Time travel is not possible

If it is, we will have been visited by time travelers.

Feel free to disagree and/or flame!

As 3 dimensional beings we have a fixed movement through time that cannot be changed, but where we are moving can be. It could be possible to move backwards through time, or, in having our paths disrupted through a higher dimension than time, our paths could fall along far removed paths of time than it would ordinarily be. If we can control or alter our movement through the fifth dimension, time travel is possible.

But maybe, we already know how to do it. Has anyone ever considered that the reason for the lengthening lifespan of humans isn't better living conditions and medicine and such, but simply that we've been accelerating through time, skipping it, and having our natural existence in time extended.