Planck 2018 results
Free Access

Fig. 15.


Successive improvements of the figure of merit FoM ={det[Cov(Ωbh2; Ωch2; τ,As; ns;…)]}−1/2 for various models and data sets, relative to COBE. This shows the relative improvement with respect to the anisotropy discovery experiment, COBE (with first results in 1992). For COBE, we have additionally (anachronistically) assumed a Planck prior on the optical depth 0.055 ± 0.009. The relative reduction of the allowed phase space volume is impressive for all models, with even greater shrinkage in volume for higher-dimensional model extensions. For ΛCDM, the improvement is more than 1010. For the largest model spaces, having four or five additional dimensions compared to ΛCDM, this improvement is more than 1016 in 26 years, corresponding to a 6-month doubling time, three times faster than Moore’s Law! This is one reason why the study of the CMB has allowed us to address more and more ambitious questions with time, a feature that is expected to continue with future experiments.

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