I am not a relativist or cosmologist, so this is very qualitative:
I imagine a pair of universes, where each has two spatial dimensions (plus time), embedded in a 3-D (plus time) space, and these two universes spatially intersect along a line. That line might even act as a "portal', from one universe to the other, for the flatlander residents...
Generalize that to a pair of universes where each has three spatial dimensions (plus time), embedded in a 4-D (or more, plus time) space, and these two universes spatially intersect, probably along a plane. Are they any theories, considered to be somewhat plausible, where 1) there are 4 or more spatial dimensions (plus time), 2) Our three spatial dimensions (plus time) universe is embedded within that, 3) there is at least one other universe (which also manifests internally to be three spatial dimensions, plus time) embedded in that higher dimensional space, and 4) that universe intersects ours? I am thinking probably not because, if there was one such other intersecting universe there would be an infinite number intersecting ours and so, things would appear quite different for us than they currently do.
