Stacking Voids (Cold Bias)

When large cosmic voids are stacked in CMB temperature maps, the expected integrated Sachs-Wolfe signal — a subtle warming from photons falling into and climbing out of evolving potential wells — consistently shows a cold bias: the stacked signal is colder than ΛCDM predicts for the observed void population. This cold bias is statistically significant and has been confirmed with multiple void catalogs and CMB datasets. Successive Collision Theory resolves this through two reinforcing effects. First, the SCT dynamical effective cosmological term is enhanced inside underdense regions relative to the ΛCDM constant Λ value. This means the gravitational potential well of a void is dissipating faster in SCT than in ΛCDM, and photons traversing the void gain less energy from falling into the potential than they lose by climbing out of a shallower well — producing a net cold effect larger than the standard integrated Sachs-Wolfe calculation.

Second, collision-pocket voids have a different internal density profile from gravitationally evolved ΛCDM voids. Their interiors are more uniformly empty — swept cleaner — and their walls are sharper and more overdense. The steeper density contrast at the void boundary means the potential gradient is sharper and the photon traversal path encounters a more abrupt transition from underdense to overdense. This asymmetric entry and exit from a sharper-walled void produces a different temperature signal geometry than ΛCDM's smooth void profiles predict, contributing additional cold bias when stacked. The stacking cold bias is therefore a composite of the enhanced dynamical Λ_eff inside voids and the sharper, deeper void profiles produced by collision-front sweeping, both of which are direct predictions of SCT that distinguish it from the standard model.