Evidence mounts that universe's dark energy is changing over time

New data involving millions of galaxies and luminous galactic cores is providing fresh evidence that the enigmatic and invisible cosmic force called dark energy - responsible for the universe's accelerated expansion - has weakened over time rather than remaining constant, as long hypothesized. The findings announced on Wednesday are part of a years-long study of the history of the cosmos, focusing upon dark energy. The researchers analyzed three years of observations by the Dark Energy Spectroscopic Instrument, or DESI, at Kitt Peak National Observatory in Arizona.