For the proceedings of the 200th course of the International School of Physics "Enrico Fermi", Varenna, 2018.

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Douglas Scott

Dept. of Physics & Astronomy, Univ. of British Columbia, Vancouver, Canada

Summary: The status of the standard cosmological model, also known as “ΛCDM” is described. With some simple assumptions, this model fits a wide range of data, with just six (or seven) free parameters. One should be skeptical about this claim, since it implies that we now have an astonishingly good picture of the statistical properties of the large-scale Universe. However, the successes of the model cannot be denied, including more than 1000 σ worth of detection of CMB anisotropy power. The model is older than most modern astrophysicists seem to appreciate, and has not fundamentally changed for more than a quarter of a century. Tensions and anomalies are often discussed, and while we should of course be open to the possibility of new physics, we should also be skeptical of the importance of 2–3 σ differences between data sets until they become more significant. Still, today's SMC is surely not the full story and we should be looking for extensions or new ingredients to the model, guided throughout by a skeptical outlook.

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