Tag Archives: entropy

Arbitrary zero

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thermometerAs mentioned in my previous post (Lincoln On Equality, 6th February, 2013), the Zeroth Law of Thermodynamics enables the concept of temperature and temperature scales to be established.  The Swedish astronomer, Anders Celsius (1701-44) devised a temperature scale on which water froze at 100 degrees and boiled at zero, i.e. the opposite way around to the scale that bears his name today.  Daniel Fahrenheit (1686-1736), a German instrument maker, was probably the first to use a mercury thermometer and he assigned zero to the lowest temperature he could achieve, which was for a mixture of salt and water.  He chose his body temperature as 100 degrees because it was an easily portable standard, but not ideal because it is not totally reproducible.  Fahrenheit’s scale had a temporary advantage because negative numbers were rarely needed given the technology of the day and that water freezes at 32 degrees Fahrenheit.

Somewhat later it was decided that it might be more appropriate to set zero as the lowest attainable temperature, known as absolute zero, which is defined by the Third Law of Thermodynamics as the temperature at which the entropy of all perfectly crystalline pure substances is zero.  This lead to definition of two temperature scales: the Kelvin scale with degrees the same size as on the Celsius scale so that water freezes and boils at 273K and 373K respectively; and the Rankine scale with degrees the same size as the Fahrenheit scale.

Actually, absolute zero is not attainable.  The world record stands at 810 trillionths of a degree Rankine (see http://www.smithsonianmag.com/science-nature/phenom-200801.html).

Image credit: arztsamui / FreeDigitalPhotos.net

Life-time battle

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163-6306_IMGLife is a constant battle against entropy.  All living things are well-ordered structures with low entropy (degree of disorder) and the second law of thermodynamics demands that entropy levels are always trying to increase.  Animals fight this tendency by eating low entropy plants (or other animals), breaking them down to release entropy, thus satisfying the second law, and retaining low entropy components, i.e. highly-ordered and high energy molecules such as glucose.  If we stop eating, our bodies start to disintegrate and we die – entropy wins as the molecules of bodies are dispersed.

Plants use sunlight to fight the entropic battle.  In photosynthesis, low entropy solar energy converts carbon dioxide and water  to oxygen and glucose with the creation of entropy in the form of dispersed heat.

Food waste

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korea cafeteriaIt has been reported recently that there are more people suffering from obesity in the world than from malnutrition (http://www.ifrc.org/en/publications-and-reports/world-disasters-report/wdr2011/).  This might suggest that global society has a major distribution problem to solve and that current approaches are failing.  This is a tentative conclusion supported by another recent report which estimates that half of global food production is wasted (http://www.imeche.org/knowledge/themes/environment/global-food).  Some agricultural production never reaches the distribution system and rots in the fields, while some is disposed of untouched by end-purchasers.  Presumably end-purchasers throwing away uneaten food are not starving and probably a high proportion of them are obese.

The second law of thermodynamics demands that there must be waste in all processes, so we can never reduce the wasted food production to zero but 50% wastage seems high and perhaps implies we some way to go before population growth is limited by food production (see post on ‘Two Earths’ in August 13th, 2012 or ‘Population crunch’ on September 15th, 2012).  Of course, if the majority of current food production is unsustainable then we are in trouble already.

Unavoidable junk

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167-6734_IMGThe laws of thermodynamics are physical laws whose relevance extend beyond the study of engines and heat plants.  We can restate the first law of thermodynamics (conservation of energy) as ‘the quantity of matter is constant and finite’.  Matter changes both in nature and as it moves through the economic system; and as it does so, its intrinsic properties change rendering it less useful and usable, thus requiring more and more resources to make it useful again.  This last sentence is a form of the second law of thermodynamics.  Very useful (low entropy) goods, such as iron ore and fossil fuels, eventually produce less useful (high entropy) matter, such as piles of junk cars in scrap-metal yards and greenhouse gases, as they move through the economic system.  In our current western life-style, we are all contributing to the generation of vast piles of junk; we are hooked on it; we are all ‘junkies’.

In the paragraph above, I have plagiarised the 2009 report entitled ‘The New Sustainable Frontier’ mentioned in the previous posting on this blog [http://www.gsa.gov/graphics/ogp/2009_New_Sustainable_Frontier_Complete_Guide.pdf ].  However, similar ideas were expressed by Handscombe and Patterson in their 2004 book entitled the ‘Entropy Vector’ [http://www.worldscientific.com/worldscibooks/10.1142/5365 ].  They paraphrased the first and second laws of thermodynamics as ‘you can’t have something nothing’ and ‘you can’t have it just anyway you like it’.