The chapter delves into the Dark Energy Spectroscopic Instrument (DESI) and its findings challenging current cosmological theories on dark energy, a mysterious force driving the universe's accelerated expansion. It explores the concepts of dark energy, vacuum energy, and the variations in dark energy density throughout the universe's history, leading to potential new understandings of the universe's evolution and eventual fate. Scientists face the possibility of reevaluating the standard model of cosmology due to recent surprising revelations from DESI and the implications for the universe's future.