# The E\"{o}tv\"{o}s Paradox: The Enduring Significance of E\"{o}tv\"{o}s' Most Famous Paper

## TL;DR

This paper examines the historical and scientific significance of Eötvös' 1922 experiments on the equivalence principle, the subsequent reanalysis suggesting a possible fifth force, and explores potential resolutions to this paradox.

## Contribution

It provides a comprehensive review of the Eötvös paradox, analyzing historical experiments, reanalyses, and proposing new directions for resolving the conflicting evidence.

## Key findings

- Reanalysis of Eötvös' data hints at a possible fifth force.
- Many modern experiments have not confirmed the fifth force.
- The paper discusses the historical link between Eötvös and Einstein.

## Abstract

Following the death of Baron Lor\'{a}nd von E\"{o}tv\"{o}s in 1919, his collaborators Desiderius Pek\'{a}r and Eugen Fekete co-authored a paper in 1922 containing the results of a series of earlier experiments testing the identity of inertial and gravitational mass, the Weak Equivalence Principle (WEP). Although the so-called "EPF" paper made no claim for any WEP violations, a subsequent 1986 reanalysis of the EPF paper revealed a pattern in their data suggesting the presence of a new ("fifth") force in nature. Although the EPF data, and the 1986 reanalysis of these data, present fairly compelling evidence for such a fifth force, many contemporary experiments have failed to detect its presence. Here we summarize the key elements of this "E\"{o}tv\"{o}s paradox," and suggest some possible paths to a resolution. Along the way we also discuss the close relationship between E\"{o}tv\"{o}s and Einstein, and consider how their respective contributions may have been influenced by the other's.