The Particle That Exists in Spacetime: A 4D View of the Double-Slit Experiment

This article presents a conceptual interpretation of the double-slit experiment using Feynman's path integral formulation. Rather than treating a quantum particle as a point-like object following a single trajectory, the particle's propagation is viewed as a distributed structure in 4D spacetime. In the path-integral picture, this structure is represented by a coherent sum over possible paths between emission and detection. From this perspective, the observed interference pattern emerges from the phase relationships between these possible spacetime paths. The article distinguishes between propagation and interaction. Propagation is described as an extended 4D process, while measurement appears as a localized spacetime event within a 3D spatial slice, producing the point-like detections observed in the double-slit experiment. The aim is not to propose a new physical theory or to explain the mechanism of collapse, but to provide an intuitive geometric interpretation of the standard quantum formalism and its relationship between quantum propagation, interference, and localized measurement outcomes. This is a conceptual essay and interpretive synthesis, not a proposal of a new physical theory.