Wayne Hu developed physical descriptions of Cosmic microwave background anisotropy, including the 1997 damping-tail analysis with Martin White. Their work calibrated photon-diffusion and reionization damping while separating model-dependent changes in acoustic structure.[ref]
Photon diffusion smooths fluctuations on scales photons traverse before decoupling. Its angular imprint therefore connects microscopic scattering and the expansion history to the measured small-scale Cosmic microwave background anisotropy.
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