Telescopes' Final Data Release Challenges Cosmological Theories

The Atacama Cosmology Telescope, located in Chile, has released its final data after nearly two decades of operation, and this data is causing significant upheaval in the cosmological community. A study published in the Journal of Cosmology and Astroparticle Physics utilized this data to assess about thirty extended models of the universe's evolution, which are alternatives to the standard model of cosmology.

Researchers found that all the extended models they tested were ruled out, which was a surprising outcome, as stated by Erminia Calabrese, a cosmologist at Cardiff University and co-author of the study.

The study was conducted independently, aiming to evaluate these models without bias, and the results indicate that the new observations in polarization and at new scales have limited the theoretical possibilities for explaining the universe's expansion.

This situation highlights a deepening cosmological mystery, particularly concerning the Hubble tension, which refers to the discrepancy in measurements of the universe's expansion rate. There are two primary methods to measure the Hubble constant: one involves examining the cosmic microwave background radiation, while the other focuses on local observations of galaxies and supernovae.

According to the standard model of cosmology, both methods should yield the same value, but they do not, creating the Hubble tension. The ACT data further strengthens the case for this discrepancy, as it confirms the Hubble tension with unprecedented precision.

The telescope's observations provided detailed polarization maps of the cosmic microwave background, enhancing previous temperature maps produced by the European Space Agency's Planck spacecraft. Due to ACT's larger primary mirror, measuring approximately twenty feet in diameter, its maps offer much higher resolution than those from Planck.

Colin Hill, a cosmologist at Columbia University and co-author of the study, noted that the ACT data fills critical gaps in understanding the cosmic microwave background and that the Hubble constant inferred from ACT data aligns with that from Planck, solidifying the Hubble tension.

While ruling out many extended models narrows the range of theoretical possibilities, it also provides a clearer path for future research. The final release of ACT data marks a new beginning for cosmologists as they continue to seek answers to resolve the Hubble tension, indicating that while the telescope's operational phase has ended, its contributions to the field will persist for years to come.