While this research doesn't definitively resolve all questions about cosmic expansion, it offers a compelling alternative to dark energy that aligns with both Einstein's general relativity and our observations of the universe's structure. As more data becomes available from new telescopes and surveys, we may find that the greatest mystery in modern cosmology isn't why the universe's expansion is accelerating, but rather how our perception of time and space across cosmic scales affects our measurements of that expansion.
The research team analyzed the Pantheon+ catalogue, which contains 1,690 supernova observations representing 1,535 unique supernovae. They developed a new statistical framework that specifically avoided assumptions tied to the standard Lambda Cold Dark Matter (ΛCDM) model. A key innovation was their treatment of the data covariance matrix - they reconstructed it to be as independent as possible from cosmological model assumptions, particularly those related to peculiar velocities. This allowed for a fairer comparison between timescape cosmology and the standard model. The team also introduced new statistical methods to refine Type Ia supernova light-curve analysis, focusing particularly on parameters that influence brightness measurements.
The analysis revealed several key findings. The team identified a "scale of statistical homogeneity" at a redshift of 0.075, significantly larger than previous estimates. In analyzing the Bayesian evidence, they found that timescape cosmology provided a better overall fit to the data than ΛCDM for certain subsamples of the data. Importantly, when examining data beyond this homogeneity scale, the results showed consistent patterns that aligned with timescape predictions. The study found varying levels of statistical support for timescape depending on which subset of the data was analyzed, with some subsets showing strong evidence in favor of timescape while others showed more modest support.
First, the analysis couldn't include certain bias corrections typically used in supernova studies, as these corrections assume a standard ΛCDM framework. The team also had to exclude 15 supernovae from their analysis due to statistical constraints. Additionally, the study noted that their findings with the full sample showed different results from smaller subsamples, suggesting possible selection effects that need further investigation. The research also acknowledges that while their results challenge the need for dark energy, they don't definitively rule it out.
The study suggests a potential paradigm shift in how we understand cosmic expansion. Rather than requiring mysterious dark energy, observed acceleration might result from how we measure cosmic distances and time across vastly different regions of space. The research provides a possible resolution to the Hubble tension and other cosmological puzzles. However, the team emphasizes that definitive confirmation will require additional data from upcoming surveys. Their work also highlights the importance of examining fundamental assumptions in cosmological models, particularly regarding how we average over cosmic structures.
The research was supported by the Marsden Fund administered by the Royal Society of New Zealand, Te Aparangi, under grants M1271 and M1255. Additional support came from the Rutherford Foundation Postdoctoral Fellowship and the German Academic Exchange Service. The researchers declared no competing interests. The study benefited from collaboration with the Pantheon+ team, who provided essential data and feedback on implementation details.