The Cosmic Microwave Background and Earth's Core-Mantle Boundary: A Tale of Two CMBs
نویسنده
چکیده
The published uncertainties of estimates of cosmic microwave background (CMB) heterogeneity based on the Cosmic Background Explorer (COBE) differential microwave radiometer (DMR) experiment are much too small: they neglect a systematic modelling error that can exceed the estimates. The same systematic modelling error pervades images of the topography of Earth's core-mantle boundary (also called the CMB) from earthquake travel-time data. In both problems, parametric models (truncated spherical harmonic expansions and/or pixel representations) have been fit by least-squares to noisy, unevenly distributed data on the sphere. The part of the "true" CMB that can not be expressed in the parametric representation gives rise to a systematic error that is formally infinite, unless additional constraints beyond the data are imposed. Even with optimistic assumptions about the neglected terms, the total uncertainty is comparable to the published structure. Inferences about individual spherical harmonic coefficients, about overall spectral shapes, and about pointwise values are all affected.
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