Can Entropy and the Second Law be Applied to the Entire Universe?

Dear Colleagues,

The aim of this special issue of Entropy is to discuss and provide answers to the two questions posed in the title. Clausius, who introduced the concept of entropy, also formulated the Second Law:

“The Entropy of the Universe always increases”

Ever since Clausius made this statement people have discussed the concept of entropy and the Second Law in connection with the entire universe.  Many popular science books show graphs of the “Entropy of the Universe” in the past and in the future. Some even discuss the value of the entropy of the universe at the Big-Bang. On the other hand, many textbooks would tell you that since entropy always increases, the universe will come to a “Thermal death” in the far future.

There are essentially two distinguishable questions: The first, concerns the possibility of defining entropy, and the second, concerns the applicability of the Second Law to the entire universe. Most writers on thermodynamics intertwine these two questions. In fact, most people define the Second Law as “the law of increasing entropy.” In fact one can define, interpret, and apply the concept of entropy without ever mentioning the Second Law. By the same token, one can also formulate, interpret and apply the Second Law without mentioning the concept of entropy.

Thus we pose two fundamental questions for this special issue:

Can entropy be defined in a consistent way for the entire universe?

Can one show that the Second Law is applicable to the entire universe?

Prof. Dr. Arieh Ben-Naim
Guest Editor

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