Natural Halting Probabilities, Partial Randomness, and Zeta Functions

TL;DR

This paper introduces the zeta number and classifies Turing machines based on their zeta values, exploring their randomness properties and establishing connections with classical and partial randomness concepts.

Contribution

It defines the zeta number and classifies Turing machines into divergent, convergent, and tuatara, proving the existence of universal machines in these classes and analyzing their randomness.

Findings

The zeta number of a universal tuatara machine is c.e. and random.

Introduces asymptotic randomness as a new form of partial randomness.

Shows asymptotic randomness can be characterized by plain complexity.

Abstract

We introduce the zeta number, natural halting probability and natural complexity of a Turing machine and we relate them to Chaitin's Omega number, halting probability, and program-size complexity. A classification of Turing machines according to their zeta numbers is proposed: divergent, convergent and tuatara. We prove the existence of universal convergent and tuatara machines. Various results on (algorithmic) randomness and partial randomness are proved. For example, we show that the zeta number of a universal tuatara machine is c.e. and random. A new type of partial randomness, asymptotic randomness, is introduced. Finally we show that in contrast to classical (algorithmic) randomness--which cannot be naturally characterised in terms of plain complexity--asymptotic randomness admits such a characterisation.