{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"074331ff6289baebfcc7ecaf74d439e7e495b728fa7d9a52534afbb2254b23cd","created":"2026-10-03T07:18:10Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","c1f790f8de35d3d5f60c9a6639d7ec2e82b87f301b7e81cc6890231b220c7bef"],"salt":"4f739275865974c9c637b307ae20c9cda75409ca2795c54004775325241bd70c","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":"1","parents":[{"note":"","parent_revision":"c1f790f8de35d3d5f60c9a6639d7ec2e82b87f301b7e81cc6890231b220c7bef","relation":"special_case"}],"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 $m \\sim 1e-11\\,\\mathrm{g}$, each in a spatial superposition of size $\\Delta x \\sim 2.5e-2\\,\\mathrm{cm}$ at separation $d \\sim 4.5e-2\\,\\mathrm{cm}$, 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":null,"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 $1e-11\\,\\mathrm{g}$ has been made; 2026 analyses give witness values of order $-1e-2$ for $m = 1e-11\\,\\mathrm{g}$ 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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