Is a coconut an isolated thermodynamic system? This is a question that I have been thinking about this week. A coconut appears to be impermeable to matter since its milk does not leak out and it might be insulated against heat transfer because its husk is used for insulation in some building products. If you are wondering why I am pondering such matters, then it is because, once again, I am teaching thermodynamics to our first year students (see ‘Pluralistic Ignorance‘ on May 1st, 2019). It is a class of more than 200 students and I am using a blended learning environment (post on 14th November 2018) that combines lectures with the units of the massive open online course (MOOC) that I developed some years ago (see ‘Engaging learners on-line‘ on May 25th, 2016). However, before devotees of MOOCs get excited, I should add that the online course is neither massive nor open because we have restricted it to our university students. In my first lecture, I talked about the concept of defining the system of interest for thermodynamic analysis by drawing boundaries (see ‘Drawing boundaries‘ on December 19th, 2012). The choice of the system boundary has a strong influence on the answers we will obtain and the simplicity of the analysis we will need to perform. For instance, drawing the system boundary around an electric car makes it appear carbon neutral and very efficient but including the fossil fuel power station that provides the electricity reveals substantial carbon emissions and significant reductions in efficiency. I also talked about different types of system, for example: open systems across whose boundaries both matter and energy can move; closed systems that do not allow matter to flow across their boundaries but allow energy transfers; and, isolated systems that do not permit energy or matter to transfer across their boundaries. It is difficult to identify closed systems in nature (see ‘Revisiting closed systems in nature‘ on October 5th, 2016); and so, once again I asked the students to suggest candidates but then I started to think about examples of isolated systems. I suspect that completely isolated systems do not exist; however, some systems can be approximated to the concept and considering them to be so, simplifies their analysis. However, I am happy to be corrected if anyone can think of one!
It is the beginning of the academic year and once again I am teaching introductory thermodynamics to engineering undergraduate students and my MOOC entitled ‘Energy: Thermodynamics in Everyday Life‘ is running in parallel. Last week after my lecture on thermodynamic systems, a student approached me to ask whether the universe is a closed and isolated system. It’s an interesting question and the answer is depends on the definition of universe. In thermodynamics, we usually define a boundary to delineate the system of interest as everything inside the boundary and everything else are the surroundings. The system and surroundings taken together are the universe (see my post ‘No beginning or end‘ on February 24th, 2016). If the universe is defined as the system then there are no surroundings; hence the system cannot exchange energy or matter with anything which is the definition of a closed and isolated system.
Physicists often refer to the observable universe, or define the universe as everything we can observe. We are aware that we cannot observe everything. Hence, it is reasonable to suppose that the observable universe exchanges energy and matter with the unobservable space beyond it, in which case the observable universe is an open system. We could also consider the concept that we are part of multiverse and our universe is only one of many, in which case it seems likely that is not isolated, i.e. it can exchange energy, and perhaps it is open, i.e. it can exchange both energy and matter with other parts of the multiverse.