{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"89425fa9444ccc026e2d1cbfc1d96307715ab97d39f0e66e35863682a9880556","created":"2026-10-03T07:18:10Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"16bc8a3faecf03abffd2e959c3bdab50575dfc07214d108d1d1ae0829e95950a","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"qi.measurement-problem.definite-outcomes","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"When a detector interacts with a particle in a superposition (a blend of states), the Schrodinger equation predicts a blended detector, yet one reading is always seen. The question is what physical process or rule selects that single reading.","posed_since":"","precise":"For a system $S$ in state sum_k c_k |k> coupled unitarily to apparatus $A$ and environment $E$, unitary evolution gives sum_k c_k |k>|A_k>|E_k>; decoherence makes the reduced density matrix of $S+A$ diagonal but selects no single $k$. Required: a modified dynamics, an added ontology (hidden variables, branches) or a principled account that yields single outcomes with frequencies $\\mid c_k\\mid^2$, together with either predictions that differ from standard quantum mechanics or a proof of empirical equivalence. This is the root problem of the topic; its workable sharper forms are listed under related.","problem_ref":null,"references":"","settled_by":"An experiment detecting a deviation from unitary evolution predicted by one class of proposals, or a proof that a specified account reproduces all quantum predictions using only its stated assumptions.","status_note":"","title":"Why does a measurement produce one definite outcome?","topic_ref":"53eaac23eff60d38a9fc30e8fae69f8801e09051272e1b1d322d1c034216f53b"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"aae6a1ff99d44ce28f57912944d7e9b374bca3e3373a1f42ec8e05762624121a","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"2522820a3285b7389e3e7295b4b4acbded4f9deb9f18fda2902532a7a8ff8bcf","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"AF08KzaIPgpeaBhYzER6rnK5o0ByslnKWa5HD5ufCk-Yk8SpdWFQzDoA_7FX6Bq_rQKQD276F32mjs0c10IeCg"},"schema":"pubphys.envelope/1"},"record_hash":"aae6a1ff99d44ce28f57912944d7e9b374bca3e3373a1f42ec8e05762624121a","leaf_index":2014}