A long-awaited study of the cosmic expansion rate suggests that when it comes to the Hubble tension, cosmologists are still missing something.
Nearly a century ago, Edwin Hubble discovered that the universe is getting larger. Modern measurements of how fast it is expanding disagree, however, suggesting that our understanding of the laws of physics might be off. Everyone expected the sharp vision of the James Webb Space Telescope to bring the answer into focus. But a long-awaited analysis of the telescope’s observations released late Monday evening once again gleans conflicting expansion rates from different types of data, while homing in on possible sources of error at the heart of the conflict.Two rival teams have led the effort to measure the cosmic expansion rate, which is known as the Hubble constant, or H0. One of these teams, led by Adam Riess of Johns Hopkins University, has consistently measured H0 to be about 8% higher than the theoretical prediction for how fast space should be expanding, based on the cosmos’s known ingredients and governing equations. This discrepancy, known as the Hubble tension, suggests that the theoretical model of the cosmos might be missing something — some extra ingredient or effect that speeds up cosmic expansion. Such an ingredient could be a clue to a more complete understanding of the universe.