From Hadrons to Gravitons via Strings

TL;DR

This paper reviews the historical development of string theory, highlighting its unexpected emergence as a candidate for a unified quantum theory of gravity and other fundamental forces over the past fifty years.

Contribution

It provides a historical overview of string theory's evolution from hadron models to a candidate for quantum gravity, emphasizing its conceptual breakthroughs and current status.

Findings

String theory predicts gravity and extra dimensions due to consistency requirements.

The string tension must be vastly larger than initially thought for unification.

String theory has evolved into a comprehensive framework for fundamental physics.

Abstract

The first quantum string theories were developed around 1970, prior to the discovery of QCD, with the goal of producing a theory of hadrons. Basic physical requirements and mathematical consistency of the string theories known at that time turned out to require the inclusion of gravity and the existence of extra spatial dimensions. This came as a complete surprise to everyone who was involved. It led to a completely new and very ambitious goal for string theory research, namely a unified quantum theory of gravity and all other forces. In particular, this goal requires that the string tension is 20 orders of magnitude larger than was previously envisioned. Fifty years later, this goal is widely shared.