Quantum mechanical model of a time travel paradox

Abstract

The retrocausality inherent in the retrodictive description of a quantum optical device called the quantum scissors allows this device to be used as a non-deterministic time machine. We show that the device can be used to model the time travel paradox of retrospective suicide. Here a man goes back in time and interferes with his own birth, weakening his infant self in such a way that he is killed by the time machine and is unable to interfere with his own birth. We find that the paradox is avoided by interfering quantum mechanical amplitudes making the time travel event impossible in this case. A slight modification that limits the interference with the birth so that the infant is only injured by the time machine to give a self -consistent cycle does, however, render the time travel event possible. This lends support to the idea that time travel is only possible if it yields a self-consistent cycle that avoids a paradox.