Tag Archives: science

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

Lincoln on equality

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I watched Steven Spielberg’s movie ‘Lincoln’ recently.  Lincoln is portrayed as quoting Euclid on equality: ‘Things that are equal to the same things are equal to each other’.  This is from Euclid’s book ‘Elements’ which was in common use until modern times as a mathematics textbook and is believed to have sold more copies than any other book besides the Bible.  In the movie Lincoln extends the meaning of this first of Euclid’s ten axioms from mathematics to embrace the equality of men.  Since I am teaching thermodynamics at the moment, I was struck by its similarity to the zeroth law of thermodynamics, which states that ‘two systems in thermal equilibrium with a third system  are also in thermal equilibrium with each other’.  The concept of the zeroth law is sometimes accredited to Rankine who lived in the middle of the 19th century, or more than two thousand years after Euclid (380BC – 260BC).  It is reputed to be called the zeroth law because it was only recognised as being of fundamental importance to thermodynamics after the first and second laws were well-established and to rename them would have caused confusion.  The zeroth law allows temperature and temperature scales to be defined.  It seems to me to be a special case of Euclid’s first axiom ‘Things that are equal to the same things are equal to each other’, and that it is remarkable that it took the fathers of thermodynamics so long to recognise it, especially when they were probably brought up on Euclid’s ‘Elements’ as their mathematics textbook at school.

Impact vs. breakthrough

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Last week I was at a meeting to recommend the award of research grants to scientists and engineers at universities.  Weighing the relative merits of research proposals from physical scientists and from engineers is a little like trying to compare chalk and cheese.  The scientists at such meetings tend to argue that none of the engineering research proposals will lead to scientific breakthroughs, which is one criterion for the awarding of grants; while engineers might suggest that the societal impact of scientific research proposals are intangible and remote.  There is an element of truth in both perspectives since broadly speaking engineering is about the application of science for the benefit of society.  Scientists need to make breakthroughs so that there are new ideas for engineers to apply; however often it is not clear how to apply the breakthrough beneficially, reliably, safely and cheaply, thus engineers also to perform research to establish the best route to the application of existing breakthroughs.

Or to quote Einstein: ‘scientists investigate that which already is; engineers create that which has never been’.