Pierre-Simon Laplace
In Our Time: Science
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The Nebula Hypothesis
The nebula hypothesis is Laplace's approach to answering another puzzle about the solar system. All of the planets that were known then, and indeed all the ones that are known now, were going around the sun in the same direction. There didn't seem to be any particular reason why they should all go around in the same way. So he calculated how likely was it that this had happened by chance. The probability that it was happening by chance was less than one over 29-2s multiplied together. And so because the planets were being thrown off by this rotating ball of what he thought was liquid at the time, everything would wind up going in the same directions.
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