For generations, cosmologists have held that dark energy — the invisible engine of cosmic acceleration — is fixed and eternal, a kind of universal constant woven into the fabric of spacetime. Now, the most exhaustive catalog of stellar explosions ever assembled, spanning three thousand supernovas across billions of light-years, is quietly unsettling that assumption. The data suggest dark energy may shift and evolve as the universe ages, placing the standard cosmological model under a pressure it was not designed to withstand. Humanity's picture of where the cosmos is going — and what it ultima