Time?

[Fisticuffs]

Time is just a name and unit of measurement which, like all systems of measurement, has no meaning to us unless associated with the entity being measured(100 pounds, yes...but of what?). We base our units on this profoundly infinite thing on things we can comprehend, like the earth circling the sun or the earth rotating on its axis; we do much the same when we divide the whole infinite length and breadth of space to the length of one's foot. We cannot describe time, only try to work with it.

Edit: Travel through time could conceiveably be possible if our minds were capable of wrapping around the concept of how...well, how we lived in relation to such an entity. We're born with an inherent knowledge of how to function in three dimensions, we need only develop the logic as to the very nature of time in order to travel through it--in which case we wouldn't need machines to do so, we could alter our positioning in said dimension with a mere mental effort.