Abstract
In this study, we investigate foliations of the Schwarzschild and Reissner–Nordstr¨om spacetimes.
In particular, we construct flat spacelike hypersurfaces by reducing the four-dimensional
spacetime using spherically symmetric time functions of the form t = F(r). These functions
are determined by imposing the condition that the induced three-dimensional metric be Riemann
flat. The resulting family of solutions is then visualised using Carter–Penrose diagrams.