Longtermism holds that 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 (a version of) this epistemic objection. To that end, I develop two simple models for comparing ...
