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→Non-equilibrium states
For purposes of physical analysis, it is often enough convenient to make an assumption of thermodynamic equilibrium. Such an assumption may rely on trial and error for its justification. If the assumption is justified, it can often be very valuable and useful because it makes available the theory of thermodynamics. Elements of the equilibrium assumption are that a system is observed to be unchanging over an indefinitely long time, and that there are so many particles in a system, that its particulate nature can be entirely ignored. Under such an equilibrium assumption, in general, there are no macroscopically detectable fluctuations. There is an exception, the case of critical states, which exhibit to the naked eye the phenomenon of critical opalescence. For laboratory studies of critical states, exceptionally long observation times are needed.
For purposes of physical analysis, it is often enough convenient to make an assumption of thermodynamic equilibrium. Such an assumption may rely on trial and error for its justification. If the assumption is justified, it can often be very valuable and useful because it makes available the theory of thermodynamics. Elements of the equilibrium assumption are that a system is observed to be unchanging over an indefinitely long time, and that there are so many particles in a system, that its particulate nature can be entirely ignored. Under such an equilibrium assumption, in general, there are no macroscopically detectable fluctuations. There is an exception, the case of critical states, which exhibit to the naked eye the phenomenon of critical opalescence. For laboratory studies of critical states, exceptionally long observation times are needed.
为了进行物理分析，通常假设热力学平衡就足以方便。 这样的假设可能依赖于反复试验和试错来证明其合理性。 如果假设是合理的，那么它通常会非常有价值，因为它使热力学理论成为可能。 平衡假设的要素是，观察到的系统会无限期地保持不变，并且因为系统中有很多粒子，以至于完全可以忽略其微粒性质。 通常，在这种平衡假设下，没有宏观上可检测到的波动。 临界状态是一个例外，它以肉眼显示出临界乳光现象。 对于临界状态的实验室研究，需要非常长的观察时间。