Pierre-Simon Laplace (March 23 1749 - March 5 1827) was a French mathematician, the discoverer of the Laplace transform and Laplace's equation. He was a believer in causal determinism.

One curious formula for the probability that the sun would rise was given by Laplace. He claimed that this probability was , where d is the number of days that the sun has risen in the past. Laplace claimed that this formula, known as (Laplace) Rule of Succession, applied in all cases where we knew nothing, or where what we did know was swamped by what we didn't. It is still used as an estimator for the probability of an event if we know the event space, but only have a small number of samples.

Laplace strongly believed in causal determinism, which is expressed in the following citation:

"We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at any given moment knew all of the forces that animate nature and the mutual positions of the beings that compose it, if this intellect were vast enough to submit the data to analysis, could condense into a single formula the movement of the greatest bodies of the universe and that of the lightest atom; for such an intellect nothing could be uncertain and the future just like the past would be present before its eyes."

This intellect is often referred to as Laplace's demon. The discoveries of modern physics, especially quantum physics (see uncertainty principle) proved that the existence of such an intellect is not possible even in principle.

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