Tag Archives: Thermodynamics

Fridges slow down time

Photograph of the interior of a large domestic fridgeWe sense the passage of time by the changes that occur around us (see ‘We inhabit time as fish live in water‘ on July 24th, 2019) and these changes are brought about by processes that generate entropy.   Entropy is often referred to as the arrow of time because forwards in time is always the direction in which the entropy of the universe increases, as demanded by the second law of thermodynamics (see for example ‘Subtle balance of sustainable orderliness‘ on June 22nd, 2016).  The temperature in a refrigerator is sufficiently low that it slows down the processes of decay in the food stored in it (see’ Life-time battle‘ on January 30th, 2013) which effectively slows down time locally in the fridge.  However, there is a price to pay because the process of creating of the cold zone in the fridge increases the entropy in the universe and moves the universe infinitesimally closer to cosmic heat death (see ‘Will it all be over soon?‘ on November 2nd, 2016).  So, cooling the food in your fridge slows down time locally but brings the end of the universe a tiny bit closer.  Perhaps that’s not worth worrying about until you start thinking about how many fridges there are in the world (about half a billion are sold every year) and how many other devices are generating entropy.  The end of the universe might still be billions of years away but all that anthropogenic entropy is contributing to the increase in the temperature of the Earth’s ecosystem.

Are these the laws of engineering?

While shopping on-line for books during a pandemic lockdown allows you to buy new books, I found it difficult browse online and find new authors. Perhaps because the algorithms employed by the booksellers are too busy guessing my interests or promoting the latest book that they want me to buy. So it was a pleasure to be able to walk into a bookshop again in a couple of months ago. One of the new authors that I discovered was Niall Williams. I have just finished reading his 2019 novel ‘This is happiness‘ which weaves together the life of an Irish village in which nothing ever changes until the coming of electricity, a tale of coming of age and another of burying the past. In the middle of this beautifully-told story, a salesman is extolling the virtues of the electrical gadgets that they can install in their new electrified homes and says that ‘the first law of engineering was to make the world a better place’. The narrator quietly tells us the second law, which the salesman doesn’t state, ‘that without exception everything that was engineered would one day break down … usually one day after each machine had become indispensable to living’. This is a consequence of the second law of thermodynamics, which is that entropy, or disorder, increases in all real processes. Hence, the localised order, which we create when something is engineered, is constantly being eroded until eventually the disorder leads to a break down. Or, as Murphy’s law states ‘Anything that can go wrong will go wrong’. However, the definition of the first law of engineering was the one that caught my eye and resonated with a corny introduction that I used in a talk on why we need to change the way we teach engineering. I played a recording of Louis Armstrong singing ‘What a wonderful world‘ and then talked about the wonderful world that engineers have created before highlighting the unsustainable environmental costs of our ‘wonderful’ engineered world and that it is inaccessible to a large portion of the world’s population. I gave that talk many times to groups of engineering professors in the USA between about 2006 and 2012; maybe I had some impact but there is still a lot of changes needed to achieve a sustainable society. So, the first law of engineering should be to make the world a better place for everyone.


Niall Williams, This is happiness, London: Bloomsbury Publishing, 2019

Limited bandwidth

Photograph of hills with walking boots in foregroundMany people take a week’s holiday at this time in the UK because Monday was the Spring Bank Holiday. We went walking in the Clwydian hills which we can see from our house to the south-west across the rivers Mersey and Dee. However, despite the walking on the wild side [see ‘Take a walk on the wild side‘ on August 26th, 2015], I did not feel particularly creative when I sat down to write this week’s blog post. Together with most of my academic colleagues, I am in the midst of reviewing student dissertations and marking end of year assessments. I have written in the past about the process of marking examinations and the tens of thousands of decisions involved in marking a large pile of scripts [see ‘Depressed by exams‘ on January 31st, 2018]. However, the constraints imposed by the pandemic have changed this process for students and examiners because the whole exercise is conducted on-line. I have set an open-book examination in thermodynamics which the students completed online in a specified time period and submitted electronically. Their scripts were checked automatically for plagiarism during the submission process and now I have to mark about 250 scripts online. At the moment, marking online is a slower process than for hardcopy scripts but perhaps that’s a lack of skill and experience on my part. However, it seems to have same impact on my creativity by using up my mental bandwidth and impeding my ability to write an interesting blog post [see ‘Depressed by exams‘ on January 31st, 2018]!

Everything is flux but it’s not always been recognised

Decorative photograph or ruins of Fountains Abbey next to River SkellI am teaching thermodynamics to first year undergraduate students at the moment and in most previous years this experience has stimulated me to blog about thermodynamics [for example: ‘Isolated systems in nature?’ on February 12th, 2020].  However, this year I am more than half-way through the module and this is the first post on the topic.  Perhaps that is an impact of teaching on-line via live broadcasts rather than the performance involved in lecturing to hundreds of students in a lecture theatre.  Last week I introduced the second law of thermodynamics and explained its origins in efforts to improve the efficiency of steam engines by 19th century engineers and physicists, including Rudolf Clausius (1822 – 1888), William Thomson (1827 – 1907) and Ludwig Boltzmann (1844 – 1906).  The second law of thermodynamics states that the entropy of the universe increases during all real processes, where entropy can be described as the degree of disorder. The traditional narrative is that thermodynamics was developed by the Victorians; however, I think that the ancient Greeks had a pretty good understanding of it without calling it thermodynamics.  Heraclitus (c. 535 BCE – c. 475 BCE) understood that everything is in flux and nothing is at rest so that the world is one colossal process.  This concept comes close to the modern interpretation of the second of law of thermodynamics in which the entropy in the universe is constantly increasing leading to continuous change.  Heraclitus just did not state the direction of flux.  Unfortunately, Plato (c. 429 BCE – c. 347 BCE) did not agree with Heraclitus, but thought that some divine intervention had imposed order on pre-existing chaos to create an ordered universe, which precludes a constant flux and probably set back Western thought for a couple of millennia.  However, it seems likely that in the 17th century, Newton (1643 – 1727) and Leibniz (1646 – 1716), when they independently invented calculus, had more than an inkling about everything being in flux.  In the 18th century, the pioneering geologist James Hutton (1726 – 1797), while examining the tilted layers of the cliff at Siccar Point in Berwickshire, realised that the Earth was not simply created but instead is in a state of constant flux.  His ideas were spurned at the time and he was accused of atheism.  Boltzmann also had to vigorously defend his ideas to such an extent that his mental health deteriorated and he committed suicide while on vacation with his wife and daughter.  Today, it is widely accepted that the second law of thermodynamics governs all natural and synthetic processes, and many people have heard of entropy [see ‘Entropy on the brain’ on November 29th, 2017] but far fewer understand it [see ‘Two cultures’ on March 5th, 2013].  It is perhaps still controversial to talk about the theoretical long-term consequence of the second law, which is cosmic heat death corresponding to an equilibrium state of maximum entropy and uniform temperature across the universe such that nothing happens and life cannot exist [see ‘Will it all be over soon?’ on November 2nd, 2016].  This concept caused problems to 19th century thinkers, particular James Clerk Maxwell (1831 – 1979), and even perhaps to Plato who theorised two worlds in his theory of forms, one unchanging and the other in constant change, maybe in an effort to dodge the potential implications of degeneration of the universe into chaos.

Image: decaying ruins of Fountains Abbey beside the River Skell.  Heraclitus is reported to have said ‘no man ever steps twice into the same river; for it’s not the same river and he’s not the same man’.