The Atacama Cosmology Telescope’s final polarisation maps reinforce the long-standing Hubble tension, confirming a slower early-universe expansion rate similar to Planck’s findings. By ruling out several proposed fixes, the new data intensifies the mystery and suggests current cosmological models may be missing key physics.The Atacama Cosmology Telescope’s final polarisation maps reinforce the long-standing Hubble tension, confirming a slower early-universe expansion rate similar to Planck’s findings. By ruling out several proposed fixes, the new data intensifies the mystery and suggests current cosmological models may be missing key physics.