text: We observe four dimensions everyday, three spatial and time.\nTime is called a dimension because it makes mathematical sense to do so. \n\nBut...theories such as string theory predict that the space we live in has in fact many more dimensions (frequently 10, 11 or 26), but that the universe measured along these additional dimensions is subatomic in size. As a result, we perceive only the three spatial dimensions that have macroscopic size.\n\nThis is not so strange as it sounds, which I'll show with an example. Imagine you are in an airplane, flying over sea. Seen from a height, the sea looks flat, two-dimensional. But when the plane looses height we start to perceive the waves, that move in a third direction we could see before.\n\nThe universe could be the same. Four macroscopic dimensions and a few more, hidden ones. We can only perceive them for instance, by the small effects their existence might have on subatomic particles.\n\nThe Universe obviously can have a shape also if we consider the three macroscopic, spatial dimensions.  But before we take on the three-dimensional Universe first a two-dimensional example.\n\nImagine a two-dimensional plane. An ant walking on it can go in any direction, without finding a boundary. Secondly if it keeps walking in one direction, it will never come back on the same place. The plane is infinite, without bounds.\n\nNext the surface of a two-dimensional sphere. This time the walking ant again will not come to a boundary, but he will, after some time, come back to the some place. The sphere is without bounds, but finite.\n\nWe see that these two ant Universes are different, although a shortsighted ant, would never be able to distinguish the two.\n\nNext lets move to our Universe. We are short-sighted ants too. Our telescopes can not see far enough to distinguish if we are in the three-dimensional equivalent of the sphere of the plane.\n\nAnd it is even worse. As we are living in three dimensions more complicated space are possible. Imagine we are living in a cube, a special one with the following property. As soon as we leave the cube through one side, we enter it again on the side opposite where we left. This space is the 3-dimensional equivalent of a torus.\n\nYou see were we go: in three dimensions much more complicated space are possible.  Implausible? Maybe. Maybe not. At present we really have no way to tell. Just as the short-sighted ant.