The James Webb Space Telescope, working alongside Hubble, has uncovered an unsettling contradiction about how fast the universe is expanding. These new findings — which challenge decades of accepted data — could force scientists to rethink how we measure the cosmos and even rewrite the fundamentals of modern cosmology.
In early 2024, the James Webb and Hubble telescopes together confirmed one of physics’ most perplexing mysteries: the universe appears to be expanding at different rates depending on how it’s observed. Known as the Hubble tension, this discovery calls into question the foundation of our current understanding — and could upend modern science as we know it.
Confirmation of a cosmic puzzle
Hubble first detected this discrepancy back in 2019, revealing that different measurement methods yielded conflicting results. But it wasn’t until Webb joined the effort that scientists could confirm, with unprecedented precision, that the anomaly is real. A joint study between the two telescopes has now ruled out any possibility of measurement error. The findings, published February 6 in The Astrophysical Journal Letters, suggest that our standard model of the universe may need serious revision.
Adam Riess, Nobel laureate and astrophysicist at Johns Hopkins University, put it plainly: “With measurement errors ruled out, what’s left is the exciting — and daunting — possibility that we’ve misunderstood the universe.”
The James Webb telescope could prove that we may have been completely wrong about the Universe. © Mark Garlick, Science Photo Library
Two methods, two different results
The Hubble constant — the number that defines the universe’s expansion rate — can be calculated in two ways.
The first method examines tiny fluctuations in the cosmic microwave background, the faint afterglow of the Big Bang observed by the Planck satellite between 2009 and 2013. This approach gives a value of about 67 kilometers per second per megaparsec (km/s/Mpc).
The second relies on Cepheid variable stars to map distances across space. By comparing their true brightness to how bright they appear from Earth, astronomers can determine their distance — and in turn, how fast the universe is stretching. Riess’s team measured a rate closer to 74 km/s/Mpc, noticeably faster than the value derived from the cosmic microwave background.
A cosmological crisis
This widening gap between methods led Nobel laureate David Gross to call it a “crisis” in cosmology during a 2019 conference in California. The failure to reconcile these numbers suggests that our understanding of dark matter, dark energy, and perhaps even the very fabric of space-time might be incomplete.
In 2023, Riess’s team expanded their analysis, observing more than 1,000 additional Cepheid stars across five galaxies up to 130 million light-years away. By comparing data from both Webb and Hubble, the researchers confirmed their previous results — ruling out measurement error once and for all.
Implications for the future
The confirmation of the Hubble tension by Webb and Hubble forces cosmologists to face fundamental questions about how the universe works. Ongoing studies aim to explain this discrepancy and test new theories that might rewrite what we know about the cosmos.
Far from solving cosmic mysteries, each new discovery seems to reveal just how much we don’t yet understand. These findings highlight both the importance of relentless scientific exploration and the thrill of uncovering the unknown.
In the end, the universe keeps surprising us — and humbling us. The Hubble tension remains a vivid reminder that even our most advanced tools can expose how little we truly know, urging scientists worldwide to rethink and redefine the future of cosmology.
