We discuss the tension between the possible existence of Painleve-Gullstrand
    coordinate systems versus the explicit geometrical features of the Kerr
    spacetime; a subject of interest to Professor Thanu Padmanabhan in the weeks
    immediately preceding his unexpected death. We shall carefully distinguish
    strong and weak Painleve-Gullstrand coordinate systems, and conformal variants
    thereof, cataloguing what we know can and cannot be done — sometimes we can
    make explicit global statements, sometimes we must resort to implicit local
    statements. For the Kerr spacetime the best that seems to be achievable is to
    set the lapse function to unity and represent the spatial slices with a
    3-metric in factorized unimodular form; this arises from considering the Doran
    version of Kerr spacetime in Cartesian coordinates. We finish by exploring the
    (limited) extent to which this construction might possibly lead to implementing
    an “analogue spacetime” model suitable for laboratory simulations of the Kerr

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