Abstract

The ``Lambda cold dark matter’’ (LCDM) cosmological model (where Lambda stands for Einstein’s cosmological constant and CDM for cold dark matter) is one of the great achievements in Physics of the past forty years. Theoretical predictions formulated in the 1980s turned out to agree remarkably well with measurements, performed decades later, of the galaxy distribution and the temperature structure of the cosmic microwave background radiation. Yet, these successes do not inform us directly about the nature of the dark matter or the dark energy which are the two cornerstones of the model. In recent years a number of observations have suggested possible discrepancies with LCDM both on large and small scales. On large scales results from the DESI galaxy survey seem inconsistent with Lambda and suggest instead an evolving dark energy. On small scales, the abundance of satellite galaxies in the Milky Way and the discovery of bright galaxies at very early times by the James Webb Space telescope are often interpreted as challenges to the standard model.