Dark energy and cosmology from the first data release of DESI

The Dark Energy Spectroscopic Instrument (DESI) is the first of a new generation of “Stage-IV” cosmology survey experiments to be collecting data. I will describe the experiment and the cosmological results obtained from the first data release (DR1) – this includes redshifts for more than 6 million galaxies and quasars, a factor of 3x larger than for the previous biggest such survey. These data allow us to precisely measure the expansion rate of the Universe over the last 11 billion years. DESI results released in April 2024 were based on observations of the baryon acoustic oscillation feature, and showed tantalising evidence in favour of a time-varying dark energy equation of state, rejecting the cosmological constant at between 2.5 sigma and 3.9 sigma significance, depending on combinations with external datasets. I will describe these results as well as new ones based on the “full-shape” of the clustering power spectrum including redshift-space distortions, released in November. Apart from reflecting on dark energy, I will discuss the implications of DESI results for the Hubble constant, the neutrino mass scale and tests of general relativity.