A new, independent measurement has solidified the growing evidence that the Universe is expanding faster than predicted by our current understanding of physics, deepening the so-called “Hubble tension.” Led by Dan Scolnic at Duke University, the research, published in the Astrophysical Journal Letters, provides the strongest support yet for a faster-than-expected expansion rate.
“The tension now turns into a crisis,” stated Scolnic, emphasizing the significant discrepancy between observed data and theoretical models.
Determining the Universe’s expansion rate – the Hubble constant – has been a cornerstone of cosmology since Edwin Hubble’s groundbreaking discovery in 1929. Scolnic likens this pursuit to constructing the Universe’s growth chart: we know its initial size at the Big Bang, but how did it reach its current dimensions?
The “baby picture” represents the distant Universe, the primordial seeds of galaxies, while the “current headshot” depicts the local Universe, encompassing our Milky Way and neighboring galaxies. The standard cosmological model aims to connect these two snapshots with a growth curve. However, this model is failing to accurately depict the observed expansion rate.
“This is essentially saying that our model of cosmology might be fundamentally flawed,” Scolnic explained.
Precisely measuring the Universe’s expansion requires a cosmic distance ladder, a series of interconnected methods for determining distances to celestial objects. Scolnic’s team utilized a ladder constructed by the Dark Energy Spectroscopic Instrument (DESI) collaboration, which observes over 100,000 galaxies nightly.
Recognizing the need for a more accurate anchor point closer to Earth, Scolnic focused on refining the distance to the Coma Cluster, a nearby galaxy cluster. “The DESI collaboration built a robust ladder, but it lacked a precise first rung,” said Scolnic. “I knew how to obtain that crucial rung, and I understood the significant impact it would have on our understanding of the Hubble constant.”
To determine the precise distance to the Coma Cluster, the team meticulously analyzed the light curves of 12 Type Ia supernovae within the cluster. These supernovae serve as reliable “standard candles” due to their predictable luminosity, enabling accurate distance calculations.
The team arrived at a distance of approximately 320 million light-years, falling squarely within the range of distances reported by previous studies over the past four decades, a strong indicator of its accuracy.
“This measurement is unbiased by any preconceived notions about the outcome of the Hubble tension,” emphasized Scolnic. “The Coma Cluster is a relatively nearby object, and its distance has been studied extensively long before the significance of the Hubble tension was fully recognized.”
Using this high-precision measurement as the foundation, the team calibrated the remaining rungs of the cosmic distance ladder. Their analysis yielded a Hubble constant value of 76.5 kilometers per second per megaparsec, indicating that the local Universe is expanding 76.5 kilometers per second faster for every 3.26 million light-years.
This value aligns with other recent measurements of the local Universe’s expansion rate. However, it remains in stark contrast to predictions derived from observations of the distant Universe. The fundamental question remains: is the discrepancy due to flaws in our measurements or in our cosmological models?
Scolnic’s team’s new results strongly suggest that the root of the Hubble tension lies within the limitations of our current cosmological models.
“Over the past decade, numerous re-analyses have been conducted by the scientific community to scrutinize the validity of our original findings,” stated Scolnic, whose research has consistently challenged the Hubble constant predicted by the standard model of physics. “Despite significant variations in the specific methodologies employed, we consistently arrive at very similar results. This provides compelling evidence for the robustness of our findings.”
“We are now at a critical juncture where we are rigorously testing the cosmological models that have served us well for the past two and a half decades, and we are encountering discrepancies,” said Scolnic. “This may necessitate a fundamental re-evaluation of our understanding of the Universe. It’s an exciting time for cosmology, as it highlights that there are still profound mysteries awaiting discovery.”
Reference: Scolnic, D., Riess, A.G., Murakami, Y.S., Peterson, E.R., Brout, D., Acevedo, M., Carreres, B., Jones, D.O., Said, K., Howlett, C. and Anand, G.S., 2025. The Hubble Tension in our own Backyard: DESI and the Nearness of the Coma Cluster. The Astrophysical Journal Letters, 979, L9. DOI: 10.3847/2041-8213/ada0bd
