Condensed concepts

What are the most amazing things that we know about the physics of the universe? If you were to pick ten what would they be? I recently read Fundamentals: Ten Keys to Reality (2021) a popular science book by Frank Wilczek. My interest in the book was piqued just to see what Wilczek's choices for his "ten" were. I got a copy from the public library and became entranced because I discovered what a gifted writer and expositor Wilczek is. I found I was learning some physics I did not know; or at least getting a deeper understanding of what I should know. I then bought my own copy so I could annotate it. I have previously enjoyed the insights in many of Wilczeks' Physics Today columns. The book gives a popular presentation of some physics "basics" such as celestial mechanics, the Standard Model of elementary particles (which he renames the Core), and Big Bang cosmology.  I found it full of insights. I also appreciated that Wilczek does not have the hard reductio

How should we live? What really exists? And how do we know for sure?  These three questions are at the heart of philosophy as an academic discipline.  This raises the question as to what the "philosophy of physics" is and what it should be? Philosophy of Physics: A Very Short Introduction by David Wallace explores this. He begins by stating that "Daniel Dennett defines philosophy as what we do when we don't know what questions to ask." I found that somewhat unsatisfying and went to The Oxford Companion to Philosophy.  Most definitions of philosophy are fairly controversial, particularly if they aim to be at all interesting or profound. That is partly because what has been called philosophy has changed radically in scope in the course of history, with many inquiries that were originally part of it having detached themselves from it. The shortest definition, and it is quite a good one, is that philosophy is thinking about thinking. That brings out the generally s

 Members of my family have been reading  Phosphorescence: On awe, wonder, and things that sustain you when the world goes dark , a personal memoir by  Julia Baird . This reminded me of how amazing and fascinating bioluminescence is, stimulating me to read more on the science side. One of the first things is to distinguish between bioluminescence, fluorescence, and phosphorescence. Bioluminescence is chemical luminescence whereby a biomolecule emits a photon through the radiative decay of a singlet excited state that is produced by a chemical reaction.  In contrast, fluorescence occurs when the singlet excited state is produced by the molecule absorbing a photon. Phosphorescence occurs when a molecule emits a photon through the radiative decay of an excited triplet state, that was produced by the absorption of a photon. Bioluminescence can occur in the dark. Fluorescence cannot as there are no photons to absorb. Phosphorescence is sometimes seen in the dark but this is because the molec

The physics department at the University of Queensland has just advertised for a junior faculty position in condensed matter. Only applications from women will be considered. The advertisement is here and the closing date is January 19. The photo is of the beach at Bribie Island, my favourite holiday location, about one hours drive away. Aside: it was gratifying that the last faculty hired in condensed matter at UQ, Peter Jacobson, first heard about the position on this blog.

 Is real scientific progress slowing? Are funders of research, whether governments, corporations, or philanthropies, getting a good return on their investment? Along with many others (based largely on intuition and anecdote) I believe that the system is broken, and at many different levels. What are possible ways forward? How might current systems of funding be reformed? The Economist recently published a fascinating column (in the Finance and Economics section!), How to escape scientific stagnation . It reviews a number of recent papers by economists that wrestle with questions such as those above. Philanthropists... funding of basic research has nearly doubled in the past decade. All these efforts aim to help science get back its risk-loving mojo. In a working paper published last year, Chiara Franzoni and Paula Stephan look at a number of measures of risk, based on analyses of text and the variability of citations. These suggest science’s reward structure discourages academics fro

Go to the ant, you sluggard;      consider its ways and be wise! It has no commander,      no overseer or ruler, yet it stores its provisions in summer and gathers its food at harvest.      Proverbs 6:6-8 Ant colonies are amazing. It is incredible what they can achieve. I love the video below. It highlights how complex structures and functions emerge in an ant colony even though there is no individual directing the whole operation. Ant colonies are often cited as an example of emergence, including how complexity can emerge from simple rules. Ant colonies  feature in  Godel, Escher, Bach by Douglas Hofstadter, Emergence: from chaos to order  by John Holland , and Emergence: The Connected Lives of Ants, Brains, Cities, and Software by Steven Johnson. Important steps towards describing and understanding a system with emergent properties include identifying how to break down the system into single components and determining how those components interact with one another. A

Equitable access to good education is a desirable goal. Yet it rarely happens and debate about how to achieve it can be diluted by focusing on access to elite institutions and on "culture war" rhetoric. This week The Economist had a leader (editorial) about admission policies for universities in the USA. Below I reproduce some of the leader, highlighting some points I found poignant. A diversity of backgrounds in elite institutions is a desirable goal. In pursuing it, though, how much violence should be done to other liberal principles—fairness, meritocracy, the treatment of people as individuals and not avatars for their group identities? At present, the size of racial preferences is large and hard to defend. The child of two college-educated Nigerian immigrants probably has more advantages in life than the child of an Asian taxi driver or a white child born into Appalachian poverty. Such backgrounds all add to diversity. But, under the current regime, the first is heavil

 Exactly seventy years ago, Alan Turing published a seminal article , in which he proposed a simple reaction-diffusion model for pattern formation in biological systems. The basic idea is that there are two molecules (morphogens) that react with one another chemically and also diffuse through the system. The potential relevance of the model can be seen by comparing the lower panels below. The left panel is a real fish and the right panel shows the results of a simulation. The figure above is taken from a beautiful review article published a decade ago. Reaction-Diffusion Model as a Framework for Understanding Biological Pattern Formation   Shigeru Kondo and Takashi Miura The authors state that the model is not accepted by many experimental biologists and hope their review will lead to a greater engagement with it. Some of the reasons are related to issues in the philosophy of science and how to model complex systems. What is an explanation? What is the role of simple models for comple

 Until a few years ago I had never engaged with or received feedback from my writing from a professional editor. This is because the only genre I wrote that involved an editor was papers for scientific journals. But the editors of journals are not really editors in the literary sense. They are more like gatekeepers. Colleagues and collaborators may provide feedback on written work, but again they are amateurs. In the past few years, I have been writing some popular articles and a popular book and have been part of a writing group. In the process, I have engaged with several professional editors. They were getting paid to make my writing better. I have learnt a lot. Here are a few of the things. On the one hand, some of this may not seem that relevant to scientific articles and grant applications. On the other hand, think of the joy of reading a beautiful scientific article, such as those by Roald Hoffmann. Think of how many papers you try to read and you cannot figure out what they are

 I am at the beach this week and so a lot of time is spent staring at waves, clouds, sunsets, and patterns in the sand. There is a lot of beauty and a lot of beautiful science, most of which I know only a little about. For example, what is the essential physics and simplest theory that can explain the patterns below? To start understanding the beautiful patterns seen in natural systems I have found helpful the two-page Quick Study in Physics Today The universe in a cup of coffee  by John Wettlaufer Your morning java or tea is a rotating, cooling laboratory that reflects the physics of such large-scale phenomena as stellar dynamics and energy transport in Earth’s atmosphere and oceans.  A nice demonstration is to put the hot liquid in a glass jar and then just add a few drops of cold milk and see the beautiful patterns that emerge. The key idea is there is a balance between thermal bouyancy (hot air rises) and viscous stresses. This balance can lead to symmetry breaking and self-organis

Everyone likes to be right. But, sometimes I really wish I was wrong, particularly about problems I see in the world. I wish I was wrong about science being broken.  Some of these issues I discuss in the final chapter of Condensed Matter Physics: A Very Short Introduction , due to the relevance of these problems to the future of the field. Similar concerns were discussed with greater clarity, way back in 2014, by four scientists who are much more experienced and distinguished than I am.  Rescuing US biomedical research from its systemic flaws  Bruce Alberts , Marc W. Kirschner , Shirley Tilghman , and Harold Varmus Positions the different authors have held include President of the US Academy of Sciences, President of Princeton University, and Director of the National Institutes of Health. Although the article focuses on biomedical research I think the three words "medicine, biomedical, and biology" could be replaced respectively with "technology, materials science, and c

One of the most basic ideas in science is the controlled experiment. A single "independent" variable is changed while all others are held fixed. One then observes how the properties of the system change. Unfortunately, reality is more complicated and there are rarely any truly independent variables, particularly in materials science. Since the discovery of cuprate superconductors one-quarter of a century ago there has been a constant struggle to tease out systematic trends that can provide insight into the underlying physics causing the superconductivity. This is a challenge because it is difficult to change only one variable. For example, a key property is how the superconductivity changes with the chemical composition of the material, particularly with regard to the doping level, i.e., the density of charge carriers. The problem is that with changes in doping, many other things change as well: the amount of disorder, the periodicity and strength of magnetic interactions, cr

 A friend recently showed me that solid gallium can melt in your hand. I did not know this. I was quite familiar with liquid mercury, but not gallium.  The existence of elemental gallium was predicted by Mendeleev in 1869 after he constructed the periodic table. It was discovered within six years. He was able to predict that it would have a low-melting temperature, based on extrapolations from the known melting temperatures of elements close to it in the periodic table. Solid gallium is soft enough to be cut with a knife. Three different stable crystal structures for solid gallium are shown below. The phase diagram of pure gallium is shown below. Note the negative slope of the phase boundary between the liquid and the solid alpha-Ga. This is like water. It follows from the Clausius-Clapeyron equation that the solid state has lower density than the liquid state. Gallium is the only elemental metal with this property. (The semi-metals antinomy and bismuth also do). Gallium remains l

  I am currently working on the proofs and index for Condensed Matter Physics: A Very Short Introduction . It is wonderful to have got to this stage. It is slated for release on December 29. It can be pre-ordered from Oxford UP (GDP 9) , Amazon  (US $12), Book Depository  (US $16), ...

Significant understanding of emergent phenomena in quantum materials has come from the study of model Hamiltonians such as those associated with the names Hubbard, Anderson, Kondo, Heisenberg, Kitaev, Haldane, BCS,... I had not appreciated until recently that an early key to the Modern Synthesis of evolutionary biology (that brought together Darwinian natural selection with Mendelian genetics) was the development of simple mathematical models. The discussion below is taken from Towards a unified science of cultural evolution  Alex Mesoudi, Andrew Whiten and Kevin N. Laland  Significant advances were made in the study of biological [micro]evolution before its molecular basis was understood, in no small part through the use of simplified mathematical models, pioneered by Fisher (1930), Wright (1931), and J.B.S. Haldane (1932)...   Mathematical models such as [those for cultural evolution and gene-culture coevolution] are often treated with suspicion and even hostility by some social sc

The world is a mess. Most people want a better world. Sometimes nothing changes. Sometimes things change incredibly rapidly. Sometimes changes are positive. Other times the change is negative. Often this change is unanticipated, even by experts who have been studying the relevant topic for decades. Wicked problems are things that seem to be incredibly resilient to change. Examples of rapid changes that were (largely) positive and unanticipated were the peaceful collapse of the former Soviet empire, smoking in public becoming taboo, and increased public concern about climate change. Examples of negative changes include the rise of Trumpism, misinformation on social media, and the global financial crisis of 2008. Many people in government, public policy, NGOs, and social activists want to implement policies and take actions that will produce outcomes that (they believe) are positive. Here I discuss some basic but very important insights from "social physics", such as discussed

Condensed matter physics and sociology are both about emergence. Phenomena in sociology that are intellectually fascinating and important for public policy often involve qualitative change, tipping points, and collective effects. One example is how social networks influence individual choices, such as whether or not to get vaccinated. In my  previous post , I briefly introduced some Ising-type models that allow the investigation of fundamental questions in sociology. The main idea is to include heterogeneities and interactions in models of decision.  What follows is drawn from Sections 2 and 3 of the following paper from the Journal of Statistical Physics.  Crises and Collective Socio-Economic Phenomena: Simple Models and Challenges  by  Jean-Philippe Bouchaud Bouchaud first considers a homogeneous population which reaches an equilibrium state. This is then described by an Ising model with an interaction (between agents) J, in an external field, F that describes the incentive for the a