ints." Such a path is called a geodistic . Thus, for a black hole in general relativity, a light beam originating on the surface that cannot escape really travels nowhere. In some sense, all "surface" points can be viewed as the same point and the object can be said to have been sealed off from the ordinary space and time of outside observers. The point from which light can no longer escape is known as the event horizon since knowledge of events beyond that point can never be transmitted to the outside world by a light beam or any other mechanism. The event horizon imposes a form of censorship on the makeup of a black hole. Indeed, the only aspects of a black hole that may be ascertained from outside are its mass, net charge, and rate of spin. No internal processes that depend on time in any way can be detected in the external environment, for that would constitute sending signals from inside the black hole to the outside when not even light can escape. This "censorship" is what is responsible for the small number of measurable properties of the black hole itself-mass, spin, and charge.
             While there are complications in defining the size of a black hole, one can uniquely specify its circumference and thus define a radius as just the circumferenc
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