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

__F. S. N. Lobo__

**Resumo**

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 (NEC). 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 nonstandard wormhole geometries, fundamentally different from their counterparts in general relativity (GR). We explore interesting features of these geometries, in particular, the physical properties and characteristics of these ‘exotic spacetimes’.

**Palavras chave**

Traversable wormholes, energy conditions, geons, modified gravity, Spacetime topology causal structure spinor structure, Modified theories of gravity

**International Journal of Modern Physics D**

Volume 25

maio 2016

**DOI:** 10.1142/S0218271816300172**Código bibliográfico ADS:** 2016IJMPD..2530017L