Making up 70% of the universe and responsible for its accelerated expansion, Dark energy is the biggest mystery in cosmology. A simple model where dark energy is described as a cosmological constant explains most of the observations of the past 20 years. However, recent results are challenging this model.  The Dark Energy Spectroscopic Instrument (DESI) is building the largest 3D map of our universe to measure its expansion history over the past 11 billion years, and thereby, study dark energy. The DESI first-year results find tantalizing hints of time-varying dark energy that, if confirmed, would revolutionize the standard model of cosmology. After a brief introduction of the observations that led to our current understanding of cosmology, I will present DESI, explain how it addresses the question of the nature of dark energy, and describe the recent results and their implication. 

Coffee and tea served at 16:00pm