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A 2025 analysis using eight gravitationally lensed quasars offers an independent way to measure how quickly the universe expands. Its result, reported as more consistent with other present-day measurements than with estimates inferred from the early universe, adds evidence to the Hubble tension—but does not resolve it or prove that new physics is responsible.
What is the Hubble tension?
The Hubble constant describes the universe’s current expansion rate. Estimates based on observations of the nearby, relatively recent universe have tended to differ from values inferred from observations of the early universe. That persistent mismatch is known as the Hubble tension.
As rounded context, SciTechDaily gives approximately 73 km/s/Mpc for nearby-galaxy measurements and approximately 67 km/s/Mpc for estimates based on the cosmic microwave background (CMB). These are illustrative values, not the exact result of the new lensing analysis. The approaches also depend on different observations and assumptions:
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- CMB inference: uses observations of the early universe and a cosmological model to infer what the expansion rate is today.
- Time-delay cosmography: uses light from distant quasars bent by foreground galaxies, along with models of those galaxies, to estimate the expansion rate through a separate route.
How can a lensed quasar measure expansion?
A massive foreground galaxy can bend light from a more distant quasar into several visible images. The light does not take identical routes through the gravitational field, so changes in the quasar’s brightness appear in each image at different times. Researchers measure those time delays and combine them with a model of the foreground galaxy’s mass distribution to infer the Hubble constant. This technique is called time-delay cosmography.
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The approach provides a cross-check that does not rely on the same chain of nearby distance calibrations as the local distance ladder or the same early-universe inference as CMB measurements. It is not assumption-free: interpreting the delays depends on how accurately researchers model the lens galaxy and its mass.
What did the 2025 analysis find?
The paper identified in the coverage, “TDCOSMO 2025: Cosmological constraints from strong lensing time delays,” analyzed eight time-delay lens systems. University of Tokyo coverage reports about 4.5% precision and says the measurement is more consistent with other present-day observations than with early-universe measurements. The accessible coverage does not establish the paper’s exact central value or uncertainty interval, so the rounded 73 and 67 km/s/Mpc figures should not be mistaken for the study’s result.
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The same coverage says roughly 1–2% precision would be needed to decisively test the tension. At about 4.5%, this analysis is a useful independent measurement, but not a decisive verdict. The foreground galaxies’ mass profiles are a significant modeling uncertainty because different assumptions about the mass distribution can affect the inferred expansion rate. Adding more lens systems and refining those models are ways researchers can improve the measurement.
Does this solve the Hubble tension or prove new physics?
No. The finding adds a measurement that leans toward the pattern seen in other present-day estimates, which is relevant evidence. But its reported precision is not yet enough to settle the discrepancy, and a result that favors one side does not by itself establish why the measurements disagree. The tension could reflect new physics, unaccounted-for measurement or modeling effects, or some combination; this study alone does not distinguish among those possibilities.
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SciTechDaily’s 10 December 2025 report attributes to Kenneth Wong, a University of Tokyo Project Assistant Professor, the view that the result is more consistent with current-day observations and less consistent with early-universe measurements. It also quotes postdoctoral researcher Eric Paic saying that increasing the sample size is the next step toward improving precision. Those statements describe the researchers’ interpretation and goal, not proof that the tension has a particular cause.
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The immediate challenge is to make time-delay cosmography more precise. Researchers can expand the sample beyond the eight systems in this analysis and improve how they model lens-galaxy mass distributions. If independent methods converge as their uncertainties shrink, the disagreement may diminish; if a robust mismatch persists, it will provide stronger grounds for investigating whether the standard picture of cosmology is incomplete.
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The study is identified in the coverage as published in Astronomy & Astrophysics on 5 December 2025, under the title “TDCOSMO 2025: Cosmological constraints from strong lensing time delays” (DOI 10.1051/0004-6361/202555801). The DOI record is available at doi.org/10.1051/0004-6361/202555801. The method, numerical context and quoted remarks described here are reported in SciTechDaily’s 10 December 2025 coverage of the University of Tokyo research.
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