Condensed concepts

Ben Powell and I have just advertised for a new postdoc position to work with us at the University of Queensland on strongly correlated electron systems. The full ad is here  and people should apply before January 28 through that link.

The Institute of Advanced Study at Durham University has organised a public lecture series, "The Future of the University." The motivation is worthy. In the face of this rapidly changing landscape, urging instant adaptive response, it is too easy to discount fundamental questions. What is the university now for? What is it, what can it be, what should it be? Are the visions of Humboldt and Newman still valid? If so, how? The poster is a bit bizarre. How should it be interpreted? Sadly, it is hard for me to even imagine such a public event happening in Australia. Last week one of the lectures was given by Peter Coveney ,  a theoretical chemist at University College London, on funding for science. His abstract is a bit of rant with some choice words. Funding of research in U.K. universities has been changed beyond recognition by the introduction of the so-called "full economic cost model". The net result of this has been the halving of the number of grant

Today I am giving a cake meeting talk about something a bit different. Over the past year or so I have tried to learn something about "complexity theory", including networks. Here is some of what I have learnt and found interesting. The most useful (i.e. accessible) article I found was a 2008 Physics Today article, The physics of networks by Mark Newman . The degree of a node , denoted k, is equal to the number of edges connected to that node. A useful quantity to describe real-world networks is the probability distribution P(k); i.e. if you pick a random node it gives the probability that the node has degree k. Analysis of data from a wide range of networks, from the internet to protein interaction networks, finds that this distribution has a power-law form, This holds over almost four orders of magnitude. This is known as a scale-free network , and the exponent is typically between 2 and 3. This power law is significant for several reasons. First, it is in

One of the biggest problems in theoretical physics is to explain why the cosmological constant has the value that it does. There are two aspects to the problem. The first problem is that the value is so small, 120 orders of magnitude smaller than what one estimates based on the quantum vacuum energy! The second problem is that the value seems to be finely tuned (to 120 significant figures!) to the value of the mass energy. The problems and proposed (unsuccessful) solutions are nicely reviewed in an article written in 2000 by Steven Weinberg. There seem to be four distinct responses to this problem. 1. Traditional scientific optimism. A yet to be discovered theory will explain all this. 2. Fatalism.  That is just the way things are. We will never understand it. 3. Teleology and Design. God made it this way. 4. The Multiverse . This finely tuned value is just an accident. Our universe is one of zillions possible. Each has different fundamental constants. It is is ama

Superconductivity is arguably the most intriguing example of emergent phenomena in condensed matter physics. The introduction to an endless stream of papers and grant applications mention this. But, so what? Why does this matter? Are we just invoking a "buzzword" or does looking at superconductivity in this way actually help our understanding? When we talk about emergence I think there are three intertwined aspects to consider: phenomena, concepts, and effective Hamiltonians. For example, for a superconductor, the emergent phenomena include zero electrical resistance, the Meissner effect, and the Josephson effect. In a type-II superconductor in an external magnetic field, there are also vortices and quantisation of the magnetic flux through each vortex. The main concept associated with the superconductivity is the spontaneously broken symmetry.  This is described by an order parameter. The figure below shows the different hierarchies of scale associated

It is now quite common for university management and funding agencies to run "consultations" where they interact with members of the "community" and "stakeholders". An example, I recently attended at my university was one concerning the university developing a "Mental Health Strategy". Some departments run "retreats" for staff members with similar aims. For reasons I describe below, I think such events vary greatly in their value and effectiveness. I write this because I would like to hear from readers what they think are important ingredients for an effective and meaningful consultation. My interest is partly because my wife and I were asked by a NGO and a philanthropic organisation to facilitate several consultations with a view to future grant-making initiatives. My literature search for "best practises" did not yield much. But here are two resources we did find helpful. How Employees Shaped Strategy at the New Yo

Today the Australian Medical Journal published an article Legal does not mean unaccountable: suing tobacco companies to recover health care costs  Ross MacKenzie, Eric LeGresley and Mike Daube This is getting some press and community attention. For the public record, I am not one of the authors. I am Ross McKenzie. Yesterday, I got an invitation to do an interview with a radio station in New Zealand! Now, I just received the following hate mail. Pity that you don't advocate for the government to recoup alcohol costs from companies, who have caused much more damage to drunks and others, you intellectual pigmy

1. Delegate 2. It can wait. These are also conducive to good mental health. The second is not a mandate for procrastination. Rather it is a mandate to be pro-active rather than reactive, to set and stick to priorities, to not let the squeaky wheel get the most oil, to let people solve their own problems,  .... I often feel pressure to get a long list of things done as soon as possible. This is not good for my stress level and mental health. However, if I can calm down and let things go, and come back to them later, I will have a better sense of perspective. I don't claim to have the best time management. Some earlier thoughts are here.

Different qualities are used to describe and characterise societies: civil, fair, intolerant, racist, corrupt, free,  …. Two big questions are: How does a society make a transition between from a bad quality and a good quality? What kind of initiatives can induce changes? Initiatives can be individual or collective, political or economic, local or national, ... For example, how does reduce corruption, which is endemic in many Majority world countries? Or in the USA, why is public debate losing civility? I think it is helpful to acknowledge the complexity of these issues. They have some similarity to wicked problems . They are problems that involve multiple interactions at multiple scales. Some of these interactions are competing and frustrated (in the spin glass sense!) and initiatives can lead to unintended consequences. Whether you look at societies from a sociological, cultural, geographical, political, or economic perspective they involve multiple scales. For example

Mental issues have been on my radar for the past few months, mainly for three reasons. First, I am coming back (very positively) from a low over the past year. Second, I continue to have many conversations with people who have struggled with the issue. Third, University of Queensland has decided to develop a "Mental Health Strategy" for students and staff. Last week I went to a public consultation about a draft document for UQ. (I was on leave from work, but thought it so important I went on campus). I read the document carefully, spoke out at the meeting, and also sent some email feedback. More on that later, maybe... Australian universities seem to have discovered the issue following the publication of a  report , concerning student mental health. The "strategy" for ANU is here. Here are a few valuable pieces that have "come across my desk" in the last few months. Santa Ono , President of the University of British Columbia, and a distinguished m

Think! Research is all about thinking about the world we live in; whether it is genetics, cosmology, literature, engineering, or economics, ... Reality is stratified and one observes different phenomena in different systems. As a result, one needs to think in distinct ways in order to develop concepts, laws, and methodologies for each stratum.  Note that thinking is central to experiments: thinking how to design the experiment and apparatus, and how to analyse the data produced and relate it to theory. This is why we have disciplines . Each discipline involves a disciplined way of thinking. Teaching is all about helping  students learn how to think. For specific disciplines, it involves learning how to think in a particular way. Thinking like a condensed matter physicist  is an art to learn. Similarly, thinking like an economist is a unique way of thinking. If this is the mission of modern universities are they successful? On one level they have been incredibly successf

How do complex structures emerge from simple systems? How do you define emergence? Conway's Game of life is a popular and widely studied version of cellular automata. It is based on four simple rules for the evolution of a two-dimensional grid of squares that can either be dead or alive. What is amazing is that distinct patterns: still lifes, oscillators, and spaceships can emerge. Gosper's glider gun  is shown below. What does this have to do with strongly correlated electron systems? The similarity is that one starts with extremely simple "rules" : a crystal structure plus Coloumb's law and the Schrodinger equation (Laughlin and Pines' Theory of Everything) and complex structures emerge: quasi-particles, broken symmetry states, topological order, non-Fermi liquids, ... Recently, Sophia Kivelson and Steven Kivelson [daughter and father] proposed the following definition: An emergent behavior of a physical system is a qualitative property that

Although this blog has a wide readership one thing it struggles with is to attract many comments, and particularly much back and forth discussion. Sometimes people tell me that this is just because it is not provocative or controversial enough. A while ago I changed the settings to allow anonymous comments and this has led to an increase in comments which is encouraging. However, I do have some ambivalence about this.  Ideally, any comment and opinion should be judged on the merits of its content not based on who is giving it. We should beware of arguments from authority. On the other hand, that is not the way most of us think and act. We do give some weight to the author. For example, an anonymous commenter says "I am a physicist and I am a climate change skeptic" it does not have the same weight as the opinion of a respected physicist who has relevant expertise. I am also concerned that people are not willing to take the risk of being publically identified with t

Australia has many unique things besides kangaroos and koalas. Long service leave  (LSL) is a generous and egalitarian feature of the "welfare" state. After ten years working for the same employer [or the same sector such as government universities] an employee is granted three months fully paid vacation. (The exact terms and conditions vary slightly between states and employers). LSL is available to all full-time employees, regardless of whether they are janitor or CEO. This is in addition to four (plus) weeks of annual leave and for faculty in addition to "sabbaticals" [called Special Studies Program in my university]. If an employee resigns any unused balance is "cashed out". University faculty work hard and some are workaholics. Many don't even take their allotted annual vacation, let alone LSL. Balances carry over each year and so some faculty have large balances. The "accountants" (who basically run the university) don't like t

I never thought I would write a blog post with such a word in it. In today’s Seattle Times there is an editorial about fake news and an opinion piece, How to fine-tune your BS meter, by Jevin West . At the University of Washington, West and Carl Bergstrom, have started a course entitled, Calling BS: Data reasoning for the digital age. West states: Our philosophy is that you don’t need a Ph.D. in statistics or computer science to call BS on the vast majority of data bullshit. If you think clearly about what might be wrong with the data someone is using and what might be wrong about the interpretation of their results, you’ll catch a huge fraction of the bullshit without ever going into the mathematical details.    Unfortunately, this applies to science as much as to Fake News. On his blog, Peter Woit discusses the rise of Fake Physics. Science is in trouble when the word I most often hear associated with the name of a particular Ivy League science Professor is BS. Furthermore

As part of a TV documentary, Why are we here ? produced by Ard Louis and David Malone there is a nice series of interviews where emergence is discussed by George Ellis , Peter Atkins , and Denis Noble. I can't seem to embed the interviews here and so have put in links to short clips. George Ellis discusses the difference between weak and strong emergence and his attitude to each. In separate clips, Denis Noble discusses emergence  and reductionism in biology. Peter Atkins, a hardcore reductionist, IMHO does not seem to seriously engage with the issue.

In 1935 Schrodinger wrote his famous paper (with the cat ) introducing the term entanglement, in response to the Einstein-Podolsky-Rosen paper published earlier that year. When Schrodinger wrote the paper he was living in a house on Northmoor Road , Oxford. This was the same house where Schrodinger learned he had been awarded the Nobel Prize. I recently learned some fascinating historical trivia. Schrodinger was a neighbour of J.R.R. Tolkien , who during that time was finishing up work on The Hobbit. It would be nice to see this landmark honoured, such as the one on Tolkien's house. However, it seems Schrodinger's house does not meet the criteria of  Oxfordshire Blue Plaques Board , because he lived there for three years, less than the required minimum of five years. Another option would be a plaque of the Institute of Physics, such as this one.

This is not based on the hubris of a condensed matter physicist, but rather the claim of three economists in an Econtalk  podcast ,  where  Don Boudreaux , Michael Munger , and Russ Roberts  discuss Emergent Order. For example, Boudreaux states the notion of spontaneous order is indeed the most profound, single most profound insight of good economics . It remains the insight that is most elusive to the general public. Sadly, it remains an insight that is elusive to a lot of professional economists these days. The discussion centres around Robert's poem, "Its a wonderful loaf" , the website for which has an animation of the poem and  a nice list of related resources . The key idea is that free markets lead to an emergent order of prices, division of labour, and matching of supply and demand. This order is Adam Smith's "invisible hand" that guides the economy. It is actually "bottom up", not top down. Many of the ideas discussed are those originat

I have received positive feedback about previous posts about mental health and so I share some recent experiences in the hope it may be helpful to some. I have had three significant times where my mental health deteriorated to the point I could not function “normally”. The first was during my Ph.D and the second about 15 years ago. The most recent experience was roughly six months ago. Here are a few things I learnt [or re-learnt] from this last experience. The decline is often gradual and not perceived or denied. It is like the proverbial frog in boiling water. It does not notice how the temperature is increasing and never jumps out. The longer you wait to address the issue the slower the recovery. Don't think things will get better on their own. Mental illness is irrational. That's the point. When I now think about some of the thoughts and perceptions that seemed “real” and “true” to me 6-12 months ago it is sad and bizarre. Relapse is not uncommon. If you have

I learned a lot from reading In the Eye of the Storm : The Autobiography of Sir John Houghton (with Gill Tavner). He is arguably best known for being the lead editor of the first three reports of the IPCC ( Intergovernmental Panel on Climate Change ). He started his scientific life as an atmospheric physicist at Oxford. Here are a few things that struck me. The value of development of new instruments. At Oxford Houghton was largely involved in finding new ways to use rocket based instruments measure the temperature and composition of the atmosphere at different heights. These were crucial for getting accurate data that revealed the extent of climate change and understanding climate dynamics. It was good for me to read this. As a theorist, I am often skeptical or at least unappreciative of the value of developing new instruments. I think it is partly because I have heard too many talks about instrument design where it really wasn't clear they were going to generate useful and re

Many of the most interesting materials involve significant chemical and structural complexity. Indeed, it is not unusual for a unit cell for a crystal to contain the order of one hundred atoms. Yet, for a given class of materials, one would like to find an effective Hamiltonian involving as few degrees of freedom and parameters as possible. Following Kino and Fukuyama, twenty years ago I argued that the simplest possible effective Hamiltonian for a large class of superconducting organic charge transfer salts was a one-band Hubbard model on an anisotropic triangular lattice at half filling. It seemed natural to then argue that the relevant model for the spin degrees of freedom in the Mott insulating phase is the corresponding frustrated Heisenberg model with spatial anisotropy determined by the anisotropy in the tight-binding model. However, it turns out this is not the case. There are some subtle quantum interference effects that I overlooked in the "derivation"  of t

Dimitri Mendeleev , who proposed the periodic table of the elements, purely from phenomenology and without quantum mechanics! He even successfully predicted the existence of new elements and their properties. A friend who is a high school teacher [but not a scientist] asked me about how he should teach the periodic table to chemistry students. It is something that students often memorise, especially in rote-learning cultures, but have little idea about what it means and represents. It makes logical sense, even without quantum mechanics. This video nicely captures both how brilliant Mendeleev was and the logic behind the table. A key idea is how each column contains elements with similar chemical and physical properties and that as one goes down the column there are systematic trends. It is good for students to see this with their own eyes. This video from the Royal Society of Chemistry shows in spectacular fashion how the alkali metals are all highly reactive and that as one g

In the book Who Got Einstein's Office? , about the Institute for Advanced Study at Princeton, the author Ed Regis, mocks it as the "One True Platonic Heaven" because he claims its members are Platonic idealists, who are interested in pure theory, and disdain such "impurities" as computers and applied mathematics. Platonic solids This stimulated me to think about the limited but useful role of pure mathematics, Platonic idealism, and aesthetics in solid state theory. People seem particularly excited when topology and/or geometry plays a role. The first example I could think of is the notion of a perfect crystal. Then comes Bloch's theorem, which surely is the central idea of introductory solid state physics. The icosahedron is central to quasi-crystals. Beautiful examples where advanced pure maths plays are role are Chern-Simons theory of edge states in the Quantum Hall Effect and topological terms in the action for quantum spin chains,

The picture below is of Godel's rotating universe . It represents an exact solution to Einstein's gravitational field equations and has the strange property of closed timelike curves (i.e. one can travel into the past!). This mathematical solution was found by Kurt Godel while he was employed by the Institute for Advanced Study at Princeton. I think I first encountered this picture in my final undergraduate year in the classic book, The Large Scale Structure of Space-Time by Hawking and Ellis, while working on a research project in general relativity. Godel's universe is just one example of the fascinating science and stories recounted in the book Who Got Einstein's Office? Eccentricity and Genius at the Institute for Advanced Study by Ed Regis , first published 30 years ago. I only read the book this past week and loved it. It is a captivating blend of science, mathematics, personalities, history, philosophy, humorous anecdotes, gossip, eccentricities ...

This is not about managing university endowments! On a recent flight I watched the fascinating HBO documentary, Becoming Warren Buffett. He may be one of the richest people in the world, and perhaps the most successful investor of all time. However, what is much more striking than his success is how he got there: in a completely counter-cultural (or iconoclastic) way. Here a few lessons that I think are particularly relevant to universities as they struggle with their identity, purpose, and management. Focus. Several times Buffett and some of his admirers emphasised this. Good research of companies and understanding the market requires considerable focus. You can't be doing lots of different things or jumping into the latest fad. Universities need to focus on teaching and research. Faculty need to focus on just a few things they can do well. The long view. Buffett does not "play" the market. He finds companies that are undervalued or have enduring market share

Last week at UQ we had a very nice mathematics colloquium , "Crowdsourcing mathematics problems" by Timothy Gowers. He first talked about the Polymath project , including its successes and marginal contributions. He then talked about a specific example of a project currently underway on his own blog , concerning transitive dice. This was pretty accessible to the general audience. This is where a well defined important problem is defined on a blog and then anyone is free to contribute to the discussion and solution. A strength of this approach is that it makes use of the complementary strengths, experience, and expertise of the participants. Specifically, solving problems includes: selecting a problem that is important, interesting, and potentially ripe for solution defining the problem clearly breaking the problem down into smaller parts including conjectures sketching a possible heuristic argument for the truth of the conjecture giving a rigorous proof of the conje

Some of my UQ colleagues and Jaime Merino have written a series of nice papers inspired by an organometallic molecular material Mo3S7(dmit)3. They have considered possible model effective Hamiltonians to describe it and the different ground states that arise depending on the model parameters. There is a rich interplay of strong correlations, Hund's rule coupling, spin frustration, spin-orbit coupling, flat bands, and Dirac cone physics. Possible ground states include some sort of Mott insulator, a Haldane phase, semi-metal, ... A good place to start is the following paper Low-energy effective theories of the two-thirds filled Hubbard model on the triangular necklace lattice  C. Janani, J. Merino, Ian P. McCulloch, and B. J. Powell The figure below (taken from this paper ) shows some of the molecular structure and some of the hopping integrals that are associated with an underlying decorated honeycomb lattice. This model could be called  kagomene,  because it interpol

I asked yesterday How would you respond to this email? I read it carefully and did not reply. The most striking thing was how generic it was. Although praising me and my work it never mentioned any specifics. Sometimes when I get student inquiries I send them an email similar to that below. Thanks for your interest. Please send me a copy of your CV and grade transcript. I suggest you look at my blog under the label “hydrogen bonds” or "strongly correlated electrons" to get some idea of my current interests. Also look at  “undergrads” and/or “Ph.D” to get some idea of my views and philosophy on supervision. I suggest after looking at the blog you then write and send me two paragraphs: one on why the science interests you and one on your perspective as to my philosophy. After that, if you are still interested I suggest we then meet in person. However, I did not send such an email for several reasons. I usually delete generic inquiries . If the student has not bothered t