Issue 1, 2014

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Big Data Meets the Eye

Remember when a 20kB image took a minute to load? Back then, when dinosaurs were roaming the earth? Data has become big. Today we have more data than ever before, more data in fact than we know how to analyze or even handle. Big data is a big topic. Big data changes the way we do science and the way we think about science. Big data even led Chris Anderson to declare the End of Theory: “We can stop looking for models. We can analyze the......  [Read more]

Karl-Heinz Rädler Awarded the...

During their meeting on November 19th, members of the Astrophysics Group celebrated the award of this years Schwarzschild...

Solar Physics Research at Nordita

The latest of our videos about research and researchers at Nordita portrays our astrophysics group. Learn about the students'...

New Atom Accelerator to Date Human Bones

A new, highly advanced atom accelerator arrived in the beginning of December at the AMS 14C Dating Centre at Aarhus...

Cosmoparticle Breakthrough Awarded

The IceCube South Pole Neutrino Observatory was named the Physics World 2013 Breakthrough of the year, "for making the first...

PISA 2012: Swedish Schools in Decline

PISA, Program for International Student Assessment, is a triennial international survey commissioned by the OECD which aims to...


Big Data Meets the Eye

Remember when a 20kB image took a minute to load? Back then, when dinosaurs were roaming the earth?

Data has become big.

Today we have more data than ever before, more data in fact than we know how to analyze or even handle. Big data is a big topic. Big data changes the way we do science and the way we think about science. Big data even led Chris Anderson to declare the End of Theory:

“We can stop looking for models. We can analyze the data without hypotheses about what it might show. We can throw the numbers into the biggest computing clusters the world has ever seen and let statistical algorithms find patterns where science cannot.”

That was 5 years ago. Theory hasn’t ended yet and it’s unlikely to end anytime soon. Because there is slight problem with Anderson’s vision: One still needs the algorithm that is able to find patterns. And for that algorithm, one needs to know what one is looking for to begin with. But pattern finding algorithms for big data are difficult. One could say they are a science in themselves, so theory better not ends before having found them.

Those of us working on the phenomenology of quantum gravity would be happy if we had data at all, so I can’t say the big data problem is big on my mind, but I have a story to tell. Alexander Balatsky recently took on a professorship in condensed matter physics at Nordita, and he told me about a previous work of his that illustrates the challenge of big data in physics. It comes with an interesting lesson.

Electron conducting bands in crystals are impossible to calculate analytically except for very simplified approximations. Determining the behavior of electrons in crystals to high accuracy requires three-dimensional many-body calculations of multiple bands and their interactions. It produces a lot of data. Big data.

You can find and download some of that data in the 3D Fermi Surface Database. Let me just show you a random example example of Fermi surfaces, this one being for a gold-indium lattice:

The Fermi-surface roughly speaking tells you how electrons are packed. Pretty in a nerdy way, but what is the relevant information here?

The particular type of crystal Alexander and his collaborators, Hari Dahal and Athanasios Chantis, were interested in are so-called non-centrosymmetric crystals which have a relativistic spin-splitting of the conducting bands. This type of crystal symmetry exists in certain types of semiconductors and metals and plays a role in unconventional superconductivity that is still a theoretical challenge. Understanding the behavior of electrons in these crystals may hold the key to the production of novel materials.

The many-body, many-bands numerical simulation of the crystals produces a lot of numbers. You pipe them into a file, but now what? What really is it that you are looking for? What is relevant for the superconducting properties of the material? What pattern finding algorithm do you apply?

Let’s see...

Human eyes are remarkable
pattern search algorithms.
Image Source.

The human eye, and its software in the visual cortex, is remarkably good in finding patterns, so good in fact it frequently finds patterns where none exist. And so the big data algorithm is to visualize the data and let humans scrutinize it, giving them the possibility to interact with the data while studying it. This interaction might mean selecting different parameters, different axes, rotating in several dimensions, changing colors or markers, zooming in and out. The hardware for this visualization was provided by the Los Almos-Sandia Center for Integrated Nanotechnologies, VIZ@CINT; the software is called ParaView and shareware. Here, big data meets theory again.

Intrigued about how this works in practice, I talked to Hari and Athanasios the other day. Athanasios recalls:

“I was looking at the data before in conventional ways, [producing 2-dimensional cuts in the parameter space], and missed it. But in the 3-d visualization I immediately saw it. It took like 5 minutes. I looked at it and thought “Wow”. To see this in conventional ways, even if I had known what to look for, I would have had to do hundreds of plots.”

The irony being that I had no idea what he was talking about. Because all I had to look at was a (crappy print of) a 2-dimensional projection. “Yes,” Athanasios says, “It’s in the nature of the problem. It cannot be translated into paper.”

So I’ll give it a try, but don’t be disappointed if you don’t see too much in the image because that’s the reason d’être for interactive data visualization software.

3-d bandstructure of GaAs. Image credits: Athanasios Chantis.

The two horizontal axis in the figure show the momentum space of the electrons into the directions away from the high symmetry direction of the crystal. It has a periodic symmetry, so you’re actually seeing four times the same patch, and in the atomic lattice this pattern goes on to repeat. In the vertical direction, there are two different functions shown simultaneously. One is depicted with the height profile whose color code you see on the left and shows the energy of the electrons. The other function shown (rescaled) in the colored bullets, is the spin-splitting of three different conduction bands; you see them in (bright) red, white and pink. Towards the middle of the front, note the white band getting close to the pink one. They don’t cross, but instead they seem to repel and move apart again. This is called an anti-crossing.

The relevant feature in the data, the one that’s hard if not impossible to see in two dimensional projections, is that the energy peaks coincide with the location of these anti-crossings. This property of the conducting bands, caused by the spin-splitting in this type of non-centrosymmetric crystals, affects how electrons travel through the crystal, and in particular it affects how electrons can form pairs. Because of this, materials with an atomic lattice of this symmetry (or rather, absence of symmetry) should be unconventional superconductors. This theoretical prediction has meanwhile been tested experimentally by two independent groups. Both groups observed signs of unconventional pairing, confirming at a strong connection between noncentrosymmetry and unconventional superconductivity.

This isn’t the only dataset that Hari studied by way of interactive visualization, and not the only case where it wasn’t only helpful but necessary to extract scientific information. Another example is this analysis of a data set from the composition of the tip of a scanning tunnel microscope, as well as a few other projects he has worked on.

And so it looks to me that, at least for now, the best pattern-finding algorithm for these big data sets is the eye of a trained theoretical physicist. News about the death of theory, it seems, have been greatly exaggerated.

High Ranking of Nordic Universities in Physis

The 2013-2014 Times Higher Education World University Rankings has been recently released. Under the category "Physical Sciences" we find Nordic universities among the top 100 world class universities. Indeed, Stockholm University has been ranked 48, Lund University has been ranked 57, and University of Helsinki 63.

There are 13 parameters used for the rankings, grouped into five areas:

  • Teaching: the learning environment (worth 30% of the overall ranking score)
  • Research: volume, income and reputation (worth 30%)
  • Citations: research influence (worth 30%)
  • Industry income: innovation (worth 2.5%)
  • International outlook: staff, students and research (worth 7.5%)

[Read more...]

PISA 2012: Swedish Schools in Decline

PISA, Program for International Student Assessment, is a triennial international survey commissioned by the OECD which aims to evaluate education systems worldwide by testing the skills and knowledge of 15-year-old students in three key subjects: reading, mathematics and science. In PISA 2000 and 2003 Swedish 15-year-olds were ranked above the OECD average in all subjects, but over time Swedish results have dropped more than any other OECD country. In PISA 2012, the fifth PISA survey, 25 of 34 surveyed countries have a better result than Sweden in mathematics and science, and in reading 19 countries outrank Sweden, which is below the OECD average in all subjects.

The report has been widely discussed in Swedish media, with reactions ranging from calls to a complete emergency review of the Swedish school system, over blaming one's political opponents for the decline, to the Government's official position that there is nothing to worry about since reforms put in place last year will resolve any problems. One can expect education will be one of the hottest issues in the upcoming September 2014 elections.

Sources at OECD: PISA 2012 Results, PISA lessons. Read more: Swedish National Agency for Education press release (in Swedish).

Swedish Higher Physics Education Still Hanging On

The Swedish Higher Education Authority has finished evaluated all physics programs in Sweden, including the MSc in Engineering physics (civilingenjör i teknisk fysik) programs. Most engineering physics programs were evaluated to be of good or very good quality.

More information can be found at kvalitet.hsv.se/resultatsok where it is possible to search all subjects that has undergone review.

New Atom Accelerator to Date Human Bones

A new, highly advanced atom accelerator arrived in the beginning of December at the AMS 14C Dating Centre at Aarhus University, Denmark, replacing an old accelerator that broke down in 2010 in connection with renovations at the university. The primary task of the new atom accelerator will be to carry out accurate carbon-14 datings. For example, it only needs tiny samples in order to determine the exact age of ancient human bones, Iron Age spears, mammoth skeletons, Viking ships and a wide variety of other items.

The new technology can also be used on also be used to analyse samples to detect extremely rare isotopes from other substances. Determining the content of the Beryllium-10 isotope in ice core or sediment samples can, for instance, be used to chart the history of the Sun with a very high accuracy.

The new accelerator will be up and running within the next six months, as it takes some time to adjust and test the technology. [Read more...]

Cosmoparticle Breakthrough Awarded


The IceCube Lab in March, 2013. Image credit: IceCube Collaboration.

The IceCube South Pole Neutrino Observatory was named the Physics World 2013 Breakthrough of the year, "for making the first observations of high-energy cosmic neutrinos". Nordic partners in this world-wide scientific collaboration are the high-energy physics groups at Stockholm University and Uppsala University in Sweden, and NBI in Denmark.

NBI Constructs Quantum Information


The lab where the experiment was performed. Image credit: NIST.
Usually, when researchers work with quantum information, they do everything they can to prevent the information from decaying. Now researchers at the Quantum Optics Laboratory (QUANTOP) at the Niels Bohr Institute, have flipped things around and are exploiting the decay to create the entanglement of atomic systems, which is the foundation for quantum information processing. The research is a collaboration with the experimental research group lead by David Wineland (recipient of the Nobel Prize in physics last year) at the National Institute of Standards and Technology (NIST) in Boulder Colorado, USA, and has been published in Nature. [Read more...]

Practice, Not Innate Skill, Needed to Learn Maths

New research at the Norwegian University of Science and Technology (NTNU) in Trondheim could have an effect on how math is taught. If you want to be really good at all types of math, you need to practice them all. You can't trust your innate natural talent to do most of the job for you. This might seem obvious to some, but it goes against the traditional view that if you are good at math, it is a skill that you are simply born with. The results have been published in Psychological Reports. [Read more...]

Finns Have High Trust in Science

The results of the Finnish Science Barometer 2013 were published in November. The barometer polled Finns on their trust in science and scientific institutions. The quality and standard of science and research in Finland is deemed good, and the share of respondents who believe in the ability of science to produce reliable and accurate results is high. 70% are generally interested in scientific progress. Medical and environmental sciences were judged most interesting with around two thirds following them. The proportion of people interested in science has increased by 8% from the previous polling in 2010. The Finnish Science Barometer was commissioned by the Finnish Society for Scientific Information (Tieteen tiedotus). [Read more...]

Further Cuts to the University of Iceland

In an recent article in Fréttablaðið, the Rector of the university of Iceland, Kristin Ingólfsdóttir, reports further cuts on fundings reserved to the University of Iceland and to the School of Science in the 2014 budget. This is the 6th consecutive year that the University of Iceland and the Faculty of Science are facing this situation. The Rector has also pointed out that the amount of research grants to the university from national competitive funds have been substantially diminished.

To partially overcome these difficulties the Faculty of Science has placed great emphasis on applying for grants from international competitive funds. Moreover, also registry fees that students have to pay will be raised, but only a part of the increase returns directly to the University. [Read more... (in Icelandic)]

New Finnish Structural Policy Programme

On 29 November, the Finnish Government decided on the implementation of a structural policy programme. With respect to Universities a key goal of the programme is to speed up graduations. Among the tools to reach that will be:

  • Study grants for University students will be increased somewhat while the time one is eligible for that support is reduced
  • Funding of universities will become somewhat more dependent on the number of students who have studied more than 55 credits per year
  • Admittance of students into universities is temporarily increased, especially in those fields that are deemed more important by labor markets
  • Planning starts for enabling all year studying in universities

[Read more...]

IN BRIEF

Nobel Panel Discussion

Nobel panelists

During the hectic Nobel week, 2013 physics Nobel laureates François Englert and Peter Higgs visited AlbaNova (the campus where Nordita is situated). With characteristic wit and modesty they answered questions from the audience in a packed auditorium.

Later the same week, 2004 physics laureate Frank Wilczek presented the 2013 Oskar Klein Memorial Lecture entitled "Superfluidity and Symmetry Breaking: Past Glories, New Frontiers".

Swedish Grant Calls 2014

The Swedish research council (VR) has announced which calls will be available next year. Most grants calls are similar to last year with deadlines in March-April 2014, but one new grant appearing is an "International Career Grant" aimed at researchers 2-7 years after their PhD who wants to work abroad during a longer time period.



Norditians enjoying a traditional Swedish Christmas dinner in the Stockholm Archipelago.

Karl-Heinz Rädler Awarded the Schwarzschild Medal 2013

During their meeting on November 19th, members of the Astrophysics Group celebrated the award of this years Schwarzschild Medal to Karl-Heinz Rädler from the Leibniz-Institute for Astrophysics in Potsdam who is one of Nordita's frequent visitors. This medal is awarded annually by the German Astronomical Society to astronomers of highest scientific standing.

Karl-Heinz is one of the fathers of modern mean-field dynamo theory. In seminal papers between 1966 and 1969, he identified several effects that characterize the evolution of large-scale magnetic fields in cosmic bodies such as the Sun and other stars, planets, and even galaxies.

During the 1970s, he developed numerical approaches to compute global nonaxisymmetric mean-field models. Toward the end of the 1980s, he was allowed to travel from East Germany to the West and spent extended periods also in Helsinki, where he computed numerically the first nonlinear, nonaxisymmetric dynamo solutions that were relevant for explaining the magnetic fields in rapidly rotating stars. During the 1990s, acting as the founding director of the Astrophysical Institute Potsdam (now the Leibniz-Institute) he participated in preparatory calculations for the Karlsruhe dynamo experiment that demonstrated self-excited magnetic fields in helically flowing liquid sodium. In recent years, he developed a method for computing numerically turbulent transport coefficients from simulations. Much of his work has been instrumental for recent developments in the astrophysics group at Nordita.

During his last visit he computed analytic solutions to certain spatially periodic flow patterns called Roberts flows that we now understand as producing highly unconventional types of large-scale dynamos. In the picture, he explains striking properties of such flows that will be part of a new paper he is currently writing with members of the group at Nordita.

Members and visitors of the Nordita Astrophysics group, left to right: Bidya Binay Karak, Ebru Devlen, Anthony van Eysden, Sarah Jabbari, Nishant Singh, Matthias Rheinhardt, Illa R. Losada, Mikhail Modestov, Karl-Heinz Rädler, Elizabeth Cole, Dhruba Mitra, Lars Mattsson, Mikhail Liberman, and behind the camera Axel Brandenburg.

New Arrivals to Nordita

Postdoctoral Fellows

Nordita Fellow Lars Mattsson
Astrophysics

Lars received his PhD in 2009 from Uppsala University, under the supervision of Susanne Höfner, and later (in 2010) he joined the Dark Cosmology Centre at the Niels Bohr Institute, where he stayed for three years working in close collaboration with Anja C. Andersen. His main scientific interest is cosmic dust and his previous research has largely been about simulating dust formation together with dust-driven winds from carbon stars, and various aspects of the build-up of dust and related key-elements elements in galaxies. He joined the astrophysics group at Nordita in November 2013 as a postdoctoral fellow (Nordita fellow) and will work on physical modelling of cosmic-dust processing.

Solar Physics Research at Nordita

The latest of our videos about research and researchers at Nordita portrays our astrophysics group. Learn about the students' and postdocs' daily research life and hear Prof Axel Brandenburg explain some of the group's recent findings, solar weather and the formation of sun spots. Part of the movie was shot at the recent public outreach event "Physics in Kungsträdgården."

For more details about astrophysics at Nordita, see also Oliver's video and our recent feature article about the Sun's Butterfly Diagram.

For other video presentations of research at Nordita, see   www.nordita.org/video

From String Theory to Strange Metals

High temperature superconductors are badly understood theoretically, yet this understanding might allow us one day to create superconducting materials that save energy by avoiding resistive losses in long distance power lines. Imagine the potential! (Alternatively, read this.)

Presently the temperature at which these materials become superconducting is "high" only to the physicist who spends his days playing with liquid nitrogen: The transition temperature below which superconductivity sets in, also called the critical temperature, is in all known cases below -70°C. (The value depends on properties of the material as well as external fields.)

"Normal" superconductivity is described by the theory of Bardeen, Cooper and Schrieffer. At low temperatures, but in the not-superconducting phases, these metals are well described as Fermi liquids. But metals who display high temperature superconductivity are an entirely different story, and one that is largely unwritten.

One thing we know from experiment is that high temperature superconductors are "strange metals" whose electric resistance in the normal, non-superconducting, phase increases linearly with the temperature rather than with the square of the temperature. The latter is what one finds for a Fermi liquid with weakly coupled quasi-particles. Thus, plausibly the reason for our lacking theoretical understanding is that strange metals are strongly coupled system, which are notoriously hard to understand. "But darling," said the string theorist, "I can explain everything." And so he puts a black hole into an Anti-DeSitter (AdS) space and looks at the boundary.

The celebrated AdS/CFT correspondence makes it possible to deal with strongly coupled systems by mapping them to a weakly coupled gravitational system in a space-time with one more dimension. This is computationally more manageable, or at least one hopes so. So far, this correspondence, also called "duality", between the gravity in the AdS space and the strongly coupled theory on the boundary of this space (thus one dimension less) is an unproved conjecture put forward by Juan Maldacena. However, it has been extensively tested for a few cases and many people are confident that it captures a deep truth about nature (though they might disagree on the extent to which it holds).

For a high-temperature superconductor, one puts a planar black hole in the AdS space and decorates it with some U(1) vector fields and a scalar field, φ, and then goes on to calculate the free energy for different configurations of the scalar field. For temperatures above a critical value, the free energy is minimal if the scalar field vanishes identically. However, if the temperature drops below this critical value, configurations with a non-vanishing scalar field minimize the free energy, so the system must make a transition. In the figure below, you see the free energy, F, (with some normalization) as a function of the temperature (again with some normalization) for the case of φ = 0 (dotted line) and a case with non-vanishing φ (solid line). The latter solution doesn't exist for all values of the temperature. But note that when it exists, its free energy is lower than that of the φ=0 solution.

[Image credits: Hartnoll, Herzog and Horowitz]

For these different configurations one can then calculate thermodynamic quantities of interest, such as the electric conductivity (AC and DC) or heat conductivity, and… compare the results with actual measurements.

As you can tell already from my brief summary, this approach to understand strange metals is, presently, far too rough to give quantitative predictions. It can however describe qualitative behavior, such as the scaling of the resistance with temperature that is so puzzling. And that it does quite well!

A bunch of smart people have been studying the strange metal duals for a couple of years now, among others Subir Sachdev, Sean Hartnoll, Hong Liu (who wrote a recent article for Physics Today on the topic), Shamit Kachru, Gary Horowitz, and a group here at Nordita around Lárus Thorlacius.

Nordita Fellow Blaise Goutéraux is among the AdS/CFT correspondents of this group. He has taken on another challenge in this area, which is to describe the landscape of holographic quantum critical points, from which the strange metallic behavior at finite temperature is believed to originate. For this, Blaise works with more complicated geometries that exhibit different scaling behaviors from AdS.

What do we learn from this? The AdS/CFT correspondence is a tool, and if you've got a hammer quantum critical points start looking like nails. But the only reason we call the bulk theory gravitational is that we first encountered a theory of this type when we wanted to describe the gravitational interaction. Leaving aside this scientific history, in the end it's just a mathematical model to calculate observables that can be compared to experiment.

The big question is however whether this approach will ever be able to deliver quantitative predictions. For this, a connection would have to be made to the microscopic description of the material, a connection to the theories we already know. While this is not presently possible, one can hope that one day it will be. Then one could no longer think of the duality as merely useful computational tool with an educated guess for the geometry – the bulk theory would have to be a truly equivalent description for whatever is going on with the lattice of atoms on the boundary. But the cases for which the AdS/CFT correspondence has been well tested are very different from the ones that are being used here, and the connection to string theory, the original inspiration for the duality, has almost vanished. It wouldn't be the first time though that physicists' intuitions are ahead of formal proof.

UPCOMING SCIENTIFIC EVENTS

→ See List of all Nordita Events: www.nordita.org/events

Nordita Winter School 2014 in Condensed Matter Physics

School

6—17 January 2014

The aim of this research training course is to give to the participants an overview of current trends in condensed matter physics and at the same time provide them with the tools to enter into rapidly developing areas of research. The school is addressed to PhD students and young post-docs, and will last two weeks with 10 full days of teaching. As well as the basic topics fundamental to condensed matter physics, the school will cover the fields of magnetism, topological states of matter, and the physics of low-dimensional structures and interfaces.

Coordinators:  Eddy Ardonne, Stephen Powell, David Abergel, Alexander Balatsky

5th Nordic Workshop on Statistical Physics: Biological, Complex and Non-Equilibrium Systems

Workshop

26—28 March 2014

This workshop series provides a forum where scientists in the Nordic countries working in the area of Statistical Physics can meet regularly. Topics covered include diffusion problems, physics of DNA and bio-molecules, population dynamics, pattern formation, non-equilibrium transport, bacterial motility, single-molecule kinetics, dynamics and structure of networks, statistical inference, Monte-Carlo simulation techniques, self-assembly, soft condensed matter (colloids, liquid crystals etc.), work relations and fluctuation theorems, and many more.

Coordinators:  Alberto Imparato, Ralf Eichhorn

News in Neutrino Physics

Program

7 April — 2 May 2014

The focus of this program is the theory and phenomenology of neutrino physics and the role of neutrinos in astrophysics and cosmology. Important issues include extended versions of the Standard Model of particle physics including massive neutrinos, using neutrinos for probing astrophysical environments, and confronting theories with measurements. We intend the program to be a workshop in the real sense of the word, with informal discussion meetings and ample opportunities for research and discussion of common projects.

Coordinators:  Thomas Schwetz, Mattias Blennow, Tommy Ohlsson, Rikard Enberg

What is the Dark Matter

Program

5—30 May 2014

The nature of Dark Matter is one of the most important outstanding problems in modern physics. Many Dark Matter models exhibit high dimensional parameter spaces with many degeneracies and considerable expected backgrounds, and therefore a combination of all experimental data available will likely be necessary to arrive at robust conclusions regarding the nature of dark matter. The aim of the program is to bring together experimentalists, phenomenologists and theorists in order to discuss ideas, methods and models for interpreting the vast amount of data available.

Coordinators:  Lars Bergström, Timur Delahaye, Joakim Edsjö, Jan Conrad

Active Fluids: New Challenges from Experiments to High-Performance Computing

Workshop

28—31 May 2014

Recent years have been characterized by an increasing interest in and awareness of the role of multi-scale interactions in shaping the ecology of wide aquatic environments as the ocean and small-scale active suspensions as biofilms. Penetrating such a new and intriguing research field demands a multidisciplinary approach accounting for the coupling of physics, chemistry, and biology from the microscale to the macroscale.

Coordinators:  Dhrubaditya Mitra, Antti Puisto, Luca Brandt, Massimo Cencini, Guido Boffetta, Mikko Alava

Dynamics of Particles in Flows: Fundamentals and Applications

Program

2—27 June 2014

The question of the dynamics of particles in flows has a wide range of applications. Examples are the dispersion of pollutants in the atmosphere, fuel injection in a car engine, rain formation in clouds, and planet formation in circumstellar accretion disks. These examples have in common that the fundamental processes (collisions, coalescence, or breakup of particles) are determined by similar microscopic equations.

Coordinators:  Federico Toschi, Bernhard Mehlig, Dhrubaditya Mitra, Fredrik Lundell

OPEN POSITIONS AT NORDITA

→ See Current Open Postitions: www.nordita.org/positions

There are no open positions at the time of release of this issue of Nordita News.


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