The Superposition Principle in Macroscopic Systems

Jesús Unturbe, J. L. Sánchez‐Gómez

Nancy Delaney Cartwright

Lisa Doumbouya

Quantum mechanics provides an extraordinarily accurate description of microscopic systems, yet persistent conceptual difficulties arise when its superposition principle is naively extended to systems involving significant mass displacement. In particular, macroscopic superpositions imply the coexistence of distinct gravitational field configurations, raising questions of spacetime consistency rather than measurement or environmental interaction. This short note argues that the apparent breakdown of macroscopic superposition does not require a collapse mechanism or modification of quantum dynamics. Instead, it reflects a structural admissibility constraint: spacetime permits only one future-consistent geometry sourced by mass. From this perspective, the absence of macroscopic superpositions is a consequence of structural selection rather than dynamical collapse, reframing long-standing debates surrounding quantum mechanics and gravity.

Nancy Delaney Cartwright

Byoung Seung HAM

Quantum entanglement is the quintessence of quantum information processing mostly limited to the microscopic regime governed by Heisenberg uncertainty principle. For practical applications, however, macroscopic entanglement gives great benefits in both photon loss and sensitivity. Recently, a novel method of macroscopic entanglement generation has been proposed and demonstrated in a coupled interferometric system using classical laser light, where superposition between binary bases in each interferometric system plays a key role. Here, the function of path superposition applied to independent bipartite classical systems is analyzed to unveil secrets of quantum features and to convert a classical system into a quantum system without violating quantum mechanics.

Matts Roos