Having recently written a post about the future, I thought that I might add my two cents concerning time travel.
According to Einsteining physics, we are all moving at the speed of light. Me, you, the tree outside my window - even an ant that I squashed underfoot earlier today in an act of clumsy non-Buddhist apathy. But before you all start jumping up and down and clicking on the comments box to inform me (politely) that nothing, save light, travels at 300,000 km every second I will also inform you that movement can occur in any of a number of dimensions. One of those dimensions is time.
If you picture a graph, the vertical axis of which represents the spatial dimensions and the horizontal axis of which represents the temporal, you can imagine the manner in which such movement may be plotted. We snail-like organisms who crawl through life at a paltry fraction of the speed of light do virtually all of our movement on the horizontal axis. The pilot of the jetplane (itself also moving at a miserable fraction of the Einsteinian "constant") does his movement almost entirely through time, as does the chair that I am sitting on and the dog running happily down the street. Light, on the other hand, does all of its movement through space. It travels so quickly that, on the horizontal axis, it does not move at all.
You heard me correctly. Particles of light ("photons") do not age. We age rapidly but, as Einstein also explained, movement through both space and time is entirely relative. That is to say that if I hopped on a hypothetical space-ship and zipped through the galaxy at speeds approaching those of light, even though the earth and all that is in it would have aged significantly beyond me by the time that I returned, I would not have experienced the slow passage of time felt by those that I had left behind me.
There is a curious practical element to all of this. Time travel, in one direction only, is actually a feasible possibility - so long as scientists can devise a way to speed up a craft to a sizeable fraction of the speed of light. Should that be possible then the occupant of that craft can move themselves as many years into the future as they so desire, simply by inhabiting it while it moves rapidly throughout space.
The downside: as I mentioned before, the future is not a place. There is no guarantee whatsoever that the world that will greet this occupant upon their exit from this craft will be anything other than a less familiar version of the one that they had left behind - now minus their families and friends. And, of course, there is no way to go back.