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i40

Entropy

System and system boundaries

In thermodynamics a system is defined as the quantity of matter and space which is observed in the context of a given scientific study. The remainder of the world is called the surroundings of the system. To avoid ambiguities the boundaries of a given system should be accurately defined.

All human activities occur within the biosphere, a thin layer around the Earth in which life has developed and can exist. The biosphere is the only place where human life is possible. From a thermodynamic point of view it may be obvious to consider the biosphere as the surroundings of all human systems and activities. The biosphere in itself is a finite system, an observation with far-reaching consequences.

If we want, for example, to analyse the impact of nuclear power on the human environment, the complete nuclear process chain should be the observed system and the biosphere its surroundings.

Definition of entropy

Entropy is the key notion in understanding the Second Law and with this law of many basal phenomena of nature. The definition of entropy can be formulated in various ways, here we use the description:

Entropy is a measure of dispersal and randomness of matter, of energy and of oriented movement. A more random distribution of matter and energy in a system means a higher entropy of the system.

This probabilistic approach of the notion entropy is based on the quantization of matter and energy. Matter consists of elementary particles, atoms and molecules, and energy transfer occurs in small discrete steps, called energy quanta. An example of energy quanta are photons: a photon is the smallest quantity of light.

Entropy changes

In practice we only observe entropy changes of a system. For understanding some basics of nuclear power and sustainable energy a semiquantitative approach of entropy changes satisfies: we only need to know if the entropy of a system increases or decreases by a given action or phenomenon.

A rise of the entropy of a system means more randomness: more dispersion of matter, energy and directional movement, or in other words: a loss of quality and usefulness of the observed system. For that reason entropy may be described in non-physical terms as a measure of 'mess and uselessness'.

An entropy reduction of a system means less randomness and a gain of quality and usefulness of the system.

When a steel tube rusts and decays into a pile of brown grains, the mess and uselessness of the original amount of steel have increased, or in thermodynamic terms: the entropy of the system has increased. The amount of iron in the observed system has not changed: the iron atoms of the original tube are still present in the pile of rust grains.

The following phrase is a metaphor of an entropy increase, as result of a spontaneous process: Any fool can pour a cup of tea into the ocean, but a thousand wise men cannot pull it out again.

Observable anthropogenic entropy effects in the biosphere

All human activities are occurring within the biosphere, so all entropy effects of the human activities remain within the biosphere. The biosphere is the only system in which human life is possible.

A rise of the entropy of the biosphere caused by human activities manifests itself as deterioration of the environment and loss of quality of ecosystem services. In fact, all anthropogenic environmental problems are entropy effects. This is not difficult to recognize, for these are caused by dispersion of matter and energy and by degradation of the usefullness of ecosystem services. At the present conditions the netresult of the human activities is degradation of the quality of ecosystems, causing loss of functionality and loss of usefullness to humankind. Examples of anthropogenic entropy effects are:

• dispersion of CO2 and other human-made greenhouse gases throughout the atmosphere

• pollution of air by dust, soot, acidifying and radioactive gases

• pollution of ground water, rivers, lakes, sea, air and soil by anthropogenic chemicals

• oil spills

• destruction of ecosystems by mining

• dispersion af radioactive materials into the air, water and soil

• erosion of arable land, loss of topsoil, degradation and decline in soil fertility

• washout of phosphate fertilizers into rivers and sea

• desert forming by overgrazing of grasslands

• decline of biodiversity decline of fish populations in the sea

• deforestation

• loss of irreplaceable materials,such as platinum and phosphates

• rising global temperatures by greenhouse gas emissions.

Most of these entropy effects are irreversible on human timescales.

Ordered materials, functionality and entropy

Materials in the context of economy and society generally are processed materials, for example metals, medicines and plastics. These ordered materials have desired and predictable properties and a high usefullness for specific purposes.

How well is a given material or piece of equipment suited to perform a given task, and what is the mean time between failures? These questions refer to the functionality and reliability of materials and constructions. Functionality has to do with the specific properties of a piece of equipment and the materials it is made from. Reliability has to do with the predictability of the behaviour of the equipment and materials under operational conditions of wear, stress and corrosion.

Increasing the functionality and reliability of materials and machines is the opposite of a spontaneous process and is only possible by means of dedicated effort and investment of useful energy. Degradation of functionality and reliability, that means increase of the entropy of the system, is a spontaneous process.

The more specialistic the task, the higher the required quality standards of materials, design and craftsmanship for production of the material and/or object, and consequently the higher energy input. A higher functionality, or quality, requires a higher investment of useful energy and human skill. This observation follows directly from the Second Law.

Even the most reliable components will ultimately fail as a result of spontaneous processes. Lowering the chance of failure, requires higher quality standards of materials and dimensioning of each component. The chance of a failure can be reduced by maintenance and investment of useful energy, but cannot be eliminated. For that reason an inherent safe nuclear reactor is inherently impossible [more i15].

Fallacy of economic growth

The following view is a widespread fallacy:

"The economy has to grow to generate the economic means necessary to compensate for the environmental problems."

Environmental problems are observable consequences of anthropogenic entropy generation. History shows that economic growth invariably implies a growth of the consumption of energy and raw materials and consequently an ever increasing environmental deterioration.

From the Second Law follows [more i41] that the generation of useful energy from mineral energy sources generates more entropy than can be compensated for by the corresponding amount of useful energy. Compensation of one unit entropy (environmental mess) generated in the past, a multiple of units of entropy would be generated today, irrevocably coupled to the generation of the required amount of useful energy. Besides, most anthropogenic entropy effects are irreversible as noted above.

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