The Hubble tension, the stubborn discrepancy between two methods of measuring how fast the universe is expanding, has long haunted modern physics. Some scientists hoped it would eventually dissolve into measurement error. New findings suggest it will not.
To understand what’s at stake, a brief step back is necessary. In the 1920s, astronomer Edwin Hubble discovered that the universe was expanding, a conclusion drawn from studying the redshift of distant galaxies. Then, in the late 1990s, observations of Type Ia Supernovae, celestial events prized for their consistent peak luminosity, which makes them reliable “standard candles“, revealed something even more startling: the universe wasn’t just expanding, it was accelerating. The question of exactly how fast became the next frontier.
A Measurement Built on Redundancy, Not Just Precision
The new study, led by the H0 Distance Network (H0DN) Collaboration and published in the journal Astronomy & Astrophysics, arrives at a Hubble constant of 73.50 ± 0.81 km/s/Mpc, a margin of error of less than one percent. What distinguishes this result from its predecessors isn’t only its precision, but its architecture.
Rather than anchoring the measurement to a single technique, the team constructed what they describe as a “distance network“, a web of overlapping, independent methods that check and validate one another. These included Cepheid variable stars, the same type used by Hubble himself a century ago, alongside red giant stars and certain luminous galaxies. Data came from a global network of observatories, among them the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile and the NSF Kitt Peak National Observatory in Arizona.
The redundancy was deliberate and revealing. When researchers removed any single method from the analysis, the results stayed nearly unchanged. According to coauthor Adam Riess of Johns Hopkins University, speaking to NASA, “the power of this work is that it doesn’t depend on any single method. When multiple, independent measurements all point to the same answer, it strengthens the case that we’re seeing a real feature of the universe, not a flaw in one technique.”
This graphic provides an overview of the Local Distance Network, the research team’s new tool to integrate diverse measurements of the Hubble constant into a coherent, rig-orous framework – © Fabio Crameri (ISSI Bern), based on the original by Richard I. Anderson and the H₀DN Collaboration (2025) / NASA.
What the Standard Model Isn’t Accounting For
The tension, as the study’s authors put it, “may point to new physics beyond the standard cosmological model.” That’s a significant statement. The standard model, for all its predictive success, does not fully account for dark energy, new particles, or potential modifications to gravity. According to NSF’s NOIRLab, a member of the H0DN collaboration, these omissions matter: when scientists extrapolate from the Cosmic Microwave Background to the universe as it exists today, any unknown factor that was present during cosmic evolution would distort that extrapolation.
In concrete terms, the universe we observe appears to be expanding faster than the universe we calculate from its earliest moments. The authors were unambiguous about the implications: “This work effectively rules out explanations of the Hubble tension that rely on a single overlooked error in local distance measurements. If the tension is real, as the growing body of evidence suggests, it may point to new physics beyond the standard cosmological model.“
Complete Distance Network, with all possible pathways illustrated. Anchors are objects that establish an absolute scale based on the methods shown to their left – © Astronomy & Astrophysics
Open Data and the Road Ahead
One notable feature of the H0DN study is that the collaboration made their full dataset publicly available. The intention is to allow future researchers to refine, challenge, and build upon the findings, a gesture toward collective scientific progress rather than a closed result.
That future work will have powerful new tools at its disposal. The Nancy Grace Roman Space Telescope, an infrared observatory currently scheduled for launch in 2027, is designed to investigate not only cosmic distances but also dark energy, dark matter, and exoplanets. Its data streams are expected to bring a new level of resolution to the very questions this study has sharpened.
Baseline Distance Network illustrated analogously to the previous figure – © Astronomy & Astrophysics
According to Popular Mechanics, the new result does not resolve the Hubble tension. What it does is remove a comfortable escape route, the possibility that the discrepancy was simply a measurement artifact. The tension remains. The universe, it seems, has something left to tell us.