On aliens, inductive risk, and disappointing my earlier self

This is evidence for the hypothesis that I am not a cartoonist, a conclusion which would be a great disappointment to my third-grade self.1

A philosopher might write a ponderous paragraph like this:

[C]onsider the search for extraterrestrial intelligence (SETI). Let P be the proposition that there is intelligent life on some other world which could be detected by a systematic SETI project. Direct evidence for P is lacking. … However, it is plausible to think that SETI would be pursued with greater vigor and ingenuity by scientists who believe P. Since alleged alien signals should not be accepted too readily, it would be good to have some scientists who believe ∼P and who would subject the signals to critical, sceptical scrutiny. So the community might maximize its chances of identifying alien civilizations (if there are any) by having some members who already think that there are (or probably are) such civilizations and others who already think that there are (or probably are) none.

A cartoonist, on the other hand, might draw something like this:

XKCD cartoon displaying different degrees of caution in response to evidence of alien life.


The fact that the philosopher and cartoonist both have degrees in physics makes this as perfect a natural experiment as one could hope for.3

  1. Evidence against the hypothesis is old and inconclusive.
  2. Copyright Randall Monroe and used under a CC by-nc 2.5 license.
  3. Besides being in different media, the two are making different claims. The cartoonist suggests that there’s a level of caution which is appropriate for all scientists, whereas the philosopher claims that it’s best for the community if individual scientists react with different levels of caution. End pedantic footnote.

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