  Power spectra and cross-correlation measurements from the weak gravitational
lensing of the cosmic microwave background (CMB) and the cosmic shearing of
faint galaxies images will help shed light on quantities hidden from the CMB
temperature anisotropies: the dark energy, the end of the dark ages, and the
inflationary gravitational wave amplitude. Even with modest surveys, both types
of lensing power spectra break CMB degeneracies and they can ultimately improve
constraints on the dark energy equation of state w by over an order of
magnitude. In its cross correlation with the integrated Sachs-Wolfe effect, CMB
lensing offers a unique opportunity for a more direct detection of the dark
energy and enables study of its clustering properties. By obtaining source
redshifts and cross-correlations with CMB lensing, cosmic shear surveys provide
tomographic handles on the evolution of clustering correspondingly better
precision on the dark energy equation of state and density. Both can indirectly
provide detections of the reionization optical depth and modest improvements in
gravitational wave constraints which we compare to more direct constraints.
Conversely, polarization B-mode contamination from CMB lensing, like any other
residual foreground, darkens the prospects for ultra-high precision on
gravitational waves through CMB polarization requiring large areas of sky for
statistical subtraction. To evaluate these effects we provide fitting formula
for the evolution and transfer function of the Newtonian gravitational
potential.
