The Proton Radius Puzzle —— The Inevitability of Measurement Tool Self-Reference

Since its discovery in 2010, the proton radius puzzle has troubled the physics community for sixteen years. Electron measurements gave approximately 0.877 fm, while muon measurements gave approximately 0.841 fm—a 4% discrepancy inexplicable within the standard model. In April 2026, two independent experiments finally confirmed the muon result, concluding that early electron measurements suffered from systematic errors. Mainstream physics considers the puzzle solved. From the perspective of World Quantum Theory’s projection layer epistemology, this paper reveals a deeper fact: the 4% discrepancy is not an error but the inevitable manifestation of phase-locking deviation between different probes operating on the same projection layer at different frequency windows. Even when current experiments “calibrate” electron measurements to match the muon result, this remains merely a recalibration within a self-referential system and does not dissolve the fundamental structure of “measurement tool self-reference.” This paper demonstrates that the proton radius puzzle is not a technical problem but an instance of the principle that “the measuring instrument is always part of the world being measured.” Keywords: Proton Radius Puzzle; World Quantum Theory; Projection Layer; Phase-Locking; Self-Referential Measurement