 The global and geometrical nature of black holes also raises interesting questions about the sense in which one may or should think of them as physical objects or systems (Curiel 2019). A black hole is simply a geometrically characterized surface in spacetime, with no ordinary matter at the event horizon, and no other local feature that would allow one to detect it. The same questions as with singularities  (section 2.1),  therefore, force themselves on us here: in what sense, if any, should we attribute existence to black holes, in so far as, considered locally, they are an undistinguished region of spacetime whose physically important properties manifest only as global structure? 