The Universe in four letters: a bedtime history

Abstract

One evening, a father tells his three daughters, Lucía, Inés, and Ana, a bedtime story unlike any other. It is a tale of four silent architects ($c$, $\hbar$, $G$, and $Λ$) whose presence or absence shapes the very fabric of reality. By imagining worlds where each constant is removed, they explore realms from the quantum gravity of the Planck scale to the stretching cosmos of de Sitter space, from the mass of the observable Universe to the surprising link with the proton's whisper. Woven with the insights of great scientists, this narrative reveals how these fundamental constants write the story of everything, from the smallest particle to the vast cosmic horizon, suggesting a beautiful and hidden unity in the architecture of our world.