I don't think that travel into the future is a mere fantasy. Going into a time period that does not yet exist may seem out-wordly when all it takes is the passing through a much faster moving plane or realm so to speak.

Time travel into the future is most more probable than going into the past. Using Einstein's theory, if a spaceship/machine were able to achieve speeds near or equal to the speed of light, time in the machine would go much slower. The closer you are to achieving lightspeed, the slower time on the rest of the material plane will go. The only problem is that according to Einstein's theory, achieving half the speed of light will half your volume, while acheiving the full speed of light will turn our bodies and whatever we are traveling in, into a wave.