No Need of That Hypothesis

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

The line is one of the most quoted in the history of science: Napoleon, reportedly leafing through Laplace's Mecanique Celeste, asked why God appeared nowhere in an account of how the solar system holds together, and Laplace answered that he had no need of that hypothesis. It is a good story and a plausible one; it fits everything else known about Laplace's method, which treated a cause as something to be established by evidence rather than assumed for comfort, most famously in the probability calculus he built to formalize exactly that kind of reasoning about causes from effects. But the anecdote comes down through secondhand retellings by contemporaries, not through anything Laplace wrote in his own hand, so its precise wording cannot be checked against a primary source. What can be checked is the substance behind it: Laplace had in fact shown, across decades of work, that the wobbles and near-instabilities in planetary orbits that earlier astronomers worried might require divine correction were self-correcting on strictly mechanical grounds. Whatever he actually said to Napoleon, that was the argument he had already made in print, at length, without needing a punchline to make the point.