Commenter Ray Penver writes:

Hi, PP! It’s me again
I wonder what would be your estimation of Isaac Newton’s IQ.
I know quite a bit about his life.
He’s considered the best physicist and scientist ever, one of the best mathematicians ever and one of the most influential people, too.
So, what do you think?

Newton’s IQ is fascinating because not only is he considered the best physicist of all time, but according to Michael Hart’s book The 100, the second most influential person of all time; though one led to the other. These aren’t independent achievements,

So what was his IQ?

According to this source, 60.5 billion people have lived from 1 AD to 2011. Let’s say 16% were white. Assuming Newton was the best physicist to ever live, he would have at the very least been at the one in 9.68 billion level among whites, which is +6.33 standard deviations (SD) on a normalized curve.

However great achievement requires more than just ability. It also helps to have 10,000 hours of practice, among other things. Ability seems to explain 66%  to 70% of the variance in various cognitive performance, suggesting ability correlates 0.82 with performance.

So if Newton were +6.33 SD in physics performance, we’d expect him to be 0.82(+6.33) = +5.19 SD in physics ability.

How much does physics ability correlate with IQ? The math section of the WIAT correlates 0.84 with WAIS-IV full-scale IQ, so if Newton were +5.19 SD in physics ability, I’d expect him to be 0.84(+5.19 SD) = +4.4 SD in IQ. In other words, I’d expect him to have scored IQ 166 (white norms) on a random test normed in his day.

To appreciate how high that is, young white American men have an average height of 5’10.1″ (SD = 2.94″) so an IQ of 166 is the height equivalent of being 6’11”. Both are +4.4 SD.

So just as we might expect the greatest basketball player of all time to be 6’11”, we’d expect the greatest physicist of all time to be IQ 166.

To those who think even IQ 166 is not high enough for a mind as great as Newton, I point to examples of other great minds who scored much lower on IQ tests such as Ted Kaczynski in adulthood or Garry Kasparov. For those who say the tests weren’t valid measures of their intelligence, I say IQ is an imperfect science. An IQ score is simply one’s performance on highly g loaded psychometric tasks not a direct measure of neurological functioning, so occasionally it will give highly flawed results. IQ 166 is simply my best guess of how Newton would have scored on a randomly selected high ceiling IQ test considered valid in his time and place, not necessarily a prediction of his actual intelligence.

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