In this episode of “What Is X?” Justin E.H. Smith and Emily Thomas tackle the timely yet timeless question: "What is time?" Is time an external, objective fact, or is the flow and tempo of the world internal to us—in some sense, all in our head? Could a robot have consciousness even if it didn't understand time? To help concretize these potent questions, Justin and Emily look back at the thought of a now mostly-obscure metaphysician by the name of J.M.E. McTaggart, who argued that time was unreal. In doing so, however, he proposed a framework for time that philosophers have taken up enthusiastically ever since: either one must believe that time is purely linear—occurring as a series of discrete moments in sequence, plotted out on a timeline, simply past or future—or that there is some special interval we might call the "present," in addition to the past and future. Since McTaggart's time, philosophers have been excitedly proclaiming themselves either A theorists (partisans of the present) or B theorists (team pure past and future). Listen in to find out which identity Justin and Emily claim for themselves! Throughout the hour, they also touch on Leibniz and Aristotle's notions of temporality, Adorno on the spatialization of time, and why the ancient Greeks could dream up many notions we'd now think of as sci-fi, but the one thing that seemed to exceed their imagination was time travel.