There is some already said intimation of this happening, to where a witness on a super highway has seen a land vehicle shaped similar to an elongated bus-like football, that was silver and had people in it looking out of portholes.This was in The Encyclopedia Of Space Time And Mind complete with a drawing.Other than this one claim, I feel that time travel will eventually become closely regulated.This is similar to a very tall tower to where the people now living at the top of the tower can dive down underwater and take stones from the near base of the tower as souvenirs.If they were allowed to keep doing do, then the foundation allowing the tower to stand would degrade, making the entire structure collapse in upon itself.Pinter