![]() ![]() Hence it makes sense to attribute entropy to a black hole. In ordinary physics entropy is a measure of missing information. Thus a black hole can be said to hide information. By blocking all signal travel through it, the event horizon prevents an external observer from receiving information about the black hole (save for the mentioned few parameters see Figure 2).Thus by analogy one needs to associate entropy with a black hole. Thermodynamic entropy quantifies the said multiplicity. In thermodynamics one meets a similar situation: many internal microstates of a system are all compatible with the one observed (macro)state. Thus there are many possible internal states corresponding to that black hole. For any specific choice of these parameters one can imagine many scenarios for the black hole's formation. A stationary black hole is parametrized by just a few numbers (Ruffini and Wheeler 1971): its mass, electric charge and angular momentum (and magnetic monopole charge, except its actual existence in nature has not been demonstrated yet).Associating entropy with the black hole provides a handle on the thermodynamics. Thus a thermodynamic description of the collapse from that observer's viewpoint cannot be based on the entropy of that matter or radiation because these are unobservable. However, the hole's interior and contents are veiled to an exterior observer. ![]() A black hole is usually formed from the collapse of a quantity of matter or radiation, both of which carry entropy.There are several ways to justify the concept of black hole entropy (Bekenstein 1972, 1973). Is it meaningful or desirable to associate entropy with it ? Is this possible at all ? Only the hole's mass \(M\ ,\) angular momentum \(J\) and electric charge \(Q\) are sensed by an exterior observer.Ī black hole may be described as a blemish in spacetime, or a locale of very high curvature. Figure 2: Due to the disposition of the local light cone, the event horizon stops any signals bearing interior information from exiting the black hole. ![]()
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