My question may be wholly ignorant, substituting metaphor for physics, and if so, I apologize in advance.
There’s a flat pool of water. A drop falls into it, and ripples begin to radiate outward from the drop. Little bugs living on the surface can’t travel faster than those ripples; the expanding ripples comprise their entire universe.
If we submit that the ripples comprise space, does that function as a two-dimensional metaphor for our universe?
Is it coherent with the metaphor to imagine that other drops would fall into the pool elsewhere and create their own expanding ripples?
Is it possible that eventually the ripples will intersect?
I guess it is not a good analogy? Because the unstated cosmological assumption here is of a homogeneous, isotropic universe
so no ripples; there is just a scale factor
measuring the expansion (so doubling it stretches distances by a factor of 2, for instance).
I guess by “ripple” you in fact mean the entire universe… if you had, let’s say, two disconnected pieces (“ripples”), off the top of my head they could not at some point merge together (or, in the other direction, the universe expand in such a way that it split in two pieces).
It is possible that two planets, widely separated in the Universe, might have two different observable universes, that start off separate but which eventually, after some amount of time, overlap. In fact, this inevitably happens all the time. But each of those “boundaries” would have no significance whatsoever for anyone but a resident of the planet at its center. In particular, if you were at the point where those two spheres were intersecting (and everyone is at such a point, for some pair of spheres), you wouldn’t notice anything at all about it.