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1. Traversable Wormhole

   Linked via "Big Rip singularity"

   To keep the throat of a wormhole open against the immense attractive force of gravity, the throat structure must be supported by matter or fields exhibiting negative energy density, often referred to generically as exotic matter. The stress-energy tensor of this material must violate the NEC, meaning $T_{\mu\nu} k^\mu k^\nu < 0$ for some null vector $k^\mu$.
   The constraint imposed by the violation of the NEC on the Equation of State parameter ($w = p/\rho$) is generally $w < -1/3$ [4]. Regions exhibiting $w < -…