Pierre-Simon Laplace quotes

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Pierre-Simon Laplace. (1749 – 1827). French mathematician, statistician, engineer, physicist, astronomer, and philosopher.

System of Nature

“The present state of the system of nature is evidently a consequence of what it was in the preceding moment, and if we conceive of an intelligence that at a given instant comprehends all the relations of the entities of this universe, it could state the respective position, motions, and general affects of all these entities at any time in the past or future. Physical astronomy, the branch of knowledge that does the greatest honor to the human mind, gives us an idea, albeit imperfect, of what such an intelligence would be. The simplicity of the law by which the celestial bodies move, and the relations of their masses and distances, permit analysis to follow their motions up to a certain point; and in order to determine the state of the system of these great bodies in past or future centuries, it suffices for the mathematician that their position and their velocity be given by observation for any moment in time. Man owes that advantage to the power of the instrument he employs, and to the small number of relations that it embraces in its calculations. But ignorance of the different causes involved in the production of events, as well as their complexity, taken together with the imperfection of analysis, prevents our reaching the same certainty about the vast majority of phenomena. Thus there are things that are uncertain for us, things more or less probable, and we seek to compensate for the impossibility of knowing them by determining their different degrees of likelihood. So it was that we owe to the weakness of the human mind one of the most delicate and ingenious of mathematical theories, the science of chance or probability.”
  • Source: Pierre-Simon Laplace, 'Recherches, 1º, sur l'Intégration des Équations Différentielles aux Différences Finies, et sur leur Usage dans la Théorie des Hasards' (1773, published 1776). In Oeuvres complètes de Laplace, 14 Vols. (1843-1912), Vol. 8, 144-5, trans. Charles Coulston Gillispie, Pierre-Simon Laplace 1749-1827: A Life in Exact Science (1997), 26.

Problems of Probability

“The most important questions of life... are indeed for the most part only problems of probability. Strictly speaking it may even be said that nearly all our knowledge is problematical; and in the small number of things which we are able to know with certainty, even in the mathematical sciences themselves, the principal means for ascertaining truth — induction and analogy — are based on probabilities.”

No Need Hypothesis

“I had no need of that hypothesis.”
  • Source: Pierre-Simon Laplace in conversation with Napoleon Bonaparte circa 1802 (spoken in French). The statement is in response to Napoleon's question as to why Laplace did not write about the creator in his books. The conversation is recounted in a diary entry by astronomer William Herschel dated August 8, 1802. A published account of the conversation is found in the book ‘A Short Account of the History of Mathematics’ by W. W. Rouse Ball, 4th edition, published 1908. Statement translated from French “Je n'avais pas besoin de cette hypothèse-là”.