Time travel is not possible

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

Feel free to disagree and/or flame!

Logically I came up with this:

Time is man made, its a messurment of movement. EI the full distance at wich the sun moves in motion. Its day time because of the position of the sun. ect.

Old clocks used the movement of various devices (pendulum and gears) to keep time.

Todays clocks use crystal oscillators, wich still operates as the same principle as the old clocks.

the distance it takes an object from point A to point B and or back. May equal "time".

I can't really fathom and existing demension of "time" or an actual element of "time".