A professor at the University of British Columbia has claimed that time travel is mathematically possible, though we’re unlikely to take advantage of said possibility in the foreseeable future.
According to Phys.org, Ben Tippett’s mathematical model appears in a study he recently published on the “feasibility of time travel.” It’s all a bit complicated, so I’d encourage you to head over there for a more detailed explanation, but to summarize:
According to Einstein’s theory of general relativity, Tippett says, it’s incorrect to think of time as a dimension separate from the other three spatial dimensions. Instead, all four dimensions (or directions) are connected, making up the space-time continuum.
When space-time is warped (as with massive objects in space, like black holes), the time direction also “shows curvature” just like the others. The closer you get to those massive objects, the slower time flows.
Using this concept, Tippett created a mathematical model in which a “time machine” – a kind of “bubble” he’s dubbed the Traversable Acausal Retrograde Domain in Space-time (or, uh, TARDIS) – would travel around a “large circular path,” occasionally traveling faster than light, bending the time dimension “into a circle.” This would ultimately allow for time travel backwards.
Tippett says that, while he’s shown time travel to be mathematically possible, we just don’t have the materials – something he and his colleagues call “exotic matter” – to get the job done. They haven’t even been discovered, yet.
Either way, I figure, if we ever do travel through time, black holes will be involved. Not just because of John Titor’s old time travel story, but also ideas like this and the possible existence of something like Kerr black holes.
They just seem to be the way to go.