Unveiling a fast (and furious) early universe with JWST

JWST observations reveal sources earlier and brighter than anticipated. This talk examines their implications for cosmological and galaxy-formation models. It considers the unexpectedly numerous galaxies during the first few hundred million years, at redshifts above nine, and how cosmological clustering measurements can distinguish competing explanations. It then presents an initial empirical measurement of the dependence of star-formation variability, or burstiness, on galaxy mass, which may help explain the excess. Finally, it discusses tensions between JWST measurements of reionization and evidence from the cosmic microwave background and Lyman-alpha forest, including implications for DESI’s recent dark-energy results.