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Xkcd’s one of our favourite web comics, but did you know the bloke behind it, Randall Monroe, is one smart cookie? He’s launched a new site called “What If?” that’ll answer all your weird and wonderful hypothetical questions with physics, every Tuesday.
So, every Tuesday, Monroe will answer someone’s hair-brained question, which anyone can submit, with detailed physics and classic xkcd-style illustrations. Apparently the site was kicked off because of the sheer number of these curious questions Monroe gets in his email every day, what better way to answer them?
If you’ve ever wondered what would happen if you tried to hit a baseball flying at 90 per cent of the speed of light, or other random hypothetical, never-going-to-happen questions that boggle the mind, drop by every Tuesday for another instalment, or ask a question of your own. [What If? via The Next Web]
Great with physics, not so hot with statistics.
The current question relates to answering the SAT questionnaire randomly and getting them all right.
The chances are very very very^lots unlikely.
Mr Monroe assumes that that means that this wouldn’t happen for billions of attempts/years.
However, it is equally unlikely to happen on each attempt.
So it could equally happen each time – so it’s as likely to happen the first attempt as the last.
He’s not saying that that isn’t the case.
He’s just considering the cumulative probability of getting the SAT right once by guessing it randomly, which makes perfect sense, precisely assuming that it’s equally unlikely to happen on each attemp.
He’s doing that, but then expressing it (wrongly) in terms of time.
So that “it will happen one time in a billion years” becomes “it will not happen until a billion years has elapsed”.
Which is not the same thing at all.
It might happen tomorrow, and then not for a very long time.
It might happen in a billion years.
It might happen tomorrow and then the next day, and then not for a really really long time.
Probability is not prediction.
Not to be a pedant, but Xkcd with a capital X just looks wrong
This is actually what his critics have been saying he should do for a while – an illustrated blog without the usual ‘must be funny’ constraint of a comic (which IMO has produced a few uninspired ones).