Theory says yes; practicality says no. Thanks to Einstein time travel is possible. The easiest way is travelling very close to the speed of light. Achieve 99.5% close to light speed means that in 5 years you travel 50 years. Goodbye friends and family you left behind. The harder way is creating a wormhole, a device that can bend space and time, looping it on itself to go into the future or past. The energy required would rival the energy of the stars. Sorry Sci-Fi fans.