Somebody has to make the obvious Star Trek reference here so I guess it might as well be me: there was an episode of TNG once where the Enterprise kept being destroyed over and over again, and the only way they were able to "tell themselves" of impending doom was to send messages "back" informing the "new past" about the "forthcoming future." Interesting that this article should articulate this distinction of "messages" vs. even the <i>possibility</i> (theoretical or otherwise) of physical human time travel.