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Title: Close the decoherence-diffusion window for classical gravity
Plain: If gravity is classical while matter is quantum, consistency requires gravity to both blur superpositions and make the gravitational pull jitter randomly. Measuring both effects together can exclude such theories.
Precise: In classical-quantum gravity (Oppenheim and coworkers), the decoherence coefficient $D_2$ for mass superpositions and the diffusion coefficient $D_0$ of the Newtonian potential obey a trade-off with $D_0D_2$ bounded below (Oppenheim, Sparaciari, Soda, Weller-Davies, Nature Communications 2023). Determine whether coherence times from matter-wave interferometry combined with acceleration-noise data (torsion balances, Cavendish-type experiments, LISA Pathfinder) exclude the entire allowed $(D_0,D_2)$ region for each choice of kernel.
Settled by: Joint bounds from interferometric coherence and gravitational acceleration noise leaving no allowed $(D_{0}, D_{2})$ for the model class.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: The trade-off was derived in 2022-2023 (arXiv:2203.01982); 2025 proposals test it via classical diffusion of probe masses (arXiv:2501.13030).
Posed since: 2022