Over at “Tapped”:http://www.prospect.org/weblog/archives/2005/06/index.html#006936 Matthew Yglesias links (tounge-in-cheek) to the SEP’s entry on “backwards causation”:http://plato.stanford.edu/entries/causation-backwards/, with some sarcastic suggestions for how Bush’s defence of the war in Iraq might look better if backwards causation were plausible. I don’t want to enter into the politics of this, but there is something odd about the Stanford piece.

As Matt says, in the debate about backwards causation _as such_, the main defender of the coherence of the view is Michael Dummett. But surely there are many more defenders of this view, namely all the defenders of the coherence of time travel. (Of which, as “the SEP also notes”:http://plato.stanford.edu/entries/time-travel-phys/, there are quite a few.)

Well, maybe not. Here’s the entry on backwards causation again.

bq. The idea of backward causation should not be confused with that of time travel. These two notions are related to the extent that both agree that it is possible to causally affect the past. The difference, however, is that time travel involves a causal loop whereas backward causation does not. Causal loops for their part can only occur in a universe in which one has closed time-like curves. In contrast, backward causation may take place in a world where there are no such closed time-like curves. In other words, an ordinary system S taking part in time travel would preserve the temporal order of its proper time during its travel, it would keep the same time sense during its entire flight (a watch measuring S’s proper time would keep moving clockwise); but if the same system S were to become involved in a process of backward causation, the order of its proper time would have to reverse in the sense that the time sense of the system would become opposite of what it was before its back-in-time travel (the watch will start to move counter-clockwise). So neither backward causation nor time travel logically entails each other and time travel is distinct from back-in-time travel.

This seems to me mistaken on several fronts. First, time travel does not _logically_ require closed time-like curves. Plenty of time travel defenders (e.g. Lewis) defend the coherence of sci-fi style ‘jumps’ from one time to an earlier time. This is not scientifically plausible, for several reasons, but then neither is backwards causation. (Except, I should add, in quantum cases where backwards causation might explain the Bell inequality.) Second, there’s no reason to say that backwards causation need be a process. Dummett’s original example was the rain dance on Wednesday causing the rain on Tuesday (or something like this – I don’t have the book in front of me). Backwards causation might be event causation, not process causation. Third, we might have backwards causation along one kind of process, even while we have forward causation in others. Imagine a case where some coffee ‘despills’ from the floor to the coffee cup, but all the while cools down as coffee does at room temperature. It doesn’t have its ‘personal’ time reversed, but there is something we’d generally call backwards causation going on. So I don’t really see why these cases should be treated apart, and these debates kept separate.