Doomsday Argument

The structure of the argument

First proposed by Carter (1983) and refined by Leslie (1990), the argument relies on Bayes' theorem. Consider two hypotheses: humanity ends after 200 billion people in total, or it continues to 200 trillion. If your birth rank is roughly the 100 billionth, that rank is far more likely under the small-population hypothesis, so after observing it the probability of the small hypothesis rises sharply. It is like drawing ball number 7 from one of two urns, one holding 10 numbered balls and the other a million: the draw makes the 10-ball urn more likely. Nielsen (1989) independently offered a similar idea. Leslie (1996) argued that the reasoning raises the prior probability of risks such as nuclear war and environmental crises.

Gott's delta t argument

Gott (1993) applied the Copernican principle, that we occupy no special position, to time. If you observe something at a random moment, there is a 95% chance you are in the middle 95% of its lifetime, so you can infer that it will last between 1/39 and 39 times as long as it has already existed. He said he used this method on seeing the Berlin Wall in 1969 to predict when it would fall, and he estimated humanity's remaining lifespan the same way. Goodman (1994) criticized the approach for ignoring prior information, and Caves (2008) reassessed the rule's predictive performance. The debate also connects to the Fermi paradox and the simulation argument (Bostrom, 2003).

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Criticisms and the reference class problem

Dieks (1992) and later Olum (2002) argued that if you accept the self-indication assumption, under which a world with more observers makes your own existence more likely, this effect exactly cancels the doomsday shift. Bostrom (2002) systematically compared the self-sampling and self-indication assumptions and showed that either choice leads to strange conclusions. The reference class problem, deciding which group you count as a random sample from, whether all humans or all beings capable of probabilistic reasoning, also changes the conclusion dramatically. The same issues recur in the Sleeping Beauty problem (Elga, 2000). Others, such as Sowers (2002), object that birth rank is not a random sample at all. At bottom, it is a question of how to handle observation selection effects such as survivorship bias.

FAQ

What is the doomsday argument in simple terms?

If you assume you were born at an ordinary, unremarkable point among all humans, it's unlikely that vastly more people will be born after you than before you.

Does the doomsday argument predict human extinction?

No. It doesn't predict extinction at any particular date. It's a philosophical argument that tests how far you can use your own position as evidence in probabilistic reasoning, and many critics argue that assumptions like self-indication cancel its conclusion.

Sources reviewed: 2026-10-26

References

1. Carter, B. (1983). The anthropic principle and its implications for biological evolution. Philosophical Transactions of the Royal Society A, 310(1512), 347–363.
2. Leslie, J. (1990). Is the end of the world nigh? Philosophical Quarterly, 40(158), 65–72.
3. Leslie, J. (1996). The End of the World: The Science and Ethics of Human Extinction. London: Routledge.
4. Gott, J. R. (1993). Implications of the Copernican principle for our future prospects. Nature, 363(6427), 315–319.
5. Nielsen, H. B. (1989). Random dynamics and relations between the number of fermion generations and the fine structure constants. Acta Physica Polonica B, 20, 427–468.
6. Dieks, D. (1992). Doomsday—or: The dangers of statistics. Philosophical Quarterly, 42(166), 78–84.
7. Bostrom, N. (2002). Anthropic Bias: Observation Selection Effects in Science and Philosophy. New York: Routledge.
8. Bostrom, N. (2003). Are we living in a computer simulation? Philosophical Quarterly, 53(211), 243–255.
9. Olum, K. D. (2002). The doomsday argument and the number of possible observers. Philosophical Quarterly, 52(207), 164–184.
10. Goodman, S. N. (1994). Future prospects discussed. Nature, 368(6467), 106–107.
11. Caves, C. M. (2008). Predicting future duration from present age: Revisiting a critical assessment of Gott's rule. arXiv:0806.3538.
12. Elga, A. (2000). Self-locating belief and the Sleeping Beauty problem. Analysis, 60(2), 143–147.
13. Sowers, G. F. (2002). The demise of the doomsday argument. Mind, 111(441), 37–46.