By Wiki's definition, no its not possible, but by my definition it is in ONE direction, not both. It is possible to go forward in time, which was proven by Einstein. By putting an atomic clock in a satellite, which was matched up with another one of his atomic clocks, moving at high speeds around the Earth, when the clock was retrieved, it was several seconds slower than the one on Earth. This showed that the clock in the satellite aged slower than the one on Earth, proving his thoery that, at speeds close to the speed of light, hundreds of years will go by feeling like seconds to the traveler. You also shrink alot when you go that fast. So traveling into the future? Possible! Traveling to the past? ... Not so much :(
Traveling to the past is possible under the same theory as allows the travel you just talked about.