The behaviour of the universe on the largest scales is being examined through weak gravitational lensing, a method that may confirm or challenge the long-standing Cosmological Principle. This principle, which asserts that the universe is both homogeneous and isotropic, underpins the Standard Model of Cosmology. If inconsistencies are detected, fundamental assumptions about the universe’s structure may need to be reconsidered. Observations from new space telescopes are being used to analyse potential deviations, with findings expected to provide deeper insights into cosmic evolution.

Cosmological Principle Under Investigation

According to a study published in the Journal of Cosmology and Astroparticle Physics (JCAP), a methodology has been proposed to test the universe’s isotropy using weak gravitational lensing data. This effect, predicted by general relativity, occurs when light from distant galaxies is subtly bent by massive cosmic structures. Researchers have suggested that anomalies in this lensing data may indicate deviations from the assumption that the universe has no preferred direction.

James Adam, an astrophysicist at the University of the Western Cape, Cape Town, and lead author of the study, told Phys.org that the principle suggests no true centre exists in the universe. The Standard Model of Cosmology, which relies on this assumption, has been supported by various observations. However, inconsistencies in cosmic expansion measurements and the cosmic microwave background have raised questions about possible anisotropies.

Observations from the Euclid Space Telescope, launched in 2023, are being analysed to detect possible anisotropies. Weak gravitational lensing alters galaxy shapes in a measurable way, allowing researchers to distinguish between two lensing components—E-mode and B-mode shear. In an isotropic universe, only E-modes should appear on large scales, while B-modes remain weak. A correlation between the two could indicate a non-uniform cosmic expansion.

Future Observations and Potential Impact

The study simulated how an anisotropic expansion would modify weak lensing signals, demonstrating that Euclid’s data could be used to detect such deviations. If verified, these findings could require adjustments to current cosmological models. Adam stated to Phys.org that extensive validation is necessary before any fundamental assumptions are reconsidered. Future telescopic data will be analysed to confirm whether these anomalies represent real physical phenomena or observational errors.