Irreversible process

All complex natural processes are irreversible,[1][2][3][4] although a phase transition at the coexistence temperature (e.g. melting of ice cubes in water) is well approximated as reversible.

Then dissipation would occur; the temperature distribution would become uniform with no work being done, and this would be irreversible because you couldn't add or remove heat or change the volume to return the system to its initial state.

As another example, to approximate the expansion in an internal combustion engine as reversible, we would be assuming that the temperature and pressure uniformly change throughout the volume after the spark.

One of the reasons that Diesel engines are able to attain higher efficiency is that the combustion is much more uniform, so less energy is lost to dissipation and the process is closer to reversible.

While the fundamental theoretical laws of physics are all time-reversible,[8] experimentally the probability of real reversibility is low and the former state of system and surroundings is recovered only to certain extent (see: uncertainty principle).

The German physicist Rudolf Clausius, in the 1850s, was the first to mathematically quantify the discovery of irreversibility in nature through his introduction of the concept of entropy.

This paradox clearly taints microscopic explanations of macroscopic tendency towards equilibrium, such as James Clerk Maxwell's 1860 argument that molecular collisions entail an equalization of temperatures of mixed gases.

Nevertheless, the principle of dissipation of energy is compatible with a molecular theory in which each particle is subject to the laws of abstract dynamics.Another explanation of irreversible systems was presented by French mathematician Henri Poincaré.

Applying chaos theory to the second law of thermodynamics, the paradox of irreversibility can be explained in the errors associated with scaling from microstates to macrostates and the degrees of freedom used when making experimental observations.

Sensitivity to initial conditions relating to the system and its environment at the microstate compounds into an exhibition of irreversible characteristics within the observable, physical realm.

According to the biologists Humberto Maturana and Francisco Varela, living organisms are characterized by autopoiesis, which enables their continued existence.

Events to which the self-organizing capacities of organisms, species or other complex systems can adapt, like minor injuries or changes in the physical environment are reversible.