Does Time-Symmetry Imply Retrocausality? How the Quantum World Says "Maybe"

Understand

It has often been suggested that retrocausality offers a solution to some of the puzzles of quantum mechanics: e.g., that it allows a Lorentz-invariant explanation of Bell correlations, and other manifestations of quantum nonlocality, without action-at-a-distance.

• Some writers have argued that time-symmetry counts in favour of such a view, in the sense that retrocausality would be a natural consequence of a truly time-symmetric theory of the quantum world.
• Critics object that there is complete time-symmetry in classical physics, and yet no apparent retrocausality.
• Why should the quantum world be any different? This note throws some new light on these matters.