  We investigate signal propagation in a quantum field simulator of the
Klein-Gordon model realized by two strongly coupled parallel one-dimensional
quasi-condensates. By measuring local phononic fields after a quench, we
observe the propagation of correlations along sharp light-cone fronts. If the
local atomic density is inhomogeneous, these propagation fronts are curved. For
sharp edges, the propagation fronts are reflected at the system's boundaries.
By extracting the space-dependent variation of the front velocity from the
data, we find agreement with theoretical predictions based on curved geodesics
of an inhomogeneous metric. This work extends the range of quantum simulations
of non-equilibrium field dynamics in general spacetime metrics.
