This question already has an answer here: Symmetrical twin paradox in a closed universe 3 answers This is a question from the book "The Special Theory of Relativity" by DENNIS MORRIS. This question is from the chapter "The Nature of Straight Lines and the Twin Paradox". Page no:181 Suppose the spacetime of the universe was like the surface of a higher dimensional sphere (Riemannian) in that one could travel infinitely far within it yet it is of finite extent. (There are cosmologies that accept this view). now suppose the two moving observers pass each other without any acceleration as they travel around this sphere and suppose they meet again billions of years later during which time neither of them has changed velocity. They have both travelled on straight lines through space-time. Who will be the younger? Does this mean that the spherical view of cosmology must be incorrect? Login To add answer/comment