Time travel is not possible

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

Feel free to disagree and/or flame!

Time is an arbitary, artificial frame of reference.

It wasn't even established in the physical world until relatively recnetly when they attatched it to the vibrations of a particular molecule.

Without a solid point of reference, it'd be impossible to do any sort of 'traveling' since you'd have no measure of how far you've traveled or in which direction. Kind of like driving on a totally unfamiliar freeway system with no signs or any other method of getting your bearings. Even if you could move on the road, you'd have no way of telling where you are.