Condensed concepts

Pierre-Gilles de Gennes  (1932-2007) was arguably the founder of soft matter as a research field, as recognized by  the Nobel Prize in Physics in 1991.  After this de Gennes gave many lectures in French high schools, which were then published as a book,  Fragile Objects: Soft Matter, Hard Science, and the Thrill of Discovery . Previously, I mentioned the book with regard to whether condensed matter physics is too abstract.  One of many fascinating sections of the book is a chapter entitled, The Imperialism of Mathematics . de Gennes sings the praises of chemistry, and rants about the weaknesses of the French system, laying the blame at the feet of his compatriot  Auguste Comte  (1798-1857). Comte was one of the first philosophers of modern science and a founder of sociology and of positivism. Below I reproduce some of the relevant text. When reading it bear in mind that de Gennes was a theoretical physicist and did work that often involved quite abstract mathematics and concepts.     

An important question about emergent properties is whether they can be explained solely in terms of the properties of the components of the system. Here I explore the question from the point of view of Hempel's covering law of scientific explanation , discussed in my last post. According to Hempel, a scientific explanation E of a specific phenomena P is a logical argument that starts with some premises, at least one of which is a scientific law L, and which logically implies P. I now give a version of this that describes a microscopic scientific explanation of some emergent property. Suppose that a macroscopic system S has property X. S is composed of many interacting microscopic components whose properties, including their interactions, have a finite enumeration x1, x2, x3,...xn. None of these properties is X. Hence, in the sense of novelty, X is an emergent property of S. Let l1, l2, l3,.., lm be a finite number of microscopic laws. Then X has a microscopic scientific explanation

An important issue concerning emergent phenomena is whether part of their definition should be that they "cannot be explained/predicted" solely in terms of the properties of the components of the system.  As I have discussed before , there are several alternatives such as difficult to explain, extremely difficult to explain, impossible to explain, and possible to explain in principle, but not in practice... To further consider this issue, it is helpful to back up and consider the general question, "What is a scientific explanation of a specific natural phenomena?" This has received a lot of attention over the past century from philosophers of science. A nice accessible introduction is found in Philosophy of Science: A Very Short Introduction by Samir Okasha . In chapter 3, he discusses at length the Covering Law model of explanation , developed by Carl Hempel . Here are the basic elements of the model. Hempel observed that "scientific explanations typically ha

 An important challenge required to understand the physical properties of materials that are chemically and structurally complex is to ascertain which microscopic details are important. A related question is at what scale (length, number of atoms, energy) models should be developed. A specific example is understanding the magnetic properties and state transitions of spin-crossover materials. This is difficult for equilibrium properties, let alone for non-equilibrium properties such as Light-Induced Excited Spin-State Trapping (LIESST). At low temperatures irradiation with light can induce a transition from the equilibrium low-spin state to a long-lived high-spin state, which is only an equilibrium state at higher temperatures. (LIESST gets a lot of attention because of the potential to make optical memories for information storage). Some of my UQ colleagues recently published a nice paper that elucidates some of the key physics with the proposal and analysis of a (relatively simple) mo

 In the School of Mathematics and Physics at UQ there is an Early- and Mid-Career Academic group who organise activities to support one another. Today they organised a panel discussion on "Mental Health, Wellness and Resilience". I commend them for their initiative. Before covid, they organised a single forum which I spoke at and thought was particularly good. I am one of the panelists. As someone who has struggled with mental health for four decades now, here are a three of the points I want to make. Practise the basics: eat and drink healthy, sleep, rest, exercise, control screen time, and connect to community. Get professional help, sooner than later. Be open to medication, counselling, and expertise.  Live according to your own personal values, rather than those that your boss or university management may want you to have. One of my fellow panelists, Marissa Edwards , brought to our attention this recent article in The Conversation, Where has the joy of working in Austral