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Henri Poincaré

75 quotes

“Le savant digne de ce nom, le géomètre surtout, éprouve en face de son œuvre la même impression que l'artiste ; sa jouissance est aussi grande et de même nature.”
Henri Poincaré (1854–1912) first seen 1890 wikiquote, CC BY-SA 4.0 source
Recorded in: Notice sur Halphen," Journal de l'École Polytechnique (Paris, 1890), 60ème cahier, p. 143. See also Tobias Dantzig, Henri Poincaré, Critic of Crisis: Reflections on His Universe of Discourse (1954) p. 8
“C'est même des hypothèses simples qu'il faut le plus se défier, parce que ce sont celles qui ont le plus de chances de passer inaperçues.”
Henri Poincaré (1854–1912) first seen 1888 wikiquote, CC BY-SA 4.0 source
Recorded in: Thermodynamique: Leçons professées pendant le premier semestre 1888–1889 (1892), Preface
“La tâche de l'éducateur est de faire repasser l'esprit de l'enfant par où a passé celui de ses pères, en passant rapidement par certaines étapes mais en n'en supprimant aucune. À ce compte, l'histoire de la science doit être notre guide.”
Henri Poincaré (1854–1912) first seen 1899 wikiquote, CC BY-SA 4.0 source
Recorded in: La logique et l'intuition dans la science mathématique et dans l'enseignement" [Logic and intuition in the science of mathematics and in teaching], L'enseignement mathématique (1899)
“We do not have and cannot have any means of discovering whether or not we are carried along in a uniform motion of translation.”
Henri Poincaré (1854–1912) first seen 1904 wikiquote, CC BY-SA 4.0 source
Recorded in: L’état actuel et l’avenir de la physique mathematique (1904)
“Tout le monde y croit cependant, me disait un jour M. Lippmann, car les expérimentateurs s'imaginent que c'est un théorème de mathématiques, et les mathématiciens que c'est un fait expérimental.”
Henri Poincaré (1854–1912) first seen 1912 wikiquote, CC BY-SA 4.0 source
Recorded in: Calcul des probabilités (2nd ed., 1912), p. 171
“La pensée ne doit jamais se soumettre, ni à un dogme, ni à un parti, ni à une passion, ni à un intérêt, ni à une idée préconçue, ni à quoi que ce soit, si ce n'est aux faits eux-mêmes, parce que, pour elle, se soumettre, ce serait cesser d'être.”
Henri Poincaré (1854–1912) first seen 1909 wikiquote, CC BY-SA 4.0 source
Recorded in: Speech, University of Brussels (19 November 1909), during the festival for the 75th anniversary of the university's foundation; published in Œuvres de Henri Poincaré (1956), p. 152
“The ones who are preoccupied by logic are above all; to read their works, one is tempted to believe they have advanced only step by step, after the manner of a Vauban who pushes on his trenches against the place besieged, leaving nothing to chance. The others are guided by intuition and, at the first stroke, make quick but sometimes precarious conquests, like bold cavalrymen of the advance guard.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: quoted in Jacques Hadamard, An essay on the psychology of invention in the mathematical field (1954), pp. 106.
“Point set topology is a disease from which the human race will soon recover.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Quoted in D MacHale, Comic Sections (Dublin 1993)
“Talk with M. Hermite. He never evokes a concrete image, yet you soon perceive that the more abstract entities are to him like living creatures.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Quoted in G Simmons, Calculus Gems (New York 1992).
“Thought is only a flash between two long nights, but this flash is everything.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Quoted in H. L. Mencken, A New Dictionary of Quotations (Alfred A. Knopf, Inc., 1942)
“Douter de tout ou tout croire, ce sont deux solutions également commodes, qui l'une et l'autre nous dispensent de réfléchir.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Preface, Dover abridged edition (1952), p. xxii
“There is no science apart from the general. It may even be said that the very object of the exact sciences is to spare us these direct verifications.”
Henri Poincaré (1854–1912) first seen 1905 wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. I. (1905) Tr. George Bruce Halstead
“Les mathématiciens n'étudient pas des objets, mais des relations entre les objets ; il leur est donc indifférent de remplacer ces objets par d'autres, pourvu que les relations ne changent pas. La matière ne leur importe pas, la forme seule les intéresse.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. II: Dover abridged edition (1952), p. 20
“... les traités de mécanique ne distinguent pas bien nettement ce qui est expérience, ce qui est raisonnement mathématique, ce qui est convention, ce qui est hypothèse.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. VI: The Classical Mechanics, Tr. George Bruce Halsted (1913)
“Le savant doit ordonner ; on fait la science avec des faits comme une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. IX: Hypotheses in Physics, Tr. George Bruce Halsted (1913)
“It is often said that experiments should be made without preconceived ideas. That is impossible. Not only would it make every experiment fruitless, but even if we wished to do so, it could not be done. Every man has his own conception of the world, and this he cannot so easily lay aside. We must, for example, use language, and our language is necessarily steeped in preconceived ideas.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. IX: Hypotheses in Physics, Tr. George Bruce Halsted (1913)
“Si donc un phénomène comporte une explication mécanique complète, il en comportera une infinité d’autres qui rendront également bien compte de toutes les particularités révélées par l’expérience.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
Recorded in: Ch. XII: Optics and Electricity, as translated by George Bruce Halsted (1913)
“Scientists believe there is a hierarchy of facts and that among them may be made a judicious choice. They are right, since otherwise there would be no science...”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“One need only open the eyes to see that the conquests of industry which have enriched so many practical men would never have seen the light, if these practical men alone had existed and if they had not been preceded by unselfish devotees who died poor, who never thought of utility, and yet had a guide far other than caprice. As Mach says, these devotees have spared their successors the trouble of thinking.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Le temps et l’espace... Ce n’est pas la nature qui nous les impose, c’est nous qui les imposons à la nature parce que nous les trouvons commodes.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Il ne faut pas comparer la marche de la science aux transformations d’une ville, où les édifices vieillis sont impitoyablement jetés à bas pour faire place aux constructions nouvelles, mais à l’évolution continue des types zoologiques qui se développent sans cesse et finissent par devenir méconnaissables aux regards vulgaires, mais où un œil exercé retrouve toujours les traces du travail antérieur des siècles passés. Il ne faut donc pas croire que les théories démodées ont été stériles et vaines.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Cette harmonie que l’intelligence humaine croit découvrir dans la nature, existe-t-elle en dehors de cette intelligence ? Non, sans doute, une réalité complètement indépendante de l’esprit qui la conçoit, la voit ou la sent, c’est une impossibilité. Un monde si extérieur que cela, si même il existait, nous serait à jamais inaccessible. Un monde si extérieur que cela, si même il existait, nous serait à jamais inaccessible.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“What we call objective reality is, in the last analysis, what is common to many thinking beings, and could be common to all; this common part, we shall see, can only be the harmony expressed by mathematical laws. It is this harmony... which is the sole objective reality, the only truth we can attain; and when I add that the universal harmony of the world is the source of all beauty, it will be understood what price we should attach to the slow and difficult progress which little by little enables us to know it better.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“The mathematician is born, not made.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Pour qu’un ensemble de sensations soit devenu un souvenir susceptible d’être classé dans le temps, il faut qu’il ait cessé d’être actuel, que nous ayons perdu le sens de son infinie complexité, sans quoi il serait resté actuel. Il faut qu’il ait pour ainsi dire cristallisé autour d’un centre d’associations d’idées qui sera comme une sorte d’étiquette. Ce n’est que quand ils auront ainsi perdu toute vie que nous pourrons classer nos souvenirs dans le temps, comme un botaniste range dans son herbier les fleurs desséchées.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“But these labels can only be finite in number. On that score, psychologic time should be discontinuous.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[T]wo difficulties: (1) Can we transform psychologic time, which is qualitative, into a quantitative time? (2) Can we reduce to one and the same measure facts which transpire in different worlds [of conscious beings]!”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“We have not a direct intuition of the equality of two intervals of time.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[I]t is the sidereal day, that is, the duration of the rotation of the earth, which is the constant unit of time. ...However ...[many] astronomers ...think that the tides act as a check on our globe, and that the rotation of the earth is becoming slower and slower. Thus would be explained the apparent acceleration of the motion of the moon...”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[W]hat postulate do we implicitly admit? It is that the duration of two identical phenomena is the same; or... that the same causes take the same time to produce the same effects. ...Is it impossible that experiment may some day contradict our postulate?”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“In physical reality one cause does not produce a given effect, but a multitude of distinct causes contribute to produce it, without our having any means of discriminating the part of each of them. ...[C]auses which have produced a certain effect will never be reproduced except approximately.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[W]e should say: Causes almost identical take almost the same time to produce almost the same effects.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[A]stronomers... define duration in the following way: time... so defined that Newton's law and that of vis viva [or of the ] may be verified. Newton's law is an experimental truth... only approximate... [W]e still have only a definition by approximation.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“If... it be supposed that another way of measuring time is adopted... enunciation of the law would be... translated into another language... much less simple. So that the definition implicitly adopted by the astronomers may be summed up..: Time should be so defined that the equations of mechanics may be as simple as possible... [i.e.,] there is not one way of measuring time more true... only more convenient.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“We should like to represent... the... universe, and... feel... we understood it. We... never can attain this representation: our weakness is too great. But... we desire... to conceive an infinite intelligence... which should see all, and... classify all in its time, as we classify, in our time, the little we see. ...[T]his supreme intelligence would be only a ; infinite in one sense... limited in another, since it would have... imperfect recollection of the past... otherwise all recollections would be equally present... and for it there would be no time.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[Y]et when we speak of time... do we not unconsciously adopt this hypothesis... [and] put ourselves in the place of this imperfect god... [D]o not even the atheists put themselves in the place where god would be..?”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[This] shows, perhaps, why we have tried to put all physical phenomena into the same frame. But that can not pass for a definition of simultaneity, since this hypothetical intelligence, even if it existed, would be for us impenetrable. It is... necessary to seek something else.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Is not my present nearer my past of yesterday than the present of Sirius?”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Behold... the only... [rule] we can follow: when a phenomenon appears... as the cause of another, we regard it as anterior. ...[T]herefore by cause... we define time; but...how do we recognize which is the cause and which the effect? We assume... the anterior fact, the antecedent, is the cause of the... consequent. It is then by time that we define cause. ...[S]hall we escape from this vicious circle?”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“[H]ave we really the right to speak of the cause of a phenomenon?”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Si toutes les parties de l’univers sont solidaires dans une certaine mesure, un phénomène quelconque ne sera pas l’effet d’une cause unique, mais la résultante de causes infiniment nombreuses ; il est, dit-on souvent, la conséquence de l’état de l’univers un instant auparavant.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“When an astronomer tells me that some stellar phenomenon, which his telescope reveals to him at this moment, happened... fifty years ago... I... ask... how he has measured the velocity of light.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“He has begun by supposing that light has a constant velocity... the same in all directions. This... could never be verified directly by experiment... The postulate... resembling the ... furnishes us with a new rule for the investigation of simultaneity.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Roemer used eclipses of the satellites of Jupiter, and sought how much the event fell behind its prediction. But... this prediction [is] made... by... astronomic laws; for instance Newton's... [T]he velocity of light... is adopted, such that the astronomic laws compatible with this value may be as simple as possible.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“When navigators... determine a ... they must... calculate Paris time...[with] a chronometer set for Paris. The qualitative problem of simultaneity is made to depend upon the quantitative problem of the measurement of time.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Or... they observe an astronomic phenomenon... an eclipse of the moon, and... suppose... this... is perceived simultaneously from all points of the earth. That is not altogether true, since the propagation of light is not instantaneous; if absolute exactitude were desired, there would be a correction... according to a complicated rule.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“(1) The rules applied are exceedingly various. (2) It is difficult to separate the qualitative problem of simultaneity from the quantitative problem of the measurement of time; no matter whether a chronometer is used, or whether account must be taken of a velocity of transmission, as... of light, because such a velocity could not be measured without measuring a time.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“Comme nous ne pouvons pas donner de l'énergie une définition générale, le principe de la conservation de l'énergie signifie simplement qu'il y a quelque chose qui demeure constant.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“What is objective must be common to many minds and consequently transmissible from one to the other, and as this transmission can only come about by... discourse... we are even forced to conclude: no discourse no objectivity.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source
“It is only through science and art that civilization is of value. Some have wondered at the formula: science for its own sake; an yet it is as good as life for its own sake, if life is only misery; and even as happiness for its own sake, if we do not believe that all pleasures are of the same quality... Every act should have an aim. We must suffer, we must work, we must pay for our place at the game, but this is for seeing's sake; or at the very least that others may one day see.”
Henri Poincaré (1854–1912) said by 1912 at the latest wikiquote, CC BY-SA 4.0 source