Back to the Future

Axel and I were watching the German possible-worlds scenario film Run Lola, Run when we got to thinking about time-travel. Naturally, our discussion required that we accept a common sense, spatialized conception of time, if only to give the screenplay writers a fighting chance; reading Bergson and listening to Elusive-Hyphen's diatribes against "Hollywood's obsession with time-travel" made this fairly difficult.
Axel's opening view was that, if we accept a strong determinism, then it is not inconceivable that our irruption into the causal chain, when we go back in time, is always already part of the 'causal account'. That is to say, our actions as a time-traveller in 1975 would be determined, but determined by states of affairs in 2006.
I objected by saying that, given our assumptions (ie, our commonsensical, simple-science fatalism), a problem arises because, from these very assumptions, it follows that the state of affairs in the world at any moment is determined by that of the prior moment. And since on our simple model time unfolds in a 'straight-line', we encounter the same difficulty as Kant did on the question of free will: how does anyone, or anything, intervene in the causal chain, since causal determinism is true a priori (or in our case, by definition)?
To clarify - my problem with time-travel has to do with the magical appearance, in the causal order, of undetermined events, even though we know that they are determined by events in the future. To accept this outlook, we must adopt the view that all of history is simultaneous. The problem now is that our claim that 'every state of affairs is caused by the state of affairs immediately prior' loses all meaning, since we have no way in which to grasp such a temporal understanding of causality.

Our concerns developed from thinking about what would happen if you travelled back in time and murdered the 'young you'. Would the later 'you' simply evaporate? Would you find it impossible to kill the 'younger you'? These are pressing questions. But I think it is high time I recommend taking a look at Bergson ('how is forgetting possible?').