Thursday, September 9, 2010  Backwards causation  It is commonly
thought that a cause C metaphysically cannot have an effect in
its past. I see two simple ways of making sense of this
principle in a relativistic framework:   1. A cause can only
have effects in the future half lightcone centered on it.   2. A
cause cannot have effects in the past half lightcone centered on
it. But I think neither of these is a plausible candidate for a
metaphysical principle. Consider what (1) and (2) respectively
say in a flat spacetime:   1. A cause at (x,t) can only have an
effect when the effect is at a spacetime location (y,u) such
that |xy|<c(ut).   2. A cause at (x,t) cannot have an effect at
a spacetime location (y,u) when |xy|<c(tu). But these just don't
seem to be plausible candidates for a metaphysical principle,
though I suppose one might think that they could be consequences
of a physical principle. The same applies to the more
complicated versions we'd need in a non-flat spacetime. If we
want (1) or (2) to be non