Who said: The shortest trajectory between two realities is complex?

Question

Who said: The shortest trajectory between two realities is complex?

I'm not sure of the citation, but the idea is that even when working on "real" problems the best way is to pass through "complex" problems (e.g. using residue theorem to compute complicated real integrals).

Answer 1

It seems to be the French mathematician Jacques Hadamard:

Le plus court chemin entre deux vérités dans le domaine réel passe par le domaine complexe.

It was translated into English by J. P. Kahane (who passed away recently):

The shortest path between two truths in the real domain passes through the complex domain.

For other details, you can look at this page.