Imagine building a device that could send a fully functioning facsimile of your own self into the past. You would put right some of the things you got wrong, wouldn't you! Nothing could go wrong, could it? You couldn't make things worse, could you? You could just use it for sightseeing maybe. See first-hand history being made. You would be a bystander having no effect on history so no danger there then. Oh but wait, do all plans turn out right? What...