According to Einstein's theory, it should be possible to go forward in 'time'.
According to the theory, time is related to speed, (not the chemical, although it might also change ones perception of time, don't know for sure) if a person was able to travel at the speed of light, then the traveler’s local time would stop, and the time in the rest of the universe would continue at the normal rate.
If a traveler could adjust the travel speed so that every minute of his time would equal a year in Earth time, then he could choose how many years into the future he wishes to go simply by looking at his watch and slowing down at the desired moment.
Coming back from the future would be trickier. I do not know if; by traveling faster than light would take you back to the time frame that you originally left from. Perhaps, by traveling faster than light you would only have the ability to see how things used to be, sort of like looking at a star that is thousand light years away and seeing how it looked thousand years ago.

All we need to do is figure out how to travel faster than light, then we can take a quick trip and see what happens ;-)

Happy trails

Johannes