摘要：SummarySocial dilemmas are often shaped by actions involving uncertain returns only achievable in the future, such as climate action or voluntary vaccination. In this context, uncertainty may produce non-trivial effects. Here, we assess experimentally — through a collective risk dilemma — the effect of timing uncertainty, i.e. how uncertainty about when a target needs to be reached affects the participants' behaviors. We show that timing uncertainty prompts not only early generosity but also polarized outcomes, where participants' total contributions are distributed unevenly. Furthermore, analyzing participants' behavior under timing uncertainty reveals an increase in reciprocal strategies. A data-driven game-theoretical model captures the self-organizing dynamics underpinning these behavioral patterns. Timing uncertainty thus casts a shadow on the future that leads participants to respond early, whereas reciprocal strategies appear to be important for group success. Yet, the same uncertainty also leads to inequity and polarization, requiring the inclusion of new incentives handling these societal issues.Graphical AbstractDisplay OmittedHighlights•Timing uncertainty influences experimental observations in the collective risk game•It induces subjects to contribute earlier and in a polarized manner•Successful players adopt reciprocal strategies, responding in kind to past actions•Coordination gets more difficult under high timing uncertaintyBehavioral Neuroscience; Data Analysis; Decision Science
