Polarization Predicted - Test the Model

Can make power spectra of 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.

We know T so we know what polarization to expect
...if it doesn't match the whole framework falls apart! Critical test!
Only gravity waves can produce B component. T data sets limits on these such that B should be much smaller than expected E level.