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Everettian branching diagram with three diverging paths and relativistic events — Everettian branching and relativistic events

The Problem

The central problem is how to describe measurement outcomes when quantum theory permits different observers to assign different state updates, while relativistic descriptions do not supply a universal ordering of spacelike-separated events. A satisfactory Everettian account would need to explain how branching and observer records fit that setting without turning quantum correlations into controllable superluminal signals; the packet identifies these pressures but does not provide the full account. [S2, S4, S9]

Supports The measurement problem concerns the apparent tension between unitary state evolution and the definite outcomes associated with measurement. [S3]

Constrains Relativistic discussions of measurement must distinguish conditional state assignments after a specified outcome from non-selective local operations, which leave remote marginal statistics unchanged. [S4]

Extends Everettian accounts also face a question about how to understand observers’ uncertainty around branching, although the packet presents this connection as philosophically controversial. [S9]

Evidence · 4 works

Rival Explanations

The packet documents alternatives to Everettian branching, but does not compare them systematically as solutions to the specific relativistic-branching problem. Relational event accounts make events relative to systems or contexts; other proposals retain a single spacetime history or introduce a measurement-localizing mechanism. Their presence shows that the reconciliation question is interpretation-dependent, not that any alternative has been established as superior. [S1, S2, S5, S10, S19]

Contested Relational event approaches treat events as relative to systems or observational contexts, with causal structure helping identify events; the packet does not show that this framework is an Everettian account. [S1, S10]

Challenges A single-history proposal treats quantum states as incomplete information about possible spacetime histories and takes one history to represent underlying reality, rather than positing Everettian branches. [S5]

Challenges A proper-time proposal seeks to address simultaneity concerns by redefining the wavefunction’s time parameter, but it also introduces deterministic measurement localization and therefore does not preserve Everettian branching as described in the packet. [S19]

Challenges One proposed alternative to radical non-absoluteness keeps observed events absolute while relativizing interaction states, and its author notes that a special form of retrocausality might be needed. [S2]

Evidence · 5 works

What Remains Unresolved

The central open task is to supply a concrete relativistic Everettian model: it would need to define branching and records without relying on an unexplained preferred ordering of spacelike events, and show how observers’ accounts fit together. The packet also leaves open whether the relevant non-absoluteness results impose an ontological lesson or only a constraint on descriptions and predictions. [S2, S4, S9, S17]

Unresolved The packet does not specify how branches are individuated or related between spacelike-separated measurements in a relativistic theory. [S4, S9]

Unresolved It remains unclear from these sources whether non-absoluteness results require observer-relative events, allow multiple outcomes per observer, or can be handled through another interpretation of their assumptions. [S2, S17]

Evidence · 4 works

Supporting evidence

The packet does not specify how branches are individuated or related between spacelike-separated measurements in a relativistic theory. [S4, S9]

Local measurement in entangled systems: Conditional states, quantum instruments, and the no-signalling theorem

Sachin · 2025 · International Journal of Physics and Mathematics

Why it matters: It supplies the clearest operational relativistic constraint: conditional state updates do not enable controllable superluminal signalling.

On Time chez Dummett

Jeremy Butterfield · 2014 · arXiv (Cornell University)

Why it matters: It links Everettian splitting and observer uncertainty to questions about time, while identifying the connection as controversial.

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