  The Stephani universe is an inhomogeneous alternative to $\Lambda{\rm CDM}$
.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, is similar to the Nielsen-Olesen field
theory of the dual string.
