While I disagreed with your other comment, I’m inclined to agree with this one. “The amount of people to ever live” feels like a rather arbitrary and ill-defined number, and the argument’s Wikipedia article has a number of objections which I agree with and which follow similar lines: we don’t know that the number of people to ever live is necessarily finite, human population seems more likely to be exponentially than uniformly distributed, and the whole argument gets rather paradoxal if you apply it to itself.
It feels like the kind of thing that’s a solid argument if you accept its premises, but then there’s no particular to reason to expect that the premises would be correct.
Some philosophers have been bold enough to suggest that only people who have contemplated the Doomsday argument (DA) belong in the reference class ‘human’. If that is the appropriate reference class, Carter defied his own prediction when he first described the argument (to the Royal Society). A member present could have argued thus:
Presently, only one person in the world understands the Doomsday argument, so by its own logic there is a 95% chance that it is a minor problem which will only ever interest twenty people, and I should ignore it.
If the DA’s lifetime is governed by the principle of indifference and the Copernican principle then based on the length of its current existence, and assuming that it is randomly drawn from a reference class of probabilistic speculations it is 95% certain that it will be refuted before the year 2500.
If the DA is not itself subject to these principles then its assumption that the human race’s survival-time can be modeled using them appears to be a paradox (to Lansberg & Dewynne).
Hm, interesting. It is a bit unfair to talk about what the first person to formulate the doomsday argument could have used it to predict, for the same reason it is unfair to talk about what the first people to exist could have used the doomsday argument to predict: being the person who comes up with an idea that becomes popular is rare, and we expect probabilistic arguments to fail in rare edge cases. Also, the self-referencing doomsday argument rebuttal offers a counter-rebuttal of itself: It is more recent and has been considered by fewer people than the doomsday argument has, so it will probably have a shorter lifespan. (yes, I thought of the obvious counter-counter-rebuttal.)
The main point that I get out of those examples is that the Doomsday Argument is really a fully general argument that can be applied to pretty much anything. You can apply it to itself, or I could apply it to predict how many days of life I still have left, or for how long I will continue to remain employed (either at my current job, or in general), or to how many LW comments I am yet to write...
A claim like “my daughter just had her first day of school, and if we assume that she’s equally likely to find herself in any position n of her total amount of lifetime days in school N, then it follows that there’s a 95% chance that she will spend a maximum of 20 days of her life going to school” would come off as obviously absurd, but I’m not sure why the Doomsday Argument would be essentially any different.
It’s possible to argue that it is appropriate to use SIA in some of those examples, but SSA for the duration of the human race.
“my daughter just had her first day of school, and if we assume that she’s equally likely to find herself in any position n of her total amount of lifetime days in school N, then it follows that there’s a 95% chance that she will spend a maximum of 20 days of her life going to school”
The doomsday argument doesn’t say that, even if you do use SSA with the reference class of days that your daughter is in school. You’re confusing the likelihood of the evidence given the hypothesis with the posterior probability of the hypothesis given the evidence.
It feels like the kind of thing that’s a solid argument if you accept its premises, but then there’s no particular to reason to expect that the premises would be correct.
That summarized it better than I could. Thank you!
While I disagreed with your other comment, I’m inclined to agree with this one. “The amount of people to ever live” feels like a rather arbitrary and ill-defined number, and the argument’s Wikipedia article has a number of objections which I agree with and which follow similar lines: we don’t know that the number of people to ever live is necessarily finite, human population seems more likely to be exponentially than uniformly distributed, and the whole argument gets rather paradoxal if you apply it to itself.
It feels like the kind of thing that’s a solid argument if you accept its premises, but then there’s no particular to reason to expect that the premises would be correct.
I don’t understand. What does it mean to apply the doomsday argument to itself?
(from here)
(from here)
Hm, interesting. It is a bit unfair to talk about what the first person to formulate the doomsday argument could have used it to predict, for the same reason it is unfair to talk about what the first people to exist could have used the doomsday argument to predict: being the person who comes up with an idea that becomes popular is rare, and we expect probabilistic arguments to fail in rare edge cases. Also, the self-referencing doomsday argument rebuttal offers a counter-rebuttal of itself: It is more recent and has been considered by fewer people than the doomsday argument has, so it will probably have a shorter lifespan. (yes, I thought of the obvious counter-counter-rebuttal.)
The main point that I get out of those examples is that the Doomsday Argument is really a fully general argument that can be applied to pretty much anything. You can apply it to itself, or I could apply it to predict how many days of life I still have left, or for how long I will continue to remain employed (either at my current job, or in general), or to how many LW comments I am yet to write...
A claim like “my daughter just had her first day of school, and if we assume that she’s equally likely to find herself in any position n of her total amount of lifetime days in school N, then it follows that there’s a 95% chance that she will spend a maximum of 20 days of her life going to school” would come off as obviously absurd, but I’m not sure why the Doomsday Argument would be essentially any different.
It’s possible to argue that it is appropriate to use SIA in some of those examples, but SSA for the duration of the human race.
The doomsday argument doesn’t say that, even if you do use SSA with the reference class of days that your daughter is in school. You’re confusing the likelihood of the evidence given the hypothesis with the posterior probability of the hypothesis given the evidence.
That summarized it better than I could. Thank you!