The epistemic challenge to longtermism

Abstract

Longtermism argues what we ought to do is mainly determined by effects on the far future. A natural objection is that these effects may be nearly impossible to predict—perhaps so close to impossible that, despite the astronomical importance of the far future, the expected value of our present options is mainly determined by short-term considerations. This paper aims to precisify and evaluate this epistemic objection. To that end, it develops two simple models for comparing “longtermist” and “short-termist” interventions, incorporating the idea that, as we look further into the future, the effects of any present intervention become progressively harder to predict. These models yield mixed conclusions: If we simply aim to maximize expected value, and don’t mind premising our choices on minuscule probabilities of astronomical payoffs, the case for longtermism looks robust. But on some prima facie plausible empirical worldviews, the utilitarian case for longtermism depends very heavily on minuscule probabilities of astronomical payoffs. – AI-generated abstract.