FTL and time travel

[KvickFlygarn87]

Due to relative time changing when an object moves near-c, would time travel not be possible?

And if so, could you go lightspeed backwards to go the other way? (I'm kidding, don't you pull out your vectors just yet! ;-))

[K^2]

If I recall correctly, two objects that are traveling faster than light and can communicate with eachother can allow for time travel. But such possibilities are almost always excluded for reasonable FTL setups. So the only way to time-travel still remains traversing a closed space-time loop. Though, FTL can allow you to traverse some paths that you could not otherwise.

Anything sub-light preserves the causality.

[Warhorse]

Time passes more slowly at high speeds and in strong gravity, so you could certainly travel forward in time. IIRC there are solutions to the relativity equations which imply the possibility of traveling backwards in time as well, but the conditions for realizing them IRL are sufficiently ... tricky ... that nobody has (yet) demonstrated them.