I'm not a professional cosmologist, but - as I understand it - we don't care if there is any material "farther" from the imaginary inflating shell, or closer to the "center" (whatever those words mean - we must understand that time and space were created in the Big Bang[1].) Bake a loaf of bread with raisins. As the dough rises, all raisins move away from each other; but any two raisins don't care what other raisins are doing - they aren't affected by that. Similarly, dots on a balloon don't care if there are larger balloons outside or smaller balloons inside.
How would that necessarily be so? If light emitting objects existed further than 13 billion light years away yet have existed longer than 13 b. years then the light could be reaching us now. Say; an object 20 b. light years away that has existed for 30 b. years. No?
Yes, with one little catch - the age of Universe is about 13 billion years. So if there is an object 20 billion light years away it can exist only for 13 billion years (even if we assume that it got there instantly[2]) and therefore we have to wait another 7 billion years until the light from it reaches us.
In other words, there is no object in this Universe that is older than the Universe itself, and as result we can't see past the point of birth of the Universe.
Now heat the barrel until bubbles of steam are released. Now you have the boundary, and as long as those bubbles last long enough you just created a bunch of Universes for little 2D civilizations of water spiders to sprout, eventually. And if you rework the whole model one dimension higher you can see how our 3D Universe could "condensate" out of space with higher dimensions.
But take a large sheet of plywood and drop it onto the surface, flat. It will make contact at every point of its surface at the same time - instantly. The water spider's physics would be shattered - he just observed an instantaneous action without any propagation! But that is possible only because the interference came from another dimension (from above the water.) One theory of BB suggests that BB could be a spark, a collision point between objects of higher dimensions.
Yes, I get the balloon analogy but the question isn't whether the raisins care about what's going on in the center. The question is; there is a center isn't there?
Yes, with one little catch - the age of Universe is about 13 billion years. So if there is an object 20 billion light years away it can exist only for 13 billion years ...
Assuming it is a part of the universe created by the BB. Which I didn't.
In other words, there is no object in this Universe that is older than the Universe itself, and as result we can't see past the point of birth of the Universe.
Unless the light of something much older than this universe was passing through this universe.