TheOtherDave comments on Yes, Virginia, You Can Be 99.99% (Or More!) Certain That 53 Is Prime - Less Wrong

38 Post author: ChrisHallquist 07 November 2013 07:45AM

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Comment author: philh 07 November 2013 02:30:15PM 7 points [-]

Christian apologist William Lane Craig claims the skeptical slogan "extraordinary claims require extraordinary evidence" is contradicted by probability theory, because it actually wouldn't take all that much evidence to convince us that, for example, "the numbers chosen in last night's lottery were 4, 2, 9, 7, 8 and 3." The correct response to this argument is to say that the prior probability of a miracle occurring is orders of magnitude smaller than mere one in a million odds.

I'm not sure that response works. Flip a fair coin two hundred times, tell me the results, then show me the video and I'll almost certainly believe you. But if the results were H^200, I won't; I'll assume you were wrong or lying about the coin being fair, or something.

H^200 isn't any less likely than any other sequence of two hundred coin flips, but it's still one of the most extraordinary. Extraordinariness just doesn't feel like it's a mere question of prior probability.

Comment author: TheOtherDave 07 November 2013 03:01:35PM *  3 points [-]

Well, what's most interestingly improbable here is the prediction of a 200-coin sequence, not the sequence itself.

I suspect what's going on with such "extraordinary" sequences is a kind of hindsight bias... the sequence seems so simple and easy to understand that, upon revealing it, we feel like "we knew it all along." That is, we feel like we could have predicted it... and since such a prediction is extraordinarily unlikely, we feel like something extraordinarily unlikely just happened.