Physicists believe that the Gaussian law has been proved in mathematics while mathematicians think that it was experimentally established in physics. - Henri Poincaré

None of our sensations, isolated, could have conducted us to the idea of space; we are led to it only in studying the laws, according to which these sensations succeed each other.

The readings we shall be able to make on our instruments at any instant will depend only on the readings we could have made on these same instruments at the initial instant.

The object of mathematical theories is not to reveal to us the real nature of things; that would be unreasonable claim. Their only object is to coordinate the physical laws with which physical experiments make us acquainted, the enunciation of which, without the aim of mathematics, would be unable to effect.