# Copernicanism and the Typicality in Time

## TL;DR

This paper critically examines the assumption of temporal typicality in cosmology and astrobiology, arguing that unlike spatial typicality, temporal typicality is inherently vague and cannot be precisely defined.

## Contribution

It highlights the uncritical use of temporal typicality assumptions and defends the position that such typicality in time is fundamentally ill-defined and limited in scope.

## Key findings

- Temporal typicality is inherently vague and cannot be precisely defined.
- The paper challenges the uncritical use of temporal typicality in scientific reasoning.
- It suggests that temporal typicality could be made more precise with additional contextual constraints.

## Abstract

How special (or not) is the epoch we are living in? What is the appropriate reference class for embedding the observations made at the present time? How probable -- or else -- is anything we observe in the fulness of time? Contemporary cosmology and astrobiology bring those seemingly old-fashioned philosophical issues back into focus. There are several examples of contemporary research which use the assumption of typicality in time (or temporal Copernicanism) explicitly or implicitly, while not truly elaborating upon the meaning of this assumption. The present paper brings attention to the underlying and often uncritically accepted assumptions in these cases. It also aims to defend a more radical position that typicality in time is not -- and cannot ever be -- well-defined, in contrast to the typicality in space, and the typicality in various specific parameter spaces. This, of course, does not mean that we are atypical in time; instead, the notion of typicality in time is necessarily somewhat vague and restricted. In principle, it could be strengthened by further defining the relevant context, e.g., by referring to typicality within the Solar lifetime, or some similar restricting clause.