Scientists with the Dark Energy Spectroscopic Instrument (DESI), an international research collaboration, presented new evidence Wednesday that bolstered its recent finding that dark energy is not inexorably pushing the universe apart at a constant rate of acceleration but rather ebbs and flows and appears to be weakening.

Dark energy is a mystery so daunting that it stretches and strains our most robust theories. The universe is expanding, driven by the unknown force that we've named Dark Energy. Dark Energy is also accelerating the rate of expansion.