CMB polarization and gravity waves The CMB not only has a tempera- ture, but also polarization –Just like ordinary light Polarization is created by local quadrupoles in the temperature field Gravity waves create local quadru- poles by (stretching space + Doppler shift) –Lots of other effects, too, but this is the cool one Therefore, we can in principle observe gravity waves from the Big Bang by looking for a particular signature in the CMB polarization –But the amplitude is low, probably at ~100 nK RMS compared to a 3K carrier signal
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