{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"354003ac39616843c83e600f709547067b385069f398d32537c93135e03f8a1b","created":"2026-10-03T07:17:53Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"8c7191331ce26c9b55d2deed8871801f98f2ea3ff355cf194ba5016f454e52d9","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.casimir-dispersion-forces.quantum-friction","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"Two smooth surfaces sliding past each other without touching might still feel a drag from quantum fluctuations of the field between them, even at zero temperature. Most theories predict a tiny nonzero drag, but they disagree on how it depends on speed and distance, and no experiment has detected it.","posed_since":"","precise":"Two planar half-spaces with dielectric response $\\varepsilon(\\omega)$ at gap $d$, moving parallel with constant velocity $v << c$, at $T = 0$ and in vacuum. Quantity: the lateral force $F_x(v, d)$ and its exponents at small $v$ (for Drude metals treatments give $F_x \\sim v^{3} / d^{n}$, with $n$ and prefactors differing between formalisms, and some model treatments find zero). An answer is the $T = 0$ exponents and prefactor of $F_x(v, d)$ agreed across macroscopic-QED formalisms for dissipative media, plus a measurement of a velocity-dependent drag separated from thermal and electrostatic contributions.","problem_ref":null,"references":"","settled_by":"A derivation of $F_{x}(v, d)$ at $T = 0$ accepted across competing formalisms, and a measurement with an atom, nanoparticle or tip moving near a surface that isolates the quantum term.","status_note":"No observation exists; the zero-temperature result was disputed by Philbin and Leonhardt (2009) and answered by Pendry (2010), and the scaling still differs between treatments.","title":"Speed and distance dependence of non-contact quantum 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