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→Gravitational systems
==Gravitational systems==
==Gravitational systems==
==Gravitational systems==
== Gravitational systems 重力系统 ==
In systems that do not require for their descriptions the general theory of relativity, bodies always have positive [[heat capacity]], meaning that the temperature rises with energy. Therefore, when energy flows from a high-temperature object to a low-temperature object, the source temperature is decreased while the sink temperature is increased; hence temperature differences tend to diminish over time. This is not always the case for systems in which the gravitational force is important and the general theory of relativity is required. Such systems can spontaneously change towards uneven spread of mass and energy. This applies to the universe in large scale, and consequently it may be difficult or impossible to apply the second law to it.<ref name="Grandy 151">Grandy, W.T. (Jr) (2008), p. 151.</ref> Beyond this, the thermodynamics of systems described by the general theory of relativity is beyond the scope of the present article.
In systems that do not require for their descriptions the general theory of relativity, bodies always have positive [[heat capacity]], meaning that the temperature rises with energy. Therefore, when energy flows from a high-temperature object to a low-temperature object, the source temperature is decreased while the sink temperature is increased; hence temperature differences tend to diminish over time. This is not always the case for systems in which the gravitational force is important and the general theory of relativity is required. Such systems can spontaneously change towards uneven spread of mass and energy. This applies to the universe in large scale, and consequently it may be difficult or impossible to apply the second law to it.<ref name="Grandy 151">Grandy, W.T. (Jr) (2008), p. 151.</ref> Beyond this, the thermodynamics of systems described by the general theory of relativity is beyond the scope of the present article.