New test to confront fundamental cosmological assumptions

Researchers are delving into a "time dilation dipole" to evaluate the cosmological principle, scrutinizing its detectability in extensive cosmological source surveys. Drs. Lewis and Oayda aim to provide a new assessment and address inconsistencies in dipole measurements from other observations.

In a recent scientific endeavor, researchers from the Sydney Institute for Astronomy, School of Physics in Australia, have embarked on a unique test of the cosmological principle. This foundational concept in modern cosmology posits that the universe should exhibit homogeneity and isotropy on large scales, especially for observers moving with the Hubble flow. This principle forms the foundation for the widely accepted Friedmann-Lemaître-Robertson-Walker metric within the ΛCDM paradigm. However, this study probes the cosmological principle by analyzing the observed dipole imprinted on the Cosmic Microwave Background (CMB), interpreting it as an indication of deviation from the Hubble flow. Such deviation introduces a discernible, directionally dependent time dilation across the celestial sphere, which could yield novel insights.

In their exploration of this phenomenon, Lewis and Oayda outline the potential for detecting this 'time dilation dipole.' They provide an overview of practical steps involved in extracting this phenomenon from extensive catalogues of cosmological sources such as quasars and supernovae, each characterized by intrinsic timescales. Despite its relatively modest scale - approximately 0.1% - they suggest its potential detectability in comprehensive surveys of variable cosmological sources. To enhance understanding, they plan to analyze alignment between this time dilation dipole and kinematic dipole derived from CMB data, offering a fresh perspective on the cosmological principle while addressing disparities noted in other observational studies.

This investigation contributes to ongoing discourse in cosmology by potentially refining our fundamental assumptions about universe's structure and behavior. As scientists delve deeper into cosmic phenomena, their findings may pave the way for a more nuanced understanding of the cosmos and its underlying principles.

Oxford Academic: Oliver T. Oayda, Geraint F. Lewis. Testing the Cosmological Principle: On the Time Dilation of Distant Sources, Monthly Notices of the Royal Astronomical Society (May 2023). DOI: doi.org/10.48550/arXiv.2305.06771