{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"4c3bdbf1c6b46bd4cc55fc49f17a7c253110cd3cfc16c376de48f517ad42d341","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["53e6ac3ec36021d7ef338000aeb5a16a80a0727f6973ad5e69fb0a3e6e017ef4","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"bf47b134b7b30bab4f92814eefda4836e06e83e918749d275deed597743ae727","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"qi.gravity-quantum.gme-observation","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Two tiny crystals, each in a superposition of two places, are let fall side by side; if gravity is quantum, their attraction should entangle them within seconds. This needs masses of roughly a hundred-billionth of a gram kept coherent for seconds with almost no other force between them.","posed_since":"2017","precise":"Two masses $m \\sim 10^{-11}\\,\\mathrm{g}$, each in a spatial superposition of size $\\Delta x \\sim 2.5 \\times 10^{-2}\\,\\mathrm{cm}$ at separation $d \\sim 4.5 \\times 10^{-2}\\,\\mathrm{cm}$, acquire branch-dependent phases $\\phi = G m^{2} t / (\\hbar d)$ over $t \\sim 2.5\\,\\mathrm{s}$ (illustrative parameters of Bose et al. 2017, approximate). Demonstrate a positive entanglement witness (e.g. embedded-spin correlations) with Casimir-Polder and electromagnetic couplings suppressed below the gravitational one and decoherence rates below $1/t$.","problem_ref":"53e6ac3ec36021d7ef338000aeb5a16a80a0727f6973ad5e69fb0a3e6e017ef4","references":"","settled_by":"A positive entanglement witness between two masses whose only significant interaction is gravity.","status_note":"As of 2026 no spatial superposition of a mass near $10^{-11}\\,\\mathrm{g}$ has been made; 2026 analyses give witness values of order $-10^{-2}$ for $m = 10^{-11}\\,\\mathrm{g}$ over 0.1 s with decoherence rates of $0.1 \\text{ to } 1\\,\\mathrm{s}^{-1}$ (arXiv:2609.10697).","title":"Observe entanglement created only by gravity between two 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