  We apply CMB lensing techniques to large scale structure and solve for the
3-D cosmic tidal field. We use small scale filamentary structures to solve for
the large scale tidal shear and gravitational potential. By comparing this to
the redshift space density field, one can measure the gravitational growth
factor on large scales without cosmic variance. This potentially enables
accurate measurements of neutrino masses and reconstruction of radial modes
lost in 21 cm intensity mapping, which are essential for CMB and other cross
correlations. We relate the tidal fields to the squeezed limit bispectrum, and
present initial results from simulations and data from the SDSS.
