Why retrocausality — and why free will?
The 'classic' motivation for retrocausal models in QM stems from Bell's Theorem, and the nonlocality it seems to entail. Nonlocality is often felt to be counterintuitive in itself, and the source of an unresolved tension between quantum theory and special relativity. As Bell himself described the implications of his famous result: “[I]t's a deep dilemma, and the resolution of it will not be trivial ... [T]he cheapest resolution is something like going back to relativity as it was before Einstein, when people like Lorentz and Poincaré thought that there was an aether — a preferred frame of reference — but that our measuring instruments were distorted by motion in such a way that we could not detect motion through the aether.''
As Bell was well aware, the dilemma can be avoided if the properties of quantum systems are allowed to depend on what happens to them in the future, as well as in the past. Like most researchers interested in these issues, however, Bell felt that the cure would be worse than the disease — he thought that this kind of “retrocausality” would conflict with free will, and with assumptions fundamental to the practice of science. (He said that when he tried to think about retrocausality, he “lapsed into fatalism”.)