P13: Weak Gravitational Lensing and the S8 Tension in BFUT: Why Late-Time Clustering Inference Is Not a Unique Test of Lambda-CDM
Year: 2026
Type: conference-abstract
Abstract: Weak gravitational lensing surveys - including KiDS, DES, and HSC - consistently measure a lower amplitude of matter fluctuations, parametrised by S8, than the value predicted by extrapolating the Planck CMB best-fit Lambda-CDM cosmology forward to the present epoch. This S8 tension is consistently measured at 2 to 3 σ significance across multiple independent surveys using different instruments, analysis pipelines, and sky regions, with some combined analyses reporting higher significance. Lambda-CDM treats this as an unexplained internal inconsistency requiring new physics, additional free parameters, or systematic uncertainties in the lensing analyses. A particularly important empirical pattern is that the low-S8 preference is strongest in low-redshift optical weak-lensing surveys, while higher-redshift CMB lensing measurements are generally closer to the Planck expectation. This pattern is consistent with a discrepancy concentrated in the late-time growth regime and motivates the redshift-dependent BFUT mechanism tested in Section 5. Importantly, the widely cited S8 value is not a direct observable but a compressed parameter inferred from shear correlations under specific modelling assumptions. The qualitative low-S8 trend across surveys may therefore be robust even when the exact numerical precision of the inferred value is less stable than often presented. This paper examines the S8 tension from within the Big Flare-Up Theory framework [9]. BFUT proposes that the universe is infinite, non-expanding, and dynamically organised through gravitational sorting over indefinitely long timescales. Within BFUT, the apparent discrepancy between CMB-inferred and lensing-inferred structure amplitudes is interpreted as a consequence of an ongoing, dynamically active cosmic web whose present-epoch clumpiness need not match the extrapolation of early-universe conditions through a finite-age expanding-universe model. The Planck CMB, SZ cluster abundance, and CMB-lensing measurements provide different observational constraints that are not fully reconciled by a single standard growth-history interpretation. BFUT's living-universe picture provides an alternative interpretation in which structure continues to evolve through gravitational assembly, rotation, and matter cycling.
Author: Sharma, Vijay Shankar
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7148589090
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