Figure 45: The acoustic power spectrum of the cosmic microwave background as observed by
WMAP [229] together with the a priori predictions of CDM (red line) and no-CDM (blue line)
as they existed in 1999 [265] prior to observation of the acoustic peaks. CDM correctly predicted
the position of the first peak (the geometry is very nearly flat) but over-predicted the amplitude
of both the second and third peak. The most favorable a priori case is shown; other plausible
CDM parameters [468] predicted an even larger second peak. The most important parameter
adjustment necessary to obtain an a posteriori fit is an increase in the baryon density above
what had previously been expected from BBN. In contrast, the no-CDM model ansatz made as a
proxy for MOND successfully predicted the correct amplitude ratio of the first to second peak with
no parameter adjustment [268, 269]. The no-CDM model was subsequently shown to under-predict
the amplitude of the third peak [442].
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