‘Something’s missing’: Most thorough-ever study of the cosmos proves we still can’t explain how the universe is expanding
There is a central crisis in cosmology: Different measurements give different values for the expansion rate of the universe. Now, a comprehensive analysis combining decades of independent measurements suggests that this discrepancy is not due to error or uncertainty; rather, it is a potential path to new physics beyond the standard cosmological model.
Astronomers calculate the rate of expansion of the universe, or Hubble constantin two ways. One method is to use measurements of the distance to the cosmic microwave background (CMB), the first light that propagated only 380,000 years after light appeared. Big Bang. The second method consists of studying the expansion of the local universe, using observations of “standard candles”, nearby stars of known luminosity whose light stretches – or shifts towards the red – when it reaches us.
Although this discrepancy seems small, it is much larger than statistical uncertainty can explain, presenting a puzzling disagreement known as the Hubble tension. So a large symposium of astronomers met to vote on the best methods and data to constrain the Hubble constant and determine whether the tension actually exists.
In the resulting article, published April 10 in the journal Astronomy and astrophysicsthe authors derived the most precise Hubble constant to date and found that the tension persists, suggesting that our current cosmological model is incomplete.
“This is why the Hubble tension is so interesting,” study co-author Richard Andersonastrophysicist at the University of Göttingen, told Live Science by email. “The comparison between the value of the late and early universe of [the Hubble constant] tests basic physics on cosmological scales, and it tells us something is missing. »
The most comprehensive examination of the expanding local universe
Previous cosmological calculations relied on creating a cosmic distance scale. Its levels include increasingly distant celestial objects, notably pulsating Cepheid variable stars in the Milky Way and more distant supernovas, whose distances can be calculated from the difference between their intrinsic luminosity and the luminosity they appear to us after their light has passed through expanding space.
However, this recent community effort, launched in Groundbreaking International Space Science Institute Workshop in Bern, Switzerland in March 2025 expanded the cosmic distance scale into a comprehensive survey of the nearby universe called the Local Distance Network, achieving a lofty goal that was considered “potentially inaccessible“ten years ago.
“This is not just a new value of the Hubble constant,” the researchers explain in a press release. National Science Foundation NOIRLab statement; “This is a community-based framework that brings together decades of independent distance measurements in a transparent and accessible way.”
The unified framework combines decades of independent research using various techniques that may overlap in observations to achieve “redundancy” – an invaluable technique for reducing systematic errors and statistical anomalies.
For example, this allowed the researchers to perform a series of “leave me out” analyses: by excluding a specific technique, such as Cepheid-based calculations, they saw minimal change in the overall results of their newly constrained Hubble constant.
The foundations of a cosmic network
The local distance network is based on anchors – celestial objects whose distances have been determined geometrically by methods such as parallaxan apparent change in the position of an object that occurs with a change in perspective. Access to the space telescope may be limited, but you can reproduce parallax yourself by holding a finger at arm’s length and watching it seemingly change position in close one eye then the other.
As a result, the researchers used several anchor points in the local universe, including the galaxy NGC 4258, located more than 20 million light years away; the Magellanic Clouds, which are a pair of dwarf galaxies located about 200,000 light years away; and numerous variable stars within the Milky Way.
Then they included a multitude of objects at measured distances, including old, dying red giant stars and “megamasers“, the intensely bright cosmic lasers generated in the accretion disks of supermassive black holes.
The researchers also included more than 7,500 galaxies, observed by facilities such as the Hubble Space Telescope and the Dark energy spectroscopic instrumentat a distance of more than a billion light years.
As a result, the local remote network developed in this study represents the most precise direct measurement of the Hubble constant in the local universe: 73.50 kilometers per second per megaparsec, with a relative uncertainty of 1.09%. The conclusion? The Hubble voltage is real, similar to previously measured values, and not just an artifact.
The fact that this discrepancy persists could suggest that measurements of the early universes need to be similarly re-evaluated at a deeper level.
“An interesting idea, relatively new and perhaps more natural, involves primordial magnetic fields, which could change the scale of the structure observed in the CMB,” study co-author John Blakesleedirector of research and scientific services at NOIRLab, explained via email.
Excitingly, this research supports the idea that new physics is needed to illuminate dark energy and other driving forces of expansion and ultimate destiny of the universe. And because this framework is modular, upcoming methods and data from next-generation observatories could finally resolve the Hubble tension – but then again, that’s what cosmologists have been hoping for for more than a decade.
Casertano, S., Anand, G., Anderson, RI, Beaton, R., Bhardwaj, A., Blakeslee, JP, Boubel, P., Breuval, L., Brout, D., Cantiello, M., Reyes, MC, Csörnyei, G., De Jaeger, T., Dhawan, S., Di Valentino, E., Galbany, L., Gil-Marín, H., Graczyk, D., Huang, C., . . . Note, A. (2026). The Remote LAN: A Community Consensus Report on Measuring the Hubble Constant with Approximately 1% Accuracy Astronomy and Astrophysics708, A166. https://doi.org/10.1051/0004-6361/202557993
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