From the Flamm-Einstein-Rosen bridge to the modern renaissance of traversable wormholes

TL;DR

This paper explores the theoretical foundations and properties of traversable wormholes and related exotic spacetimes, emphasizing how modified gravity theories can support such structures without violating energy conditions.

Contribution

It reviews the evolution of wormhole concepts from classical to modern theories, highlighting how higher-order curvature terms enable traversable wormholes in modified gravity.

Findings

Higher-order curvature terms support wormholes without exotic matter

Modified gravity allows energy conditions to be satisfied

Distinct physical properties of exotic spacetimes are analyzed

Abstract

We consider the possibility of multiply-connected spacetimes, ranging from the Flamm-Einstein-Rosen bridge, geons, and the modern renaissance of traversable wormholes. A fundamental property in wormhole physics is the flaring-out condition of the throat, which through the Einstein field equation entails the violation of the null energy condition. In the context of modified theories of gravity, it has also been shown that the normal matter can be imposed to satisfy the energy conditions, and it is the higher order curvature terms, interpreted as a gravitational fluid, that sustain these non-standard wormhole geometries, fundamentally different from their counterparts in general relativity. We explore interesting features of these geometries, in particular, the physical properties and characteristics of these `exotic spacetimes'.