---
title: "Uncanny Index"
description: "The formal instrument proposed in Traversing the Uncanny Ridge for locating novelty between systems."
type: "glossary-term"
canonical_url: "https://antikythera.wiki/terms/uncanny-index"
md_url: "https://antikythera.wiki/md/terms/uncanny-index"
last_updated: "2026-09-06"
site: "Antikythera Wiki"
---

# Uncanny Index

> A working definition written for this wiki from the reading notes; not Antikythera's own wording. From Antikythera Wiki (https://antikythera.wiki/terms/uncanny-index), an independent guide to Antikythera's published work.

The formal instrument proposed in *Traversing the Uncanny Ridge* for locating novelty between systems. Take a pair of systems' joint output (X, Y) and an observer's prior density *p*; Bayesian surprise is E[−log p(X,Y)]. The uncanny index Δ((X,Y), p) is the expected change in that surprise relative to a *null-protocol* counterpart — the same pair run independently — so positive Δ means the interaction made outputs less expected than independence, negative Δ means hyper-convergence. Sup and inf over all admissible pairs give upper and lower indices for a protocol. It makes novelty explicitly perspectival (a function of *p*) and, by itself, cannot tell novelty from noise — the "ridge" is a peak between collapse and chaos that the formula does not encode.

## Appears in

- [Traversing the Uncanny Ridge: Searching for Novelty in Intersystemic Communication](https://antikythera.wiki/work/journal/coginfra/traversing-the-uncanny-ridge) (2025-05-10)

_Glossary generated 2026-09-06._