can’t detect it. If it makes you feel more comfortable about it, sure, go ahead and imagine an embedding space. But when you’re doing the math, it’s far simpler to deal with extrinsic curvature (which can be measured by us folks in the Universe), and just ignore the possibility of an embedding space. Besides, Occam’s Razor comes in: If you can describe a self-sufficient curved universe, why go to the trouble of describing a curved universe with stuff outside it?
So, if I go far enough in the Universe, I will eventually reach a point where I am coming back?
If you start around the surface of a balloon, you will eventually come back to the point you started. The analogy works on the universe, too.
Assuming that it’s closed, which it probably isn’t.
Head…hurts…must go to next topic…