Astronomy and Astrophysics<\/a><\/strong>.<\/p>\nARTICLE CONTINUES BELOW AD<\/b>ARTICLE CONTINUES BELOW AD<\/b><\/p>\n
\u201cThis is the dream of every physicist. Find something wrong in our understanding so we can discover something new and profound,\u201d added assistant professor of physics at the Stony Brook University and one of the study\u2019s corresponding authors Simon Birrer.<\/p>\n
A constant in question questioned constantly<\/p>\n
Coined by astronomer Edwin Hubble \u2014 who first calculated it in 1929 \u2014 the Hubble Constant is the rate at which the universe expands. This number reveals not only the universe\u2019s current speed of growth, but also its age and history.<\/p>\n
Nearly a century later, scientists still can\u2019t agree on its exact value.<\/p>\n
The Hubble Constant can be measured in two ways \u2014 one probing the universe at early times and another probing the universe at times near today.<\/p>\n
The early universe probe, which uses cosmological models to indirectly provide the current expansion rate of the universe, favors an expansion rate of ~67 km\/s\/Mpc; and the late (nearby) universe probe, which measures the local universe as it exists today favors an expansion rate of 73 km\/s\/Mpc.<\/p>\n
Measurements based on the nearby universe differ from predictions drawn from the early universe, resulting in what is famously known as the Hubble Tension.<\/p>\n
Confirming this tension would force scientists to rethink the very makeup of the cosmos; perhaps revealing new particles, or evidence for an \u201cearly dark energy\u201d phase that briefly accelerated expansion after the Big Bang.<\/p>\n
Astronomers stress the importance of multiple independent methods to crosscheck the result because the implications are so profound.<\/p>\n
\u201cThis is significant in that cosmology as we know it may be broken,\u201d said Keck Observatory Chief Scientist and Deputy Director John O\u2019Meara in the release. \u201cIf it is true that the Hubble Tension isn\u2019t a mistake in the measurements, we will have to come up with new physics.\u201d<\/p>\n
A new way to measure the universe<\/p>\n
The team used a method called time-delay cosmography to make this precise measurement.<\/p>\n
ARTICLE CONTINUES BELOW AD<\/b><\/p>\n
Much like a funhouse mirror bends and distorts reflections, massive galaxies bend the light of more distant galaxies and quasars, producing multiple images of the same object.<\/p>\n
Animation of the findings by researchers who used time-delay cosmography to independently confirm that the universe\u2019s current rate of expansion, known as the Hubble constant, does not match values predicted from measurements from the universe when it was much younger. (Credit: W. M. Keck Observatory\/Adam Makarenko)<\/strong><\/p>\nWhen the distant object\u2019s brightness changes, astronomers can measure how long it takes those changes to appear in each image. Those \u201ctime delays\u201d act like cosmic yardsticks \u2014 allowing scientists to calculate distances across the universe and, ultimately, determine how fast it\u2019s expanding.<\/p>\n
Keck Observatory\u2019s Cosmic Web Imager\u2019s powerful spectroscopy was essential to the measurement. By observing the motion of stars within the lensing galaxies, the instrument revealed how massive those galaxies are and how strongly they bend light, critical information for pinning down the Hubble Constant.<\/p>\n
\u201cThe key breakthrough relied on the motion of stars in the lens galaxies as measured via Keck\/JWST\/VLT spectroscopy to address the main source of uncertainty, known as the mass-sheet degeneracy,\u201d said postdoctoral fellow at University of Chicago and study corresponding author Anowar Shajib in the release. \u201cThe result also relies on long-term collaborative work between observatories including time delay measurements from 20 years of photometric data obtained at [European Southern Observatory] in Chile.\u201d<\/p>\n
The quest continues<\/p>\n
The team\u2019s measurement currently achieves 4.5% precision \u2014 an extraordinary feat, but not yet enough to confirm the discrepancy beyond doubt.<\/p>\n
The next goal is to refine that precision to better than 1.5%, a level of certainty \u201cprobably more precise than most people know how tall they are,\u201d noted postdoctoral fellow at ETH Zurich and the third corresponding author of the study Martin Millon in the release.<\/p>\n
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![\"\"](\"https:\/\/cdn.bigislandnow.com\/file\/bigislandnow\/2025\/12\/Universe-expansion-rate-from-WM-Keck-Observatory-website.jpg\")
<\/a>Researchers using time-delay cosmography independently confirmed that the universe\u2019s current rate of expansion, known as the Hubble constant, does not match values predicted from measurements from the universe when it was much younger. This \u201cHubble tension\u201d could point to new physics governing the universe. (Image Credit: W. M. Keck Observatory\/Adam Makarenko)<\/p>\n