Huffington Post: In the first "Back to the Future" movie, all it took to travel through time was 1.21 gigawatts and a flux capacitor (packed into a DeLorean sports car for style points). Despite centuries of dreams and decades of bona fide research, flux capacitors remain beyond our grasp, as do any other time travel-enabling devices.
From a pure physics point of view, travel into the future is not at all impossible and in fact happens all the . . . time. With all due respect to Doc Brown, however, backward time travel stacks up as a much tougher proposition.