"The Universe In a Nutshell" by Stephen Hawking I'm reading the book "The Universe In a Nutshell" and I've become confused with a couple of parts.... "What do rotating Einstein universes have to do with time travel and time loops? The answer is that they are mathematically equivalent to other backgrounds that do admit time loops. These other backgrounds are unvierses that are expanding in two space directions. The universes are not expanding in the third space direction which, is periodic. That is to say, if you go to a certain distance in the this direction, youget back to where you started. However, each time you do a circuit of the third space direction, your speed in the first or second directions is increased." I don't quite understand what he's talking about (esp., his diagram doesn't quite make sense either). Thanks a bunch!