Common-Knowledge Broadcast¶
Coordination artifact — instantiates Coordination Equilibrium Shift
A single credibly-sourced notice delivered to every relevant actor at once, so the selected option becomes not just known but known to be known by all.
Even after a convention is chosen, coordination can still fail because each actor privately knows the target yet cannot safely assume the others do. Common-Knowledge Broadcast attacks precisely that gap. It is the public statement, ledger, or synchronized notice — issued once, from a source everyone recognizes, over a channel everyone can see is public — whose job is to lift a fact from privately known to common knowledge: everyone knows it, everyone knows that everyone knows it, and so on. Its distinctive contribution is the higher-order layer. It does not decide the option and it does not track who has actually moved; it engineers the shared certainty that lets each actor act as if the others will, because now they can see that the others have the same information they do.
Example¶
A city moves household recycling from weekly mixed collection to a fortnightly two-stream schedule. Most residents would happily comply, but each hesitates: put the wrong bin out on the wrong week and it sits uncollected, so people wait to see what neighbors do, and the old pattern persists. The public-works department issues a single broadcast — an identical dated card to every address, the same notice in the one local paper everyone reads, and matching signage — all keyed to one effective date and carrying a phone line to confirm or correct. Because the notice is visibly public and identical for all, each resident can infer that their neighbors received the same thing and know that they did too. That mutual visibility, not the persuasiveness of the recycling argument, is what makes the whole street set out the correct bin on the first new collection day.
How it works¶
The mechanism is a publication engineered for common knowledge, which distinguishes it from an ordinary announcement. It uses a single canonical source with recognized standing, so there is no ambiguity about which message is authentic. It delivers an identical payload to the entire bounded audience as close to simultaneously as possible, over a channel whose publicness each actor can observe — that observability is what generates the "everyone knows that everyone knows" layer. And it carries an authentication and correction path so counterfeit or conflicting versions can be defeated before they fragment expectations. It fires at defined synchronization points rather than continuously; sustaining a live tally of who has complied is a different mechanism's job.
Tuning parameters¶
- Audience boundary — how completely the broadcast reaches every relevant actor. A pocket that never got the notice, or doesn't know others did, is where coordination frays.
- Channel publicness — private per-actor notices versus a visibly shared channel. Publicness is what manufactures higher-order knowledge, but it trades against privacy.
- Source authority — whose name the notice carries. More recognized authority is more readily believed, at the cost of concentrating trust in one issuer.
- Synchronization tightness — one instantaneous drop versus a staggered rollout; tighter timing yields stronger common knowledge but is harder to execute.
- Correction latency — how quickly conflicting or false versions are identified and countered.
When it helps, and when it misleads¶
It is powerful when the residual block is purely epistemic — the target is chosen and privately preferred, and all that remains is for everyone to know that everyone knows.[n1] In that case a single well-made notice can do what months of one-to-one persuasion cannot. It misleads when it is used to manufacture false common knowledge: broadcasting "everyone is switching" before it is true, to stampede adoption. That can work briefly and then collapses hard when reality diverges from the announcement, and it burns the issuer's credibility for next time. It is also the wrong tool when the block is real payoff conflict or early-mover risk — louder shared knowledge does nothing for an actor who would lose by moving. The discipline is to broadcast only what is verifiable, keep the correction channel open, and hand genuine risk to the assurance and bridge mechanisms.
How it implements the components¶
coordination_dilemma_and_actor_boundary— the broadcast defines and must reach the full bounded set of relevant actors; the audience it addresses is the actor set among whom knowledge has to be common.beliefs_expectations_and_common_knowledge_map— its whole output is a shift in that map, converting fragmented first- and higher-order beliefs into shared common knowledge of the selected option.
It does not choose the option or certify its legitimacy — that is Focal Standard and Effective Date — and it does not maintain the live, verified view of who has actually committed or become ready, which is Commitment and Readiness Dashboard.
Related¶
- Instantiates: Coordination Equilibrium Shift — it establishes the shared knowledge on which the selected equilibrium depends.
- Consumes: Focal Standard and Effective Date supplies the selected option and effective moment that the broadcast propagates.
- Sibling mechanisms: Commitment and Readiness Dashboard · Focal Standard and Effective Date · Anchor-Participant Pact · Conditional Assurance Contract · Coordinated Migration Window · Default Switch with Protected Opt-Out · Bridge Subsidy and First-Loss Guarantee · Pilot Cohort and Cascade · Equilibrium Review and Reselection Trigger
Editorial Notes¶
Form Classification¶
Form family: Communication, Facilitation & Learning
Rationale: A single credibly-sourced notice delivered to every relevant actor at once, so the selected option becomes not just known but known to be known by all, making its operative form a designed message, facilitated interaction, ritual, or learning activity that changes shared understanding.
Independent corroboration: The frozen evidence defines Common-Knowledge Broadcast as 'A single credibly-sourced notice delivered to every relevant actor at once, so the selected option becomes not just known but known to be known by all', so its operative form is Communication, Facilitation & Learning.
Review outcome: Independent reviewer agreement; high confidence.
Origin Attribution¶
Primary origin: Economics & Finance
Origin pattern: Cross-disciplinary synthesis
Present-day reach: Multi-domain
Rationale: Coordination-game theory formalized public, mutually observed announcements as generators of common knowledge.
Related originating lineages:
- Communication & Media Studies — Broadcast practice contributes simultaneous delivery, source credibility, authentication, and correction across a bounded audience.
Review resolution: Both reviewers agree on economics_finance as primary. Reading the source mechanism confirms that its defining operation belongs to that lineage; the final record retains communication_media_studies only where it materially formed the mechanism and keeps present-day application breadth separate from provenance.
Encyclopedia synthesis: The exact catalogued form synthesizes established practice rather than reproducing a single standard historical label.
Review outcome: Reconciled after independent review; high confidence.
Notes¶
The broadcast is a one-shot common-knowledge act at synchronization points; the Commitment and Readiness Dashboard is its continuous counterpart, maintaining a live shared view as commitments and readiness evolve. They are easily conflated but do different work: the broadcast makes the selection commonly known; the dashboard keeps the changing participation state commonly known. A shift that needs both a clean starting cue and ongoing visibility uses them together.
[n1] In game theory, a fact is common knowledge when everyone knows it, everyone knows that everyone knows it, and so on without limit — the standard formalization is due to Robert Aumann. Coordination frequently turns on this higher-order layer rather than on the base fact alone. ↩