ENTROPY

ENTROPY, a concept introduced in thermodynamics and serving as a measure of the irreversibility of a process, a measure of the transition of energy into a form from which it cannot spontaneously pass into other forms. All conceivable processes occurring in any system can be divided into two groups: reversible processes, which can proceed equally well in either direction, and irreversible processes, which can occur only in one direction and cannot proceed in reverse. If we perform any reversible process in one direction, and then, reversing it, perform it in the opposite direction, then, returning to the starting point, we will have no changes either in the system itself that participated in the process, or in the surrounding space, and we will return exactly to the original position as if the process had not been performed at all. Reversible processes can include, for example, all purely mechanical movements without friction forces. Irreversible processes include all real processes. If we take, for example, the same purely mechanical movements, but taking into account friction forces, which always actually exist, then the mechanical energy of motion will be partially expended on friction, turning into heat. When reversing the motion, however, we can no longer obtain mechanical energy from this heat and thus cannot return to the original position without introducing any changes into the surrounding space. In reversible processes, the amount of E. (of the system) does not change, in irreversible processes it increases. From the point of view of the molecular-kinetic theory of matter, E. represents a measure of the probability of a given state of the system being realized, namely E. is proportional to the logarithm of the probability of the given state. In all natural processes, the system always transitions from less probable states to more probable states, and consequently the amount of E. will increase in this process. Let us suppose, for example, we have a system consisting of two bodies, one of which is at a higher temperature, the other at a lower one. In their interaction, the transfer of thermal energy can occur only in one direction—from the warmer body to the colder one. In such a transition, the entropy S, equal to the amount ~, where Q is the amount of heat, and T is the absolute temperature, will change by the amount ΔS = ΔS₁ + ΔS₂, where ΔS₁ and ΔS₂ are the changes in E. of the warmer and colder bodies. But ΔS₁ = ---, and ΔS₂ = ^~, where ΔQ is the amount of heat transferred from the first body to the second, and T₁ and T₂ are the temperatures of these bodies. Since by condition T₁ > T₂, then ΔS = -ΔQ/T₁ + ΔQ/T₂ > 0, i.e., the increment of E. is positive, or in other words, E. increases. The reverse transfer of heat from a colder body to a warmer one is impossible without any external influences. Such a transfer would correspond to a decrease in E. Thus we come to the conclusion that the E. of a closed system can only increase. This position, known under the name of the 'second law of thermodynamics,' led a number of scientists with an idealistic worldview (for example, Clausius) to a certain theory of the 'heat death of the universe.' Due to the dissipation of energy (see), all forms of energy must eventually pass into heat, which will be uniformly distributed throughout the universe. At this point, all processes must cease, since they all involve transitions of energy from one form to another, which in this case become impossible, and consequently universal death, from which there is no escape, sets in. However, this theory, which inevitably leads to the idea of the beginning and end of the world, and hence its 'creation' and so on, was exhaustively criticized by Engels on the basis of a materialistic worldview. Boltzmann, based on a statistical consideration of E., arrives at the same conclusions as Engels. The essence of these conclusions is as follows. The law of increasing E. has only a statistical (and not absolute) character, i.e., those processes are most probable in which E. increases, however, processes that proceed with a decrease in E. can occur, although with a small probability (and thus rarely). It is these very rare deviations from the 2nd law of thermodynamics that give rise to a new world from the state of heat death to which the entire universe must inevitably come, according to Clausius, as a result of the dissipation of energy. These deviations from our human point of view will occur extremely rarely, however, from a cosmic point of view, compared to the existence time of the universe, they will still be frequent enough. This theory received direct experimental confirmation in the works of Smoluchowski in the analysis of Brownian motion and must at present be considered the only one correctly reflecting reality.

G. Neuymin.