Prologue: The Zeroth Law of RealityA Hidden Line of Order Guiding InsightPhysics appears diverse, yet its patterns of change follow a singlelogic. To see it is not to invent new laws, but to notice a structure thatwas always present.Instantaneity never appears in nature.Every system takes time to update itself. Heat requires duration tospread. Light requires duration to travel. A particle requires duration torespond. A black hole requires duration to ring down.This quiet fact—so obvious that it escapes attention—will guide theentire book.We will read physical theories through one axis: the causal memoryscale, τc.This parameter measures how long a system must “settle itself” beforeit can update its state. It is not a correction. It is not a technicality. Itis the structural parameter that unifies heat conduction, quantum mass,and gravitational ringdown into a single line of order.The present is never instantaneous.It is always a window—however brief—through which the pastshapes what comes next.When we restore this window to our equations, physics simplifies.Disconnected phenomena align. Apparent paradoxes dissolve. A quietunification appears.This book is an invitation to see that structure.—Y.L., Bangkok, 2025