Henri Poincaré was a famous mathematician, theoretical physicist, and philosopher.

"Think of two consciousnesses, which are like two worlds impenetrable one to the other. By what right do we strive to put them into the same mold, to measure them by the same standard? Is it not as if one strove to measure length with a gram or weight with a meter? And besides, why do we speak of measuring? We know perhaps that some fact is anterior to some other, but not by how much it is anterior.

Therefore two 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?..."