There’s a tantalising R-rated premise at the centre of the PG-13-rated sci-fi thriller Voyagers. In the future, the Earth is slowly becoming uninhabitable (something that’s depressingly less fiction and more science) and so a crew is assembled, by a muted Colin Farrell, to travel to another planet to check for viability, a familiar set-up given a novel spin. Because of the length of the journey –...