Studying the Behavior of Radial Free Geodesics in ΛCDM Model

This paper presents an analytical study of the behavior of radial free-geodesics in the Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime within the Lambda Cold Dark Matter (ΛCDM) model. Using the radial free motion solutions, we provide two methods for characterizing the geodesics and defines a general formula that encapsulates all possible solutions, determined by two initial conditions. We show that the past light cone, event horizon, and particle horizon, can be considered as special cases of this overarching formula. Furthermore, the paper explores the free geodesics within the currently accepted cosmological model based on the recent Planck results, thoroughly examining the various possible geodesic scenarios.