The Theory of Everything vs the Theory of Anything

TL;DR

This paper examines the limitations of observational data in defining a unique 'Theory of Everything' and explores how different inflation potentials could produce similar observable universes, highlighting the importance of understanding what can be inferred about the universe.

Contribution

It introduces a framework to assess the naturalness of inflation potentials and discusses how various potentials might lead to similar observable outcomes, emphasizing the limits of current observational constraints.

Findings

Different inflaton potentials can produce universes similar to ours.

Conditional probability questions can help measure the naturalness of inflation models.

Observational data may be insufficient to uniquely determine the underlying theory.

Abstract

To what extent can our limited set of observations be used to pin down the specifics of a ``Theory of Everything''? In the limit where the links are arbitrarily tenuous, a ``Theory of Everything'' might become a ``Theory of Anything''. A clear understanding of what we can and can not expect to learn about the universe is particularly important in the field of particle cosmology. The aim of this article is to draw attention to some key issues which arise in this context, in the hopes of fostering further discussion. In particular, I explore the idea that a variety of different inflaton potentials may contribute to worlds ``like ours''. A careful examination of the conditional probability questions we can ask might give a physical measure of what is ``natural'' for an inflation potential which is quite different from those previously used.