Quantum Time & History

Preface

Does time really flow, or is it an illusion?

In everyday experience, time undeniably seems to pass, yet quantum cosmology hints at a “frozen universe” without an external ticking clock. This book “Quantum Time & History” follows the trail of how the notions of time and history can emerge from a fundamentally quantum substrate.

The journey begins with Hilbert spaces and path integrals, then confronts one of quantum theory’s deepest puzzles: the emergence of classicality from quantum possibilities. Through consistent histories and quantum Darwinism, it explores how a single objective classical world is selected from infinitely many quantum branches.

Finally, it challenges the very nature of time and reality. Is time a relational phenomenon arising from entanglement (Page–Wootters), or an intrinsic property encoded in the state itself (thermal time)? Did history exist even when no one was looking (Leggett–Garg inequalities)?

This is not a standard textbook, but a record of an inquiry that tries to reconstruct the meaning of the “present,” the essence of the “past,” and the structure of “reality” at the quantum level.