One of the major difficulties of travelling backwards in time has just been solved, according to Amos Ori from Technion, the Israel Institute of Technology.

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.

Ori says the mathematics reveal that every period of time between when the doughnut was created and the present moment would be somewhere in the vacuum inside the doughnut. All you need to do is work out how to get there.