Distributed knowledge: Difference between revisions

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== Example ==

The logicians Alice and Bob are sitting in their dark office wondering whether or not it is raining outside. Now, none of them actually knows, but Alice knows something about her friend Carol, namely that Carol wears her bluered coat [[if and only if]] it is raining. Bob does not know this, but he just saw Carol, and noticed that she was wearing her bluered coat. Even though none of them knows whether or not it is raining, it is ''distributed knowledge'' amongst them that it is raining. If either one of them tells the other what they know, it will be clear to the other that it is raining.

If we denote by <math>\varphi</math> that Carol wears a blue coat and with <math>\varphi \implies \psi</math> that if Carol wears a red coat, it is raining, we have

Distributed knowledge is related to the concept [[The Wisdom of the Crowds]]. Distributed knowledge reflects the fact that "no one of us is as smart as all of us."

: <math>(K_b\varphi \land K_a(\varphi \implies \psi)) \implies D_{a,b}\psi</math>

Directly translated: Bob knows that Carol wears a red coat and Alice knows that if Carol wears a red coat it is raining so together they know that it is raining.

In contrast, [[common knowledge]] refers to knowledge that all agents know, all agents know all agents know, all agents know all agents know all agents know, ad infinitum. Distributed knowledge is often confused with the term [[dispersed knowledge]] from economics. However, dispersed knowledge is information that is widely available, and hence more like common knowledge.

Distributed knowledge is related to the concept [[The Wisdom of the Crowds]]. Distributed knowledge reflects the fact that "no one of us is as smart as all of us."