Perturbation

Definition and stakes

Portrait of Marcus Tullius Cicero Marcus Tullius Cicero,  Cicero's Tusculan Disputations

“ For as every disorder or perturbation is a motion of the mind, either devoid of reason, or in despite of reason, or in disobedience to reason, and as that motion is excited by an opinion of either good or evil; these four perturbations are divided equally into two parts: for two of them proceed from an opinion of good, one of which is an exulting pleasure, that is to say, a joy elated beyond measure, arising from an opinion of some present great good ”
Source: Gutenberg

Portrait of Henri Poincaré Henri Poincaré,  The Foundations of Science (1913)

“ If the energy propagates itself indefinitely without encountering a receiver, the compensation will never occur.
Shall we say that the space which separates the oscillator from the receiver and which the perturbation must pass over in going from the one to the other is not void, that it is full not only of ether, but of air, or even in the interplanetary spaces of some fluid subtile but still ponderable; that this matter undergoes the shock like the receiver at the moment when the energy reaches it, and recoils in its turn when the perturbation quits it!
”
Source: Wikisource

Portrait of Zhuang Zi Zhuang Zi,  Chuang Tzŭ (1889)

“ For whether when the mind is locked in sleep or whether when in waking hours the body is released, we are subject to daily mental perturbations,—indecision, want of penetration, concealment, fretting fear, and trembling terror. ”
Source: Wikisource

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