Polarization of the CMB

Can make power spectra from the E and B patterns on the sphere just as for the total intensity - and also for the TE cross power spectrum.

For given input cosmological parameters theory predicts T, E, B and TE spectra.

Same mechanism which gives T gives E and TE.

Gravity waves effect all spectra, but based on existing T data we know contribution very small.

So we know basically what to expect
...if it doesn't match the whole framework falls apart! Critical test!