Yeah and then you just need to accelerate to 88 MPH :D
Ok, I love that movie, in fact Back to the Future is one of my favories.
But my question is somewhat serious.
Imho time travel maybe possible but only for traveling to the past. I think future isn't determined yet so you cannot go there. On the other hand, going to the past and changing only a minor thing can lead to huge effects on the present. Just is you go to the past, you've already changed it.
You know the chaos theory. :)

Anyway wether it is possible or not I think time travel remains in the world of sf for a couple more centuries.