This paper advances the core thesis that the speed of light is the limit of physical quantities, not the limit of spacetime quantities. The "superluminal" correlations of quantum entanglement and the "superluminal" recession of distant galaxies in cosmic expansion are not violations of relativity, but rather because these two phenomena belong to the category of spacetime quantities and fall outside the jurisdiction of the speed of light. Through the methodology of "hierarchical reclassification," this paper separates physical quantities (matter, energy, signals, causal chains) from spacetime quantities (spacetime structure, expansion, connectivity, topological relations), pointing out that the definition of velocity (m/s) presupposes "matter moving through space"; when the object of discussion is spacetime itself, the concept of "velocity" no longer applies. This paper further clarifies that there is no fundamental contradiction between relativity and quantum mechanics requiring "unification"—they describe effective laws at different levels (the L4 physical level and the L1–L2 quantum level). The "superluminal paradox" that has long troubled physics is, in essence, a result of category misplacement.
Higgs Boson Spookiness: Probing Quantum Nonlocality with Spacetime-Resolved H→τ+τ− Decays
We demonstrate that a future precision ee Higgs factory would be able to perform a spacetime-resolved test of quantum nonlocality in Higgs boson decays. In simulated ee→ZH→(μμ)(ττ) events at s=240 GeV, we reconstruct τ lepton decay vertices and measure spin correlations as a function of the spacetime interval between the two τ decays. Such a measurement would be able to test Bell-inequality-violating correlations for spacelike-separated decays, enabling direct exclusion of superluminal, finite-speed entanglement signaling theories. With 0.75 ab−1 of integrated luminosity, entanglement signal propagation speeds below ≈2c can be excluded at 95% CL. Signals establishing any spin correlation can be excluded for speeds below ≈9c. This constitutes the first proposed spacetime-resolved measurement of electroweak quantum entanglement at a particle collider and demonstrates a unique capability of future Higgs factories.
For Klein?Gordon and Dirac waves representing massive quantum particles, the local group velocity v (weak value of the velocity operator) can exceed c. If the waves consist of superpositions of many plane waves, with different (but subluminal) group velocities u, the superluminal probability Psuper, i.e. that |v| > c for a randomly selected state, can be calculated explicitly. Psuper?depends on two parameters describing the distribution (power spectrum) of u in the superpositions, and lies between 0 and 1/2 for Klein?Gordon waves and 1?1/ and 1/2 for Dirac waves. Numerical simulations display the superluminal intervals in space and regions in spacetime, and support the theoretical predictions for Psuper.