Experiment is the sole source of truth. It alone can teach us something new; it alone can give us certainty. - Henri Poincaré

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.

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.

[W]e should say: 'Causes almost identical take almost the same time to produce almost the same effects.'