Does quantum matter warp the rules of causality itself?

Two physicists show that when matter exists in quantum superposition, it creates an operator-valued Shapiro delay that quantizes the light cones themselves. This means the causal structure of spacetime gains irreducible quantum uncertainty: two events can exist in superposition between timelike and spacelike separation, and tracing out the quantum source produces an effective ultraviolet cutoff in the Wightman singularity.