first i would like to ask a question .. imagine there are 2 dimensional creatures that are able to live and interact . they can exist in the second dimension with no problems . can the surface of a sphere precieved as a valid 2 dimentional space that these creatures can exist in ?( if yes then continue reading , if no then i am making an invalid point here). the problem with that space is the fact that it's bent in the third dimension . if this 2 dimensional creature would go in any direction in a straight path , he will return to his main position over and over again . now , for this to be applicable to the 3 dimensional space , it has to be bent in the 4th dimension . if the surface of a sphere is the 2 dimensional world existing within the 3rd dimension then the infinite number of Surfaces of the infinite number of 3 dimensional spheres should form the 3 dimensional surface of the 4 dimensional sphere . so the 3rd dimensional space that can have such properties is the surface of the 4 dimensional sphere ... then if i would be living in the bent 3 dimensional space and i move towards any direction after reaching the edge of the universe (i wouldn't even notice that an edge exists) i would return to my starting point all this is caused by the space is being bent in 4 dimensional space . now how can we actually figure that space isn't in someway bent in 4 dimensional space ?