# Everett's Missing Postulate and the Born Rule

## TL;DR

This paper formulates two postulates for Everett's Relative State Interpretation, deriving the Born rule and standard quantum postulates from a more physically grounded framework using decoherence.

## Contribution

It introduces two postulates that connect the mathematical formalism to physical reality and derives the Born rule without relying on uncertainty, advancing Everett's interpretation.

## Key findings

- Derivation of the Born rule from the new postulates
- Connection of the density function to physical location distributions
- Elimination of the need for uncertainty in quantum probabilities

## Abstract

Everett's Relative State Interpretation has gained increasing interest due to the progress of understanding the role of decoherence. In order to fulfill its promise as a realistic description of the physical world, two postulates are formulated. In short they are 1) for a system with continuous coordinates $\vec{x}$, discrete variable $j$, and state $\psi_j(\vec{x})$, the density $\rho_j(\vec{x})=|\psi_j(\vec{x})|^2$ gives the distribution of the location of the system with the respect to the variables $\vec{x}$ and $j$; 2) an equation of motion for the state $i\hbar \partial_t \psi = H\psi$. The first postulate connects the mathematical description to the physical reality, which has been missing in previous versions. The contents of the standard (Copenhagen) postulates are derived, including the appearance of Hilbert space and the Born rule. The approach to probabilities earlier proposed by Greaves replaces the classical probability concept in the Born rule. The new quantum probability concept, earlier advocated by Deutsch and Wallace, is void of the requirement of uncertainty.