  We present the first statistically significant detection of cosmic structure
using broadly distributed hydrogen radio emission. This is accomplished using a
cross correlation with optical galaxies. Statistical noise levels of $20 \mu $K
are achieved, unprecedented in this frequency band. This lends support to the
idea that large volumes of the universe can be rapidly mapped without the need
to resolve individual faint galaxies, enabling precise constraints to dark
energy models. We discuss strategies for improved intensity mapping.
