Philosophers find talk of “changing the future” strange because the future is by definition not present and something cannot be changed unless it is already present. Depending on whether you are one of history's agents or spectators, the future is either just made up as you go along or just happens as it happens. The future cannot be made over again simply because it has yet to happen. But now let us remove the straitjacket of philosophical semantics from this discussion and think about the locution a bit more creatively. “Changing the future” suggests that one might travel to some time in the past and alter it so that what follows is other than what we know it to have been. Someday time travel technology may enable us to do just that in a relatively full-bodied way, as depicted in the remarkable CBS television series, The 4400, which ran for four seasons before falling foul of the great Writers Guild of America strike of 2007. The “4400” in the title refers to the number of people who have been taken by the future from the past to be biomedically retrofitted in various ways so that, once reinserted into the present, they might alter history so as to prevent the environmental catastrophe that in the future is destroying humanity.

However, as was observed in Chapter 2, the results of such retro-interventions need not make matters better. Thus, The 44000s driving plot device was the perpetual need to check the outcomes of future retro-interventions for purposes of acting in the present.