Monday, November 12, 2018

Universality, probability, and the growth of rough surfaces

On Friday there was a nice UQ Maths and Physics Colloquium, Beyond the Gaussian Universality Class, given by Ivan Corwin,
The talk was a very nice example of synergy between fundamental physics and maths research.
There are interesting connections with simple one-dimensional models for surface growth, the Kardan-Parisi-Zhang equation, the KPZ universality class, traffic models, random matrix theory, directed polymers in random media, ....

Friday, November 9, 2018

Some hypotheses about universities

In the next month, I have been asked to give a talk and to write an article about universities in two different forums. What are universities for? How do they promote human flourishing?

Before I get too carried away I thought I would float a few ideas/claims/hypotheses that will be central to my argument that there needs to be a greater debate about fundamental issues and about the history of universities.

Some of the claims are interconnected.
In future posts, I may expand on some of these claims.

Universities are currently having a crisis of identity, mission, and purpose.

This crisis arises because there is a multitude of competing and conflicting visions from a range of "stakeholders".

This crisis and the degree of conflict is far greater and deeper than those faced by other institutions: government, schools, hospitals, business, charities, ...

Over time universities have been one of the most successful human institutions for promoting human flourishing (broadly defined) in many different ways: training leaders, science that produces useful technology, enriching cultural life, ...

Universities are a victim of their success.
Their current struggles follow the natural evolution of successful and growing organisations. 
Success increases the size, complexity, and cost of the organisation. Success also attracts "hangers on" who want a piece of the action: money, power, and social status. They do not have the same vision as the founders and first few generations of builders of the organisation. Their focus is more on their own agenda and interests than on the "common good" that the organisation originally sought to serve. This is a large part of the origin of the competing and conflicting visions.
Success also leads to the iron triangle of cost, access, and quality.

Here I expand on the first few claims.

Universities are currently having a crisis of identity, mission, and purpose.
I have written about this before. I think it is nicely illustrated by the diverse voices that claim this.

Universities on the Defensive 
Hunter Rawlings, a former President of Cornell, and currently the President of the Association of American Universities, a consortium of 60 of the leading North American universities.

The Slow Death of the University
Terry Eagleton, a distinguished literary critic, former Oxford Professor, and Marxist.

Higher Education is Drowning in BS,
by Christian Smith, a sociologist at the University of Notre Dame.



The crisis is not just about research universities in Western countries but also smaller teaching institutions and large state universities in the Majority World. Last year I was involved in a range of consultations run by a global NGO, identifying big issues in universities, and it was surprising how often this question, ``What is a university for?" came up.

This crisis arises because there is a multitude of competing and conflicting visions from a diverse range of "stakeholders".
The latter includes faculty, administrators, students, parents, alumni, future employers, politicians, taxpayers, funding agencies, donors, ...
The conflicting visions include neoliberalism, job training, a finishing school for the privileged, nation building, sectarian religious, social critique, scholarship, social transformation....

This crisis and the degree of conflict is far greater and deeper than those faced by other institutions.
One might argue that many public institutions (government, schools, hospitals, business, charities, ...) are currently in turmoil. However, most of these conflicts are about funding, governance, internal codes of conduct, and how to respond to rapid social and technological change. They are not conflicts about the primary purpose of the institution. One might also claim that as societies have become more multi-cultural, more politically divided, and complex this crisis just reflects, the many competing voices in the public square at large.
However, I would contend that universities are one of the most contested public institutions in society today. There are comparable debates about funding and access to health care. However, everyone agrees on the mission of hospitals: to help cure sick people. There is little debate about the goal, about the methodologies, or about the relative importance of different sub-fields of medicine. In contrast, in universities, there is significant contention about what the actual primary mission is and of the relative importance of different academic disciplines. No one proposes a large hospital without a pathology or oncology department. However, there are people who think humanities now have little to contribute to universities.

What do you think?
Which of my claims do you disagree with?

Monday, November 5, 2018

Bad metallic behaviour in ultracold atoms

There is a nice paper
Bad metallic transport in a cold atom Fermi-Hubbard system 
Peter T. Brown, Debayan Mitra, Elmer Guardado-Sanchez, Reza Nourafkan, Alexis Reymbaut, Simon Bergeron, A.-M. S. Tremblay, Jure Kokalj, David A. Huse, Peter Schaus, and Waseem S. Bakr

The paper represents a significant experimental advance in using ultracold atoms to investigate questions directly relevant to strongly correlated electron systems. In this case, the system Hamiltonian can be tuned to be a Hubbard model on a square lattice, such that the model parameters, U and t, and the doping, n are known.
One limitation is that current experiments can only be performed down to the lowest temperature of T/t =0.3. [For comparison, for cuprates this is of the order of 1000 K!].
Using imaging techniques the authors are able to directly extract the density (charge) diffusion constant D and the density susceptibility, chi, shown below. The experimental data are red dots. The blue curve is the result of calculations based on the Finite Temperature Lanczos Method (FTLM). Green dots the results of Dynamical Mean-Field theory. Gamma is the density relaxation rate.

Both the experiment and the ability to make such a detailed comparison with concrete theoretical calculations is a significant and exciting achievement.


The dashed curve in the upper panel is the value of the diffusion constant associated with the Mott-Ioffe-Regel limit below which one expects bad metal behaviour.
Aside: one should always keep in mind that for the MIR limit, different authors use different criteria, leading to different factors of pi, sqrt(pi), ...

Using the Nernst relation, sigma = chi * D,  the data above gives the conductivity (sigma) and resistivity (rho), shown below.
The blue and green curves correspond to the predictions, of FTLM and DMFT, respectively. The dashed grey line is the Mott-Ioffe-Regel limit.

One comment I have concerns an additional comparison that the authors could make. Based on heuristic arguments and results from AdS-CFT, Hartnoll conjectured a lower bound for the diffusion constant, hv_F^2/T.
Previously, Nandan Pakhira and I showed that this bound was significantly violated in the bad metallic regime, as described by DMFT.

There is also a commentary on the paper by Ehud Altman at the Journal Club of Condensed Matter.
I thank Matt Davis for bringing the paper to my attention.

Wednesday, October 31, 2018

Some basic ideas about teaching

Over the past few decades, I have taught a wide range of courses in diverse contexts. Perhaps I have been slow to learn how to be a better teacher. Since I began teaching things have changed dramatically. Our goals and the content of most curricula have changed little, and should not. However, advances in technology provide new opportunities but also challenges and potential distractions. The social context has changed significantly in terms of the expectations of both students and institutions.

Here are a few of the ideas that I think are important to keep in mind.  Some seem obvious, particularly in hindsight. On the other hand, practical implementations are a challenge. I think keeping the ideas in mind is also important for maintaining your sanity and motivation.
The ideas are listed in no particular order and many are interconnected.

The amount of learning that happens is correlated with the level of student engagement.
Engagement happens at many levels and in many ways: through attendance, listening carefully, taking notes, asking questions, reading texts, talking to classmates about content, working on problems, watching relevant videos, thinking about content, ...
Consequently, a good teacher explores strategies to increase student engagement. However, there is a limit to what you can do. This is why I despair of the situation in most beginning undergraduate classes in Australia. For example, in the last course that I taught there were about 100 students enrolled. Only about 30 actually showed up for class, and only about 20 used clickers in class to engage. Videos of the lectures are available (because of mandatory university policy), increasing the temptation of students to not attend. But most videos have viewed a handful of times. This is quite representative. It sadly contrasts to some different contexts I have taught where there is a very high level of student engagement.

The curriculum should be your servant not your master.
Textbooks get thicker and thicker with time. More and more content gets crammed into curricula. This increases the pressure to "cover material", even if students learn little. I recently had the opportunity to teach a whole course and took the liberty to reduce content and focus on depth of understanding. I think the outcomes were much better.

Accept and work with the hand of cards you that have been dealt.
We all have fantasies of teaching a class with students that are all gifted, well prepared, highly engaged, highly motivated, and appreciative. However, it never happens! We need to accept who they are, where they are at and adapt our expectations, strategies and academic level.

Flip, blend and mix the classroom.
On the one hand, there is a lot of hype about the value of "flipping the classroom",  online courses, and peer instruction. On the other hand, I am told (and I have my own anecdotal experience) that there is significant research that does show that a "blended" class [i.e. a combination of online and face-to-face] instruction is effective. I find that regular online quizzes and reflections do increase student engagement and give me helpful feedback about learning progress. But, expect some student resistance and complaints. If you reduce traditional lecturing a few students will complain that you aren't "teaching them" or that they are ``not getting their money's worth''!
Different students have different learning styles. Furthermore, today's students are more video oriented than text-oriented and have shorter attention spans. Hence, in a single class hour, there is value in a mixture of traditional lecture, short video clips, small group discussion, ...

Be mindful of the undercurrent of complex social and psychological dynamics in the classroom.
Students are human! They come to class with a lot of emotional and intellectual "baggage",  both good and bad: aspirations, gifts, expectations, insecurities, prejudices, excitement, preconceived ideas, fears, hopes, ...
Furthermore, they are not just individuals but a social unit. Your students have a relationship with you and with one another: positive, negative, ambivalent, or non-existent.
All this complex dynamics has the potential to enhance or to hinder learning. Unfortunately, much of it we have no control over. On the other hand, if we can discern some of the dynamics and respond appropriately it can enhance learning significantly.

Learning is enhanced through personal relationships.
Even extreme introverts are wired to be relational and yearn for meaningful relationships. They just want a few select relationships.

Accept that you will never make everyone happy.
It never ceases to amaze me how polarised student feedback and teaching evaluations are. You are the best/worst teacher they have ever had. This is the best/worse course they have taken. The course is too hard/easy... This is all for the same course and teacher! Don't take the feedback so personally.

What do you think?
Any other things that you think are important.

Wednesday, October 24, 2018

Advice for beginning bloggers

A friend asked me for any advice I have before he launches a blog. What mistakes have I made? How do I manage comments? What is the best platform?
So here are my rough thoughts.

Just do it!
This applies to both starting, persevering, and what you write. Blogging is not for perfectionists and procrastinators. A major strength (and weakness) of the medium is that one can float tentative and controversial ideas and not worry about endless editing and polishing. It can be an incredibly enriching experience, for both yourself and others.

The biggest impact of your blog may be on you not on your audience.
This is really true in my case. Blogging has clarified my thinking on a wide range of issues, from science to politics to religion.

Blogging saves time rather than taking time.

Don't be driven by metrics.
It is easy to keep track of page views and an abundance of other data. It is not clear how accurate or helpful it is. Furthermore, this can easily lead to feelings of insecurity and a temptation to write "click bait". I think the only really meaningful "metrics" are whether a post generates some useful discussion, someone learns something, or even changes their mind.

Go for the long haul.
Many people start blogs but quickly give up because they don't get much feedback. After about four years I was really wondering whether many people were reading this blog or whether it was having much impact. Then on an international trip, I kept meeting people who read it and thanked me for it. This provided motivation to keep going.

Most readers enjoy a diverse range of subjects.
That is the feedback I received from many readers, as I traverse from the technicalities of constructing diabatic states to mental health to teaching philosophy to ranting about metrics .... Obviously, some posts will be of more interest to some readers than to others. Don't worry about it.

Find ways to stimulate discussion in the comments section
This is probably my only regret. I was too slow to ask readers questions, to engage in discussion with commenters and to allow anonymous comments. On the one hand, I have not attracted as many comments as I would like. I am quite "jealous" of some of the discussions that people like Peter Woit, John Quiggin, and Peter Enns [there is an interesting mix of three people!] can generate. On the other hand, I have been blessed by the absence of trolls or the inane comments or abusive debates that seem so common on many blogs, youtube, and newspaper websites. The only comments I have felt the need to delete are spam advertising. But maybe I am not controversial enough to generate heated debate. One thing I do have to discipline myself is to not "name and shame" scientists and administrators that I think are charlatans. There are also certain topics I just avoid because it tragically seems almost impossible to have a civil online discussion and I am too scared of getting "condemned" for life for exploring some nuanced view that is "offensive", whether to people on the left or on the right.

Keep the software and formatting simple
There are endless possibilities for flashy formats. I am sticking with the most basic blogger.com format. There are plenty of popular and valuable blogs (e.g. John Quiggin and Peter Woit) that also use rudimentary formats. I suspect wordpress may be better than blogger.com because it does give more reliable and wider statistics.

Do readers or bloggers have other suggestions for someone about to start out?

Thursday, October 11, 2018

Key ideas in solid state physics

I have had some interesting discussions with an editor at Oxford University Press about the Very Short Introductions series. The upshot is that I have been asked to write a VSI Condensed Matter Physics. I find it amazing and concerning that after 500 titles there wasn't one about CMP. There are excellent ones on Magnetism, Superconductivity, Complexity, and Crystallography.
I am very happy about this and will post more about it later. At first, we discussed a VSI on Solid State Physics. Here is my outline for that.

1. Introduction
    Solid state physics
   - is central to technology (diodes, transistors, LEDs, photovoltaic cells, and computer memories)
   - provides important lessons in scientific model building
   - is one of the largest fields of physics
   - is a rich source of ideas and concepts that have cross-fertilised with other fields of science

2. Solids are quantum matter
Solids are made of atoms (nuclei and electrons).
Electrons are waves. Electrons are fermions. Quantum degeneracy
How is a metal like a white dwarf star?

3. Symmetry matters
Crystal structures. Think in reciprocal space, not in real space.
Why is it possible to determine a crystal structure from x-ray diffraction?
Internal symmetries of electrons: spin, gauge symmetries.

4. Electron waves in a crystal
Bragg scattering. Extended states.
Energy gaps: metals, semiconductors, and insulators
Why is copper a metal while diamond is an insulator?
Why can an electron go through a crystal and pass millions of atoms without being scattered?

5. Multitudes of solid phases
Phase diagrams. Allotropes.
When is graphite less stable than diamond?
Magnetic and superconducting phases
Classifications of phases through "broken symmetry"

6. Emergence
Quasi-particles: electrons and holes, phonons, magnons
How does structure (chemical and crystal) determines electronic and structural properties?
Why does magnesium seem to have positively charged electrical currents?

7. Beyond perfect infinite crystals
a. Impurities, disorder, localisation, glasses: the value of imperfection
b. Flatland. Surfaces and dimensionality

8. Topology matters
Quantum Hall effects, Topological insulators, Quantum magnetism

9. Solid state technology
 Diodes, transistors, LEDs, photovoltaic cells, and computer memories

10. Solid concepts
What have we learned about scientific model building?

This is too much. But what would you add or subtract?

Monday, September 24, 2018

A balanced response to dramatic change

There is no doubt that the world is changing very rapidly. This is true in many spheres: technology, politics, economics, and social. These changes present significant challenges to individuals, families, communities, businesses, institutions, and countries. On this blog there have been many posts and comments about how science and universities are changing.

I think there are three common mistakes in how people respond to these changes.

1. Denial. Claim that the changes are not really that significant (either qualitatively or quantitatively) and we should just keep on operating in the same way. This response will mostly come from those who are not directly affected in the short term.

2. On the other hand, some claim everything has changed and that everything is up for grabs, and they begin to lose sight of basic truths and goals, whether it is human aspirations or the content of physics curricula.

3. Seduction by the "change merchants." These are the opportunists: who want to use the change as a pretext to sell and implement their "solutions" from which they will increase their power, social status, or bank account.