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# The entropy

## A bit of philosophy

### The living world

Le douanier Rousseau

Life on earth produces well-ordered creatures. That seems to deny the second principle of thermodynamics! However: Living creatures absorb food and produce many small and disordered molecules like $CO_2(g)$,$H_2O(g)$,$O_2(g)$,$CH_4$ ..., so the entropy of the system constituted by themselves and their surroundings increases overall!

### Pollution

Vincent Van Gogh

The second principle of thermodynamics states that all spontaneous activity results in an increase of the total entropy of the universe. It means that if we make somewhere some order, disorder must increase in the surroundings. Pollution is the distribution of undesirable substances in the surroundings and is accompanied by an enormous increase in entropy. That is the result of our efforts aiming at neatness and order. For instance if I take the dust from a carpet, the production of electricity consumed by my vacuum cleaner has liberated toxic gases into the air like $SO_2$. These gases can no more been recovered without spending a considerable amount of energy!

### The end of the world

Vincent Van Gogh

All transformations in our world are spontaneous. The second principle of thermodynamics states that all spontaneous transformations result in an increase of entropy. Is therefore the world doomed to finish in a total disorder? Even elementary particles could no more remain because they are somehow ordered ! Philosophers quarrel about that question! The second principle is valid for an isolated system. How about the universe ? Is it an isolated system ?