First posted 19 December 2011
Absolute zero is the temperature at which all thermal energy is removed from a molecule. Absolute zero really is very chilly! Actually it’s −273.15 °C.
But how did the study of temperature, heat and the field of thermodynamics begin? How did we get to the point where we know that at roughly minus 273.15 ° Celsius all the thermal energy is removed from a molecule? Actually, why is it even the Celsius scale? What started it all?
It was with the invention of a thermometer.
The story of the thermometer includes a number of science heroes, and this is a brief introduction to the story. It doesn’t cover everything, how could it, in one thousand words. But it is an interesting story, one which deserves some attention.
The story begins in about 1592, when Galileo (our first science star), is said to have invented the first thermoscope – or air thermometer. Many developments, by a number of people later, in 1641, the grand duke of Tuscany, Ferdinand II included a sealed alcohol indicator on his thermoscope. This development allowed temperature to be measured independently to air pressure.
Importantly, both Galileo’s and Ferdinand II’s themoscopes only included an arbitrary scale. Making them both interesting curiosities rather than scientific instruments. From these theromoscopes you could have an idea about how temperature changes over short periods of time in one location, but there was no way of relating the readings to each other over longer time scales or the differences between two thermoscopes in different locations. Not actually very useful.
Many experimented with the design of the thermometer. Meet Sir Isaac Newton, he’s quite well known. Perhaps most popular for the falling apple/gravity escapade. But also for many laws on relativity and motion. Less well known is Newtons Law of Cooling and his foray into Thermodynamics (the study of temperature and heat).
At the beginning of the 18th Century (1701 to be precise) Newton suggested an oil thermometer with a ‘rational thermometric scale’. On his scale, the temperature of freezing water was 0° and the temperature of ‘the healthy human body’, 12°. This really was an interesting development, if a standard scale could be agreed on and used by the world then science could really begin to experiment with heat and temperature
As a result of this idea and the subsequent experimentation with thermometers, Newton developed his ‘Law of Cooling’. This law states, ‘The cooling of a hot body is proportional to the difference in temperature between that body and the medium by which it is surrounded’.
It does sound a bit complicated when written in the formal and antiquated style of 18th Century science. What is really means is: A thing (body) will cool at a given rate. The rate is dependant on the difference in the temperature of the body and it’s surroundings.
The surroundings could be anything, a liquid say water, a gas perhaps air, or a solid for instance rock. Newtons Law of Cooling, as it is now known, combined with the development an accurate thermometer and the idea of thermometric scale, made huge leaps possible in the emerging field of thermodynamics.
Others also proposed standard scales before Newton’s 12 degree scale, Christiaan Huygens suggested using the melting and boiling points of water as standards, and in 1694 Carlo Renaldini proposed using these points on a universal scale. The development of the thermometer, as with most scientific endeavours, really was a group effort.
The next important development for the thermometer was made by another name that might be familiar. D. G. Fahrenheit invented and manufactured the mercury thermometer from around 1715. He had an advantage over the others. Because he manufactured the thermometers in bulk, his standard scale caught on more widely.
Fahrenheit’s mercury thermometer allowed the accurate measurement of temperatures in a scale that was accurate and that could be repeated in different locations. This breakthrough allowed the quantitative science of heat to begin. This new science was pioneered by Joseph Black (1728 – 1799). In around 1760 Black introduced measuring quantities of head by degrees.
The modern Farenheit scale is said to be based upon the temperature range that humans regularly experience on earth (in the 18th Century). This means that 100°F is the temperature of a human body in health (thanks Newton), and 0°F is something like the coldest temperature that a human might experience.
Anders Celsius came up with the 100 point scale in 1742 – with 100 being the temperature of freezing water and 0 the boiling point of water. The scale we know as the Celcius scale of course has these the other way around.
Before Joseph Black and the study of thermodynamics, the belief was that the quantity of a substance determined the temperature. Black realised and proved that each and every substance had a characteristic ‘capacity for heat’, what scientists now call ‘Specific Heat’.
Not content with ‘Specific Heat’, Black also “discovered” latent heat. Something that could take up a whole article here, or in fact a whole book. In brief, Black showed that as a substance changes it’s physical state (e.g. from a liquid to a solid), energy disappears or appears. During melting (solid to liquid) and evaporation (liquid to gas) energy is lost from the substance. It ‘dissapears’ or more accurately, it is lost to the system (whatever surrounds the substance).
The reverse is also true, when a substance freezes (liquid to solid) or condenses (liquid to las) energy reappears within the substance. Uncanny!
The reason we can measure just how chilly anything actually is, is thanks to the cast of our story here, and needless to say countless other people who have been forgotten by time, and probably quite a number forgotten or not included here.
One person who is central to the absolute zero story is Lord Kelvin. He has his own temperature scale, and is a big player in the world of thermodynamics. But I have run out of words, perhaps in another article, on another day Kelvin will have his story told in my haphazard way.
987 words
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