>>10991392To try to think about how the universe is 4D, its better think about a 4D Lorentzian space than to think about a 4D Euclidean space like the 4D cube you've drawn there. In the Lorentzian topology, the 4D shape is a hypercone, and it is actually quite easy to visualize how the universe fits in with it. With the 4D Euclidean cube in OP pic, it is not easy at all to tell how the universe fits in there... because in fact it does not, because in fact the real 4D universe has Lorentzian topology rather than Euclidean.
We know distance in space is real, and the universe would be Euclidean is distance through time was real too. However, if distance through space is real, then distance through time is imaginary, and then the 4th dimension is different than the other three. Likewise, if you take the convention that distance through space is imaginary, then distance through time is real. However you cook it, distance through time always has a complex phase with respect to distance through space, and that is why the hypercone is the correct 4D with which to visualize the universe.
>A four-dimensional right spherical hypercone can be thought of as a sphere which expands with time 
