Redshift Drift Null Prediction

A striking implication of the standard ΛCDM cosmology is that the redshift drift signal should be negative at low redshifts (z ≲ 1.9) — sources at these redshifts should drift to lower redshift over time as the universe's accelerating expansion decelerates the apparent recession — and positive at higher redshifts (z ≳ 1.9), where the matter-dominated decelerating expansion dominated in the past. The sign change at z ~ 1.9 is a precise, unambiguous prediction of the standard concordance model that depends only on the values of Ω_m and Ω_Λ, not on H₀ or other parameters. Any future detection of a sign reversal at a different redshift, or a failure to detect the sign change, would fundamentally rule out or strongly modify ΛCDM's energy content description. This prediction is a high-value target for the ACES ELT program precisely because of its clean diagnostic power.

Successive Collision Theory predicts a drift sign-change at a redshift that differs modestly but detectably from the ΛCDM value of z ~ 1.9. In SCT, the effective cosmological term Λ_eff(t) was smaller in the past (less tensor mesh has dissipated at earlier epochs) and grows toward the present. The expansion history H(z) therefore departed from the ΛCDM constant-Λ trajectory at a rate determined by the mesh dissipation timeline. The redshift at which dz/dt = 0 — the drift null — moves to a slightly higher value in SCT compared to ΛCDM, because the effective dark energy density at intermediate redshifts was lower than ΛCDM's constant Λ and the matter-to-acceleration crossover epoch is shifted. The predicted shift is at the level of Δz ~ 0.1–0.2 in the drift null location, potentially detectable with a sufficiently dense quasar monitoring sample at z ~ 1.7–2.1.

The precise location of the drift null carries additional SCT information through the hereditary time transmission mechanism. The null occurs at the redshift where the deceleration from matter dominance exactly cancels the acceleration from Λ_eff; since Λ_eff itself depends on the depth of the observer's embedding in the frame hierarchy, the null redshift as measured by an embedded observer within the KBC supervoid differs slightly from that measured by a hypothetical observer at the cosmic mean density. The void environment elevates the observer's Λ_eff, pulling the null to slightly higher redshift relative to the global mean. SCT therefore predicts a mild directional dependence of the null location correlated with the large-scale density field: lines of sight through denser regions will show the null at slightly lower redshift than lines of sight through the void core. This angular variation of the drift null location is a uniquely clean signature of the spatial Λ_eff gradient.