1 min read
| Status | Active — read in full 2026-10-27 (NOTE-1214), from arXiv v2; worth reading as the quantitative restatement of relational quantum mechanics, with relative facts defined by relative information and held by commutative subalgebras rather than by quantum systems. The definitions are clean. The resolutions it claims (combination problem, Frauchiger–Renner, intersubjectivity) are paragraphs or citations, and every consistency check is computed relative to one outside system. |
| Version | 2 |
| Tags | quantum-foundations, information-theory |
| Cited as “paper” by | NOTE-1214 — Di Biagio & Rovelli — Relative information, relative facts |
| Cited as “source” by | THEORY-1069 — In a von Neumann measurement the measuring variable's information about the measured variable grows continuously under the unitary coupling, in Di Biagio and Rovelli's model as I_{A:B}(t) = sin²(ωt)H_A, so the discontinuity of a quantum measurement lies only in a threshold on when information counts as a fact; with an idealized pure ready state a fact conditional on a pointer value appears at once, which they attribute to the idealization, THEORY-1074 — In Di Biagio and Rovelli's relational account two classical subsystems' perspectives merge, agreeing on a variable's value and on each other's, when they couple to that variable or to each other, and a coupling to a complementary variable can remove a relative fact from a perspective that did not interact; that this answers the combination problem and keeps perspectives consistent is shown only in worked examples computed relative to a single outside system, THEORY-1093 — In Di Biagio and Rovelli's reformulation of relational quantum mechanics a relative fact is a conditional probability concentrated on one value: A is a fact relative to B when the relative information I_{A|B} = I_A + I_{A:B} is maximal; since only commuting variables have a joint distribution, perspectives belong to commutative subalgebras of observables, not to quantum systems, so a qubit has none, and the joint distribution is itself relative to a further system, so the relativity iterates, THEORY-1213 — In relational quantum mechanics as Di Biagio and Rovelli reformulate it, classical subsystems whose variables couple properly, so as to get correlated, come to agree, so that the merging of perspectives answers the combination problem and the facts held relative to different outside systems never conflict about the same variables |
Di Biagio, A., & Rovelli, C. (2025). Relative information, relative facts. arXiv:2510.11349.
Read in full on 2026-10-27 (NOTE-1214).
A19 §3 called it “high-priority new prior art” for a generic notion of measurement. It bears on QUESTION-285. The reading found it exact for the question’s lowest rungs, correlation and complete correlation between commuting variables, and silent on records, use and revision (NOTE-1214).