Reasoning About the Future: Doom and Beauty.

Publication Year:
Usage 373
Downloads 373
Repository URL:
Dieks, Dennis
preprint description
According to the Doomsday Argument we have to rethink the probabilities we assign to a soon or not so soon extinction of mankind when we realize that we are living now, rather early in the history of mankind. Sleeping Beauty finds herself in a similar predicament: on learning the date of her first awakening, she is asked to re-evaluate the probabilities of her two possible future scenarios. In connection with Doom, I argue that it is wrong to assume that our ordinary probability judgements do not already reflect our place in history: we justify the predictive use we make of the probabilities yielded by science (or other sources of information) by our knowledge of the fact that we live now, a certain time before the possible occurrence of the events the probabilities refer to. Our degrees of belief should change drastically when we forget the date---importantly, this follows without invoking the ``Self Indication Assumption''. Subsequent conditionalization on information about which year it is cancels this probability shift again. The Doomsday Argument is about such probability \textit{shifts}, but tells us nothing about the concrete values of the probabilities---for these, experience provides the only basis. Essentially the same analysis applies to the Sleeping Beauty problem. I argue that Sleeping Beauty ``thirders'' should be committed to thinking that the Doomsday Argument is ineffective; whereas ``halfers'' should agree that doom is imminent---but they are wrong.