Time travel is not possible

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

Feel free to disagree and/or flame!

How do you control where you end up in the other time?  We don't know of an absolute reference point to work with.  If you go to last week, well last week the Earth was at a different place in space relative to anything outside the Earth.

Do you need to house a special beacon that exists in all time so that you can be positioned relative to it no matter what time you go to?  How the hell do you manage to set up the beacon in the past in the first place?  The best you can do is build it now and use it for as long as it can stay put.