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A few things about the notion of folding space from a physics nut. To the best of my knowledge, the idea of space bending in any way comes from General Relativity, and the main (natural) mechanism for distorting space is gravity. In theory, the universe may fold in on itself and make a 4-dimensional sphere, however experiments don't reveal any curvature. It may be that we can't see far enough yet, but I personally believe there universe simply does not end. It may also be that the 'fabric' of space is finite, but will expand if matter reaches the 'boundary'. To those asking what's outside the sphere, the usual answer is that there is nothing. Not nothing as in empty space -- nothing as in no matter, no space, no time, no existence. You are refering to something that simply isn't there. The reason this is a popular answer is that spheres and donuts help visualize curved higher dimensional objects, but all other qualities (color, taste, being contained in even more dimensions) are not necessarily applicable to what they help you see. The donut helps you visualize curved space, but space itself is not actually a donut, whose 2d surface exists inside a 3d world. Think about this: the universe may be 3-dimensional, cubic, with no distortions (the 3d infinite object analogous to a plane -- exactly what most people think our 3d universe is). No one has much of a problem understanding conceptually that this is all there is to it, and there are no extra dimensions that contain such a universe. Well, if it were a plane, it would be 2 dimensional, infinite, and still may (conceptually) not be contained in more than 2-dimensions. When people talk about the universe being like a donut or sphere, they're talking about the SURFACE only, thus it is a curved 2d object. Such an object does not need 3 dimensions to exist -- just bend a 2d plane around until its inner geometry changes to that of a sphere (ex: angles of triangles no longer have to add to 180 degrees. Also, if you go in any direction long enough you return to where you started). Similarly the 3d cubic universe may be distorted so that our usual geometric view of it no longer holds, and it may wrap around and actually be finite in volume, however there does not need to be a 4th dimension for all this to happen. That being said, we have no more reason to ponder what's outside of the higher dimensional spherical universe than we do what's outside of our normal 3d cubic universe. The question arises because we're never trapped in the surface of a sphere. We always look at it from the outside, thus we falsely assume the outside is a necessary property of spheres and other curved objects.
[ Edited by think4yourself at
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