"Gravity doughnut" may solve time travel problem
http://www.nature.com/news/2005/050711/full/050711-4.htmlOne of the major difficulties of travelling backwards in time has just been solved, according to an Israeli theoretical physicist. And the solution, he says, is doughnut-shaped...
...This is where Amos Ori from Technion, the Israel Institute of Technology in Haifa, comes in. He says that according to Einstein's theories, space can be twisted enough to create a local gravity field that looks like a doughnut of some arbitrary size. The gravitational field lines circle around the outside of this doughnut, so that space and time are both tightly curved back on themselves. Crucially, this does away with the need for any hypothetical exotic matter. [continued]