What is the distance to the CMB?

Abstract: The success of precision cosmology depends not only on accurate observations, but also on the theoretical model -- which must be understood to at least the same level of precision. Subtle relativistic effects can lead to biased measurements if they are neglected. One such effect gives a systematic shift in the distance-redshift relation away from its background value, due to the non-linear relativistic flux conservation. This leads to an increase of the distance to the last scattering surface by about 1%, reducing the CMB-value of H₀ by about 5% which completely removes the tension with local measurements.
In my talk I give an introduction to cosmological parameter estimation with CMB measurements. Then I show how such measurements depend on the distance to the CMB and finally I explain our recent findings reported in arXiv:1405.7860v2.