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Second Law of Thermodynamics (view source)
Revision as of 03:01, February 7, 2017
, 03:01, February 7, 2017information
In fact, entropy changes locally all the time, on a vastly larger scale than cards, rooms, apples, people, or fires—higher during the day, lower at night, higher in Summer, lower in Winter. Entropy is constantly being "wasted". Where does the entropy reduction required to offset this come from? The Earth is a giant heat engine, with energy from the Sun falling on the daylight side, and "waste" energy emitted into space from the night side. This sunlight powers virtually everything that happens on Earth.
In fact, entropy changes locally all the time, on a vastly larger scale than cards, rooms, apples, people, or fires—higher during the day, lower at night, higher in Summer, lower in Winter. Entropy is constantly being "wasted". Where does the entropy reduction required to offset this come from? The Earth is a giant heat engine, with energy from the Sun falling on the daylight side, and "waste" energy emitted into space from the night side. This sunlight powers virtually everything that happens on Earth.
==Entropy and information==
Information is in the eye of the beholder. The first ten million digits of pi can be considerd to be a very precise and detailed piece of information, or they can be considered to be ten million digits of random garbage.<ref>The digits of pi are believed to be truly random. They have passed every statistical test for randomness. No patterns are known.</ref> In the former case, the digits have an entropy of zero; in the latter case the entropy is 3.2 x 10<sup>-21</sup> Joules per Kelvin.
The entropy of the human genome, in each cell, is 6 x 10<sup>-14</sup> Joules per Kelvin when the base pairs are considered to be random, and zero when the base pairs are in a given human's specific genetic configuration. The metabolism of 2.5 x 10<sup>-22</sup> grams of sugar can provide the "entropy budget" to copy a cell's genome. That is, to turn the random base pairs floating in the intracellular fluid into a copy of an existing set of chromosomes. This is done every time a cell divides. Of course the process is far from 100% efficient. 10<sup>-8</sup> grams of sugar are sufficient, under 100% thermodynamic efficiency, to copy the DNA of all the cells in one's body. Avogadro's number really is very large.
==Reversibility and irreversibility==
==Reversibility and irreversibility==