How does one conclude a book about time travel, about the heterochronic function of time machines, at a moment when fascist politics are resurgent in the US and across the globe, and a range of catastrophic arcs, from the social to the planetary, reach into the present from different zones of the future? One imagines Walter Benjamin's angel appearing on these horizons and importuning us to pull the emergency brake on history as it barrels forward. But which track are we on? Ernst Bloch thought that there could be no ‘proletarian hegemony’ without the ability to master ‘the substance of genuine non-sametimeliness and its heterogeneous contradictions’. For some thinkers, this exhortation in 1935 was ineffectual in countering ‘fascism's political exploitation of “nonsametimely” social elements and cultural strata’ with what Bloch envisioned as a ‘Triple Alliance of the proletariat with the impoverished peasants and the impoverished middle classes’. The idea that the left could marshal the forces of non-synchronous and synchronous contradiction – the oppositional power of those who have been left behind in an unfinished past and those whose antagonism comes directly from contemporary relations of production in the dominant socio-economic order – was, as Peter Osborne says, ‘already too late’.

We currently see more clearly that our present is simultaneously ‘archaic, modern, and futuristic’, and that ‘every historical era is likewise multitemporal […] with multiple pleats’. Michel Serres's angels fly across and between the pleats in order to understand different kinds of assemblages, which has given rise to accusations that his history is not historicist, that he pilots a time machine. But I imagine that his angel and time machine have learned the lesson of the backward-facing Angelus Novus. These heterochronic devices do not abandon the ‘revolutionary chance in the fight for the oppressed past’, but rather add to their operations a scaling-up of historiographic replay and, crucially, a forward-facing scan for trajectories already running through what we take as the present. Like the fantasy of moving within the fifth-dimensional bulk, the task of disclosing, tracking and engaging de-synchronised timelines always takes place from another reference frame that is itself shot through with zones of differential pace and timelines of varying length.