Does the model of how a ball falling through Flatland would appear to a Flatlander have any implications for theories about the Big Bang? It struck me that the Flatland example has some similarities (for me as a non-physicist) to the way the Big Bang is described. i.e not an explosion, but an expansion that is accelerating. My limited understanding is that the Flatlander sees a point appear from nowhere that becomes a line that lengthens as the ball falls through their 2-D world. I'm assuming that to the Flatlander the extension of the line would speed up as the ball moves steadily through the 2-D plane. From our 3-D viewpoint we can see the ball and also the way the circle it makes in Flatland grow in diameter. I wondered if Flatlanders, on the line that they see, would experience the sense that the distance between them was growing, no matter where they are on the line. If we scale this up dimensionally and imagine some sort of higher-dimension 'ball' that we as 3-D creatures cannot perceive directly, falling 'through' our universe, and the accelerating expansion of the universe from a single point being the result, along with the perception that everything seems to be moving away from everything else, no matter where you stand, are we seeing something like the Flatlanders experience, but in 3 dimensions? Or is all this just a coincidence?
 A: I've seen variations of this idea in more than one science-fiction story, but it doesn't make physical sense to me. We don't see objects as such, but light, which is an electromagnetic wave. If an object is visible then it must interact with the light, which means it has electric charge; but electromagnetism is confined to the lower-dimensional world, so what happens to that charge when the object leaves? Of course, a vision-like sense doesn't have to be based on electromagnetism, but I don't think you can solve the fundamental problem without making your "vision" some sort of nonlocal direct perception of (a lower-dimensional slice of) the world, instead of something mediated by a field. Once you do that, you're really talking about an abstract mathematical foliation of the higher-dimensional object, and not a physical passing-through process.
You definitely can take the 4D manifold of big bang cosmology, slice it into 3D pieces, and say that each slice represents a different "now". But there are many different ways of slicing it up, and none of them is any more physical than any other. (This is basically a restatement of the relativity of simultaneity.) There isn't any particular set of slices that represents what's really happening, or what anybody really sees.
