Maxwell Demon is the ideal model of james maxwell's fictional existence. Maxwell imagined that a container was divided into two parts, A and B. A and B contained the same gas at the same temperature. Maxwell demon guards the "secret door" between these two parts, and can observe the speed of molecular movement, so that the molecules with faster molecular movement flow to one part and the slower molecules flow to the other part. After a long time, the average speed of the two parts of the molecule, that is, the temperature (refer to the microscopic explanation of temperature in statistical mechanics), has a difference and is getting bigger and bigger. It can be concluded that this process is an entropy reduction process, and the existence of Maxwell's demon makes this process spontaneous, which obviously violates the second law of thermodynamics.

Leo Szilard put forward one of the most famous answers in 1929. Szilard pointed out that if Maxwell Demon really exists, the process of observing molecular speed and obtaining information will inevitably produce extra energy consumption and entropy. Loschmidt's paradox, also known as reversibility paradox, points out that if microscopic particles are reversed according to the dynamic law with time reversibility, the system will produce the result of entropy decrease, which obviously goes against the principle of entropy increase.

In view of this paradox, Boltzmann put forward that the process of entropy increase is not monotonous, but for a macro system, the probability of entropy increase is much greater than that of entropy decrease; Even when thermal equilibrium is reached, entropy will fluctuate around its maximum value, and the greater the amplitude, the smaller the probability of fluctuation. Some existing experimental results are basically consistent with Boltzmann's account.

The second law of thermodynamics is based on the observation and summary of experimental results. Although no experimental phenomenon contrary to the second law has been found in the past 100 years, it is still impossible to strictly prove the correctness of the second law in theory. Since 1993, Denis J.Evans and other scholars have questioned the second law of thermodynamics in theory and published some theories about "entropy fluctuation" from the perspective of statistical thermodynamics, such as the more important FT theory. Subsequently, in 2002, G.M.Wang et al. published an article entitled "Experimental Proof of Small Systems Violating the Second Law of Thermodynamics in a Short Time" in Physical Review Letters. From the point of view of experimental observation, it is proved that the spontaneous entropy reduction reaction of thermal system and isolated system is the possible main item under certain conditions: Gibbs paradox

Boltzmann relation gives a representation of entropy, which is not extended. This leads to a conclusion that obviously violates the second law of thermodynamics, Gibbs paradox, which allows the entropy of a closed system to decrease. In the usual explanation, the indiscernibility of particles in quantum mechanics is cited to explain that the properties of particles in the system do not affect the entropy of the system, so as to avoid this paradox. However, now more and more papers adopt the view that the change of entropy explanation can just ignore the influence of the change of molecular arrangement. However, the existing Sackur-Tetrode equation is an extension of the explanation of ideal gas entropy. See also: Heat Death Theory.

The theory of thermal death is a theory that extends the second law of thermodynamics to the whole universe. The energy of the universe is constant, and the entropy of the universe will tend to be maximum. With this process, the ability of the universe to further change is getting smaller and smaller, and various movements such as machinery, physics, chemistry and life are gradually transformed into thermal movements, and finally the thermal equilibrium state with equal temperatures everywhere is reached. At this time, nothing will change, and the universe is in a dead and eternal state. The theory of cosmic thermal silence is only a possible guess.

If the first and second laws of thermodynamics are applied to the universe, a typical isolated system, we will get the following conclusion: 1. The energy of the universe is conserved, 2. The entropy of the universe will not decrease. Then we will get that the entropy of the universe will eventually reach the maximum, that is, the universe will eventually reach thermal equilibrium, which is called thermal silence.

/kloc-in the 0/9th century, there were two more influential refutations to the theory of heat death. One is the "wave theory" put forward by Boltzmann (1872), and the other is Engels' refutation with immortal movement in Dialectics of Nature (1876). Today's understanding of the universe (1. The universe is expanding; 2. As a self-gravitation system, the universe is an unstable system with negative heat capacity. It is pointed out that the universe is an unstable thermodynamic system, and it does not exist in the equilibrium state envisaged by the static universe model, so its entropy has no maximum, that is, thermal silence does not exist.