Information Causality¶
A proposed principle limiting Bob's information gain about Alice's unknown data to the n classical bits she sends, even with pre-shared nonsignalling correlations.
Core Idea¶
Information causality is a proposed bound on a communication-assisted information task. Alice may share a nonsignalling resource with Bob, but if she sends only n classical bits, Bob's total gain about data previously unknown to him cannot exceed that n-bit budget under the principle's definition.
This is stronger than no-signalling alone and is useful for testing hypothetical post-quantum correlations. The claim is not a general law that all information must have a physical sender; it is a particular classical-message task, and its bipartite success does not settle every multipartite case.
Scope of Application¶
This is a proposed physical principle for limited classical-message tasks with possible pre-shared correlations.
- Quantum foundations. Screens candidate correlation theories by a constraint beyond no-signalling alone.
- Communication tasks. Compares Alice's classical message budget with Bob's total new information about hidden data.
- Bell-correlation analysis. Excludes certain post-quantum nonsignalling resources that would overrun the information budget.
- Multipartite research. Marks the limits of extending a bipartite principle to every quantum correlation scenario.
Clarity¶
Fix Alice's initially unknown data, Bob's prior knowledge, their pre-shared resource, the classical message length, and the task's information-gain measure. The principle compares Bob's total new gain with that message budget; no-signalling alone is weaker. Do not apply this particular bound unchanged to transmitted qubits or treat bipartite success as a full multipartite characterization. A one-bit message is the permitted communication; entanglement is a pre-shared resource, not an extra classical bit sent afterward.
Manages Complexity¶
Prior knowledge, local computation, shared correlations, and sent messages can all affect a retrieval task. Information causality organizes them around one comparison: Bob's new information about Alice's initially unknown data versus the classical bits Alice actually sends. The comparison is meaningful only with its task and gain measure fixed; a slogan about information having causes is too broad.
Abstract Reasoning¶
Formulate the Alice–Bob retrieval task and permitted pre-shared correlation, then calculate or bound Bob's gain after the n-bit classical message. Compare it with n and identify the correlation regime in which the result holds. A result for one bipartite task cannot settle all multipartite quantum boundaries. This separates an operational violation from mere existence of nonlocal correlation.
Knowledge Transfer¶
The message-budget test transfers among bipartite information-causality games that retain the same classical channel and information-gain definition. Its cargo is a bound on total newly accessible information despite pre-shared correlations, not a ban on correlations themselves. No-signalling is a related but weaker restriction. Quantum-message tasks, ordinary causal inference, and unrestricted multipartite settings require different assumptions, so the named principle cannot be carried there unchanged or claimed to characterize all quantum theory.
Neighborhood in Abstraction Space¶
Information Causality sits in a moderately populated region (41st percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.
Family — Quantum States & Computational Models (12 abstractions)
Nearest neighbors
- Entanglement Distillation — 0.91
- Quantum Computing — 0.88
- Network Transparency — 0.87
- Higher-Order Message — 0.87
- Channel State Information — 0.87
Computed from structural-signature embeddings · 2026-10-08