The doomsday example, as phrased, simply doesn’t work.
Only about 5-10% of the ever-lived population is alive now. Thus, if doomsday happened, only about that percentage would see it within our generation. Not 66%. 5-10%. Maybe 20%, if it happened in 50 years or so. The argument fails on its own merits: it assumes that because 2⁄3 of the ever-human population will see doomsday, we should expect with 2⁄3 probability to see doomsday, except that means we should also expect (with p=.67) that only 10% of the ever-human population will see doomsday. This doesn’t work. Indeed, if we think it’s very likely that 2⁄3 of the ever-lived will be alive on doomsday, we should be almost certain that we are not among that 2⁄3.
More generally, the 2⁄3 conclusion requires generational population tripling over many generations. This has not happened, and does not appear to be likely to happen. If 2⁄3 of the ever-lived were alive today, and there were reason to believe that the population would continue to triple generationally, then this argument would begin to make sense. As it is, it simply doesn’t work, even if it sounds really cool.
Incidentally, the wikipedia summary of the doomsday argument does not sound anything like this. It says (basically) that we’re probably around the halfway point of ever-lived population. Thus, there probably won’t be too many more people, though such is certainly possible. It does not follow from this that 2⁄3 of the ever-lived will be alive for doomsday; it only says that doomsday ought to happen relatively soon, but still probably several generations off.
I don’t object to the rest of the reasoning and the following argument, but the paraphrasing of the Doomsday argument is a complete straw man and should be dismissed with a mere googling of “world population growth.” I’m not sure that the logic employed does anything against the actual DA.
The doomsday example, as phrased, simply doesn’t work.
Only about 5-10% of the ever-lived population is alive now. Thus, if doomsday happened, only about that percentage would see it within our generation. Not 66%. 5-10%. Maybe 20%, if it happened in 50 years or so. The argument fails on its own merits: it assumes that because 2⁄3 of the ever-human population will see doomsday, we should expect with 2⁄3 probability to see doomsday, except that means we should also expect (with p=.67) that only 10% of the ever-human population will see doomsday. This doesn’t work. Indeed, if we think it’s very likely that 2⁄3 of the ever-lived will be alive on doomsday, we should be almost certain that we are not among that 2⁄3.
More generally, the 2⁄3 conclusion requires generational population tripling over many generations. This has not happened, and does not appear to be likely to happen. If 2⁄3 of the ever-lived were alive today, and there were reason to believe that the population would continue to triple generationally, then this argument would begin to make sense. As it is, it simply doesn’t work, even if it sounds really cool.
Incidentally, the wikipedia summary of the doomsday argument does not sound anything like this. It says (basically) that we’re probably around the halfway point of ever-lived population. Thus, there probably won’t be too many more people, though such is certainly possible. It does not follow from this that 2⁄3 of the ever-lived will be alive for doomsday; it only says that doomsday ought to happen relatively soon, but still probably several generations off.
I don’t object to the rest of the reasoning and the following argument, but the paraphrasing of the Doomsday argument is a complete straw man and should be dismissed with a mere googling of “world population growth.” I’m not sure that the logic employed does anything against the actual DA.