Redshift-dependent redshift (z(z))

Ascertain whether the cosmological redshift variable z may itself depend on redshift, i.e., take the self-referential form z(z) (including iterated forms such as z(z(z)) and z(z(z(z)))), and characterize the implications of such a dependence for cosmological inference.

Background

Beyond varying constants, the authors point to the possibility that redshift itself could be redshift-dependent, introducing a self-referential structure to z that would have broad implications for cosmological measurements and tensions.

This explicit uncertainty highlights a foundational question about the definition and behavior of redshift, proposed for investigation in a separate paper, and suggests potentially far-reaching consequences for cosmological modeling.