The Stephani Universe, K-Essence and Strings in the 5th Dimension

The Stephani universe is an inhomogeneous alternative to ΛCDM. We show that the exotic fluid driving the Stephani exact solution of Einstein’s equations is an unusual form of k-essence that is linear in “velocity”. Much as the Stephani universe can be embedded into (a section of) flat 5-d Minkowski space-time, we show that the k-essence obtains through dimensional reduction of a 5-d strongly coupled non-linear “electrodynamics” that, in the empty Stephani universe, corresponds to space filling magnetic branes in string/M-theory.