It is said that Poincaré, when finally convinced that the evidence of atoms was overwhelming, exclaimed something like "but then it's all false!", meaning that

It is said that Poincaré, when finally convinced that the evidence of atoms was overwhelming, exclaimed something like "but then it's all false!", meaning that all the continuum-based theories like fluid dynamics and electrodynamics, which had previously seemed like exact descriptions of the underlying reality, had suddenly shown themselves to be mere approximations...