Apparently the Internet hasn't noticed this paper yet: http://arxiv.org/abs/1807.04726 Traversable wormholes in four dimensions Juan Maldacena, Alexey Milekhin, Fedor Popov (Submitted on 12 Jul 2018) We present a wormhole solution in four dimensions. It is a solution of an Einstein Maxwell theory plus charged massless fermions. The fermions give rise to a negative Casimir-like energy, which makes the wormhole possible. It is a long wormhole that does not lead to causality violations in the ambient space. It can be viewed as a pair of entangled near extremal black holes with an interaction term generated by the exchange of fermion fields. The solution can be embedded in the Standard Model by making its overall size small compared to the electroweak scale. It avoids time travel paradox by being longer than the normal distance between the ends. If I have read the paper correctly, to realize this within the standard model, you would have a loop of hypercharge flux threading the wormhole, and the negative energy required by the geometry would arise from excitation modes of hypercharged fermion fields that are associated with the loop of flux. To some extent this line of investigation has come from Maldacena & Susskind's "ER = EPR", and I wonder just how small you can make this construction. Can you have a spacetime which is just a network of wormholes? Could such a spacetime be understood in almost graph-theoretic terms? And: this wormhole is said to be equivalent to two entangled black holes - could you build up homogeneous macroscopic spacetime by starting with a network of such wormholes, and then appropriately entangling their endpoints?