Category Archives: Learning & Teaching

Storm in a computer

Decorative painting of a stormy seascapeAs part of my undergraduate course on thermodynamics [see ‘Change in focus’ on October 5th, 2022) and in my MOOC on Thermodynamics in Everyday Life [See ‘Engaging learners on-line‘ on May 25th, 2016], I used to ask students to read Chapter 1 ‘The Storm in the Computer’ from Philosophy and Simulation: The Emergence of Synthetic Reason by Manuel Delanda.  It is a mind-stretching read and I recommended that students read it at least twice in order to appreciate its messages.  To support their learning, I provided them with a précis of the chapter that is reproduced below in a slightly modified form.

At the start of the chapter, the simplest emergent properties, such as the temperature and pressure of a body of water in a container, are discussed [see ‘Emergent properties’ on September 16th, 2015].  These properties are described as emergent because they are not the property of a single component of the system, that is individual water molecules but are features of the system as a whole.  They arise from an objective averaging process for the billions of molecules of water in the container.  The discussion is extended to two bodies of water, one hot and one cold brought into contact within one another.  An average temperature will emerge with a redistribution of molecules to create a less ordered state.  The spontaneous flow of energy, as temperature differences cancel themselves, is identified as an important driver or capability, especially when the hot body is continually refreshed by a fire, for instance.  Engineers harness energy gradients or differences and the resultant energy flow to do useful work, for instance in turbines.

However, Delanda does not deviate to discuss how engineers exploit energy gradients.  Instead he identifies the spontaneous flow of molecules, as they self-organise across an energy gradient, as the driver of circulatory flows in the oceans and atmosphere, known as convection cells.  Five to eight convections cells can merge in the atmosphere to form a thunderstorm.  In thunderstorms, when the rising water vapour becomes rain, the phase transition from vapour to liquid releases latent heat or energy that helps sustain the storm system.  At the same time, gradients in electrical charge between the upper and lower sections of the storm generate lightening.

Delanda highlights that emergent properties can be established by elucidating the mechanisms that produce them at one scale and these emergent properties can become the components of a phenomenon at a much larger scale.  This allows scientists and engineers to construct models that take for granted the existence of emergent properties at one scale to explain behaviour at another, which is called ‘mechanism-independence’.  For example, it is unnecessary to model molecular movement to predict heat transfer.  These ideas allow simulations to replicate behaviour at the system level without the need for high-fidelity representations at all scales.  The art of modelling is the ability to decide what changes do, and what changes do not, make a difference, i.e., what to include and exclude.


Manuel Delanda Philosophy and Simulation: The Emergence of Synthetic Reason, Continuum, London, 2011.

Image: Painting by Sarah Evans owned by the author.

Celebrating engineering success

Today is National Engineering Day [see ‘My Engineering Day’ on November 4th, 2021] whose purpose is to highlight to society how engineers improve lives.  I would like to celebrate the success of two engineers who are amongst the seventy-two engineers elected to the fellowship of the Royal Academy of Engineering this year.  Chris Waldon is leading the design and delivery of a prototype fusion energy plant, targeting 2040, and a path to the commercial viability of fusion.  This is a hugely ambitious undertaking that has the potential to transform our energy supply.  He is the first chief engineer to move the delivery date to within twenty years rather than pushing it further into the future.  My other featured engineer is Elena Rodriguez-Falcon, a leading advocate of innovations in engineering education that focus on encouraging enterprising and socially-conscious approaches to designing and delivering engineering solutions.  These are important developments because we urgently need a more holistic, sustainable and liberal engineering education that produces engineers equipped to tackle the complex challenges facing society.  Of course I am biased having worked and published with both of them.  However, I am not alone in my regard for them and will be joining other Fellows of the Royal Academy of Engineering at a dinner in London next week to celebrate their achievements.

A sign of normality returning

I am in the midst of marking examination scripts.  I have about two weeks to award a maximum of about 26,000 marks which is a huge number of decisions to make in a relatively short time [see ‘Depressed by exams‘ on January 31st 2018].  Although the pile of examination scripts is tall and the task can feel overwhelming, it represents a return to normality following the pandemic when we conducted on-line, open-book examinations [see ‘Limited bandwidth’ on June 2nd, 2021].  We have been teaching 100% on-campus for the whole semester and all of our examinations have returned to their pre-pandemic format, i.e., the majority have been in-person, closed-book and invigilated.  I have enjoyed teaching thermodynamics in a huge lecture-theatre filled with students and it is relief that I do not have to set examination questions whose answers cannot be found using a search engine or solved using a programme.  Anyway I need to pick up my red pen and return to my marking so only a brief post this week.

From nozzles and diffusers to stars and stripes

Schematic diagram of explanation in textAt the end of a lecture on energy flows in my first year undergraduate course on thermodynamics, I talk about nozzles and diffusers as examples of practical applications of the rest of the material in the lecture.  It is hazardous to sit in the front row of the lecture theatre because I take in a water bottle with a trigger spray to demonstrate how the nozzle increases the velocity of the fluid at the expense of pressure while gently sprinkling water on the front row.  I am always intrigued by the symmetry of nozzles and diffusers.  Diffusers increase pressure of a fluid at the expense of its velocity, i.e., a mirror image of the action of a nozzle.  The cross-sections are also mirror images because a nozzle has a cross-section that decreases in the flow direction while a diffuser has a cross-section that increases in the flow direction.  At least for sub-sonic flows, because the shapes are reversed for super-sonic flow; so a sub-sonic nozzle looks like a super-sonic diffuser and a sub-sonic diffuser looks like a super-sonic nozzle.  If that all sounds like fluid mechanics then the thermodynamic message is that, in nozzles and diffusers, the rates of heat and work transfer are approximately zero while the change in the kinetic energy of the fluid is very large.  I finish the lecture with a video clip of a school quartet of trombones playing ‘Stars and Stripes Forever’ which wakes up the students who have slept through the lecture and allows me to point out the diffusers (bell of the trombone) transmitting acoustic pressure.

You can watch the video clip on YouTube at