A Theory of Everything (ToE) aims to reconcile four fundamental forces. These forces are currently
described by two incompatible frameworks. The first of these frameworks is the Standard Model of
Particle Physics, which accurately describes three of the forces and governs behaviour on microscopic
scales. In contrast, gravity, the fourth fundamental force, is described on a macroscopic level using
Einstein’s theory of general relativity, the second framework. Over the past 100 years, scientists have
endeavoured to reconcile these two frameworks into a ToE; however, no resolution has yet been
identified. The successful development of a ToE would enable scientists to probe the early universe, an
area of physics unaccounted for by current models.
To assess the likelihood that a valid ToE will be discovered, this literature review analyses three
approaches: two historic attempts that sparked significant debate and a contemporary (2025) approach
that may mark a pivotal change in ToE research. To determine the factors influencing the validity of a ToE,
these case studies are evaluated against the criteria of mathematical verifiability, alignment with
established knowledge, and experimental accessibility. However, it does not suffice for a theory to be
proven true, it must also gain majority acceptance within the scientific community. This review, therefore,
also discusses the challenges involved in achieving such acceptance and uses the fluctuating popularity
of string theory to evidence this.