Defending Bayes, Part 4
Clarifying the Foundations of Irreducible Uncertainty
Introduction
In a recent tweet1, Eliezer Yudkowsky succinctly articulated a foundational insight:
"The only true randomness / irreducible uncertainty, is that which results from standing in more than one place and being unable to tell who you are (indexical uncertainty)."
This insight aligns closely with our earlier exploration of empirical knowledge as timeline uncertainty. Here we clarify how "indexical uncertainty" (uncertainty about one's identity or vantage point) directly corresponds to "timeline uncertainty" within the Quantum Branching Universe (QBU) framework.
Defining Indexical Uncertainty
Indexical uncertainty arises when an observer occupies multiple possible states or locations without sufficient information to pinpoint their exact identity or position. It reflects the subjective uncertainty inherent in self-location scenarios, such as:
The Sleeping Beauty problem
Quantum measurement scenarios (e.g., Schrödinger's cat)
Simulation hypotheses and anthropic reasoning
Relating Indexical Uncertainty to Timeline Uncertainty
Within the QBU framework, each observer is inherently uncertain about which precise timeline they inhabit. Timeline uncertainty captures exactly this self-locating ambiguity. Thus, indexical uncertainty and timeline uncertainty represent two descriptions of the same fundamental phenomenon:
Indexical framing: "Who am I, given multiple possible locations or states?"
Timeline framing: "Which timeline am I on, given multiple consistent possibilities?"
Quantum and Philosophical Implications
Understanding the equivalence of indexical and timeline uncertainty offers clarity to philosophical debates surrounding quantum mechanics and subjective probability. Specifically:
It resolves confusion about the nature of quantum randomness by framing it explicitly as uncertainty about timelines.
It enhances the interpretation of quantum decision theory (QDT) by explicitly acknowledging timeline uncertainty as indexical.
Conclusion and Further Exploration
Recognizing the equivalence of indexical and timeline uncertainty provides a robust philosophical and epistemological grounding for interpreting subjective probability and decision-making under uncertainty. Future posts will explore deeper implications for quantum foundations, anthropic reasoning, and practical decision theory.
Yudkowsky, Eliezer. Tweet on indexical uncertainty. February 22, 2024.