The Max Planck Institute for Dynamics and Self-Organisation

 
Here’s an entertaining thought experiment: what’s the difference between sand grains immersed in water and in air? The answer: absolutely nothing, except for the fluid – as Professor Stephan Herminghaus and his colleagues in Göttingen will tell you, they can both be treated as dry granular materials. There are no capillary forces and no liquid bridges between the grains in either case, and so the behaviour is essentially equivalent – and dramatically different from slightly wet sand - “soft matter” - where the capillary forces and bridges dominate the material’s character and allow, for example, the building of sandcastles.

I have just returned from an couple of days in Göttingen that included a visit to the Max Planck Institute for Dynamics and Self-Organization, a world-leading centre in research into the bizarre behaviours of granular materials, and of which Stephan is the Managing Director. But first, a brief explanation of why I was in Göttingen in the first place. Every year, the city hosts the Göttinger Literaturherbst, the autumn literary festival and, remarkably, I was invited to give a talk as part of the science strand of the event. The talk was last Saturday night and I was overwhelmed by the number of people who saw this as the way to spend a weekend evening. I was also more than overwhelmed by the venue. The Paulinerkirche, the church of Saints Peter and Paul, was built in 1304 and now forms part of the historical building compound of Göttingen State and University Library; it is a stunningly beautiful building:

 
At the far end of this picture is an exhibit case. And in there that evening was this:

 

Yes, the original 1610 edition of Galileo’s Sidereus Nuncius, the first scientific publication on observations through a telescope, describing the Milky Way, the moons of Jupiter, our Moon, and much more. This was almost too much. Göttingen is already awe-inspiring as you walk (extremely humbly) in the footsteps of Carl Friedrich Gauss, Ludwig Prandtl, Max Planck, Arthur Schopenhauer, Jon von Neumann, Max Born, David Hilbert, Werner Heisenberg, Bismarck, and the Brothers Grimm – to simply start the list. But I calmed myself down in the kind hands of Stephan Herminghaus as the moderator for the evening and launched into my German introduction. Not speaking German at all (except for greetings, thanks, and beer-ordering), and feeling the usual Anglophone guilt at the fluency of non-native-speakers, I had prepared some words of thanks and apology and employed my German brother-in-law to translate. After a lengthy phone audition with him, I then phoneticised the script and practiced diligently. The warm reception from the audience made it clear that this was going to be an enjoyable evening. This being a literary festival, I had prepared a talk that roamed from James Joyce to Australian aboriginal art via Rachel Carson, Jorges Luis Borges, and bacillus pasteurii – plus, of course, the wonders of granular materials. It was a great evening – a warm and enthusiastic audience, many questions, totally enjoyable.

The whole thing culminated in a book-signing session (always gratifying) and it was then that I met Matthias Schröter and Sibylle Nägle, who work in the Dynamics of Complex Fluids group at the Max Planck Institute. They asked if I would like a tour of the research labs the following day; I was obviously - and thankfully - unsuccessful at hiding my enthusiasm and protesting that the following day was Sunday and perhaps they had better things to do – we arranged to meet at the facility at 9.30 the following morning.

Now, much as I have been fascinated by the wonders of granular materials and much as I have written and talked about them, I had, until then, never had the privilege of actually seeing the work going on. We walked in and it was immediately seductive – it actually has that indefinable lab aroma. And it was, as is also typical, simple, almost garage-like, but, at the same time occasionally slightly chaotic; and, in every room, were very sophisticated pieces of kit designed, together with home-made apparatus, to investigate the complex behaviours of remarkably simple (apparently) materials. Here’s a vibrator (designed originally for shaking automobiles as part of the testing procedure, so this is a serious vibrator) that generates a model of the dynamics of a granular gas. The granular material in this case is comprised of rubber balls, a blur of frenzied activity that can be frozen momentarily by the camera flash.

 
One of the group’s primary quests is to better define the elusive but vital phase diagram for granular materials (see Matthias’s webpage on the topic) – Matthias patiently gave me a “granular phase diagrams for dummies” introduction to what he was working on:

 
Many of the research projects are simple but extremely clever. For example, while documenting the kinematic journeys of individual granular particles remains a challenge, the incredibly rapid changes in groups of moving particles can be tracked using the speckle patterns produced when the light from a laser responds to those changes – using a high-speed camera capable of seeing things going on far too rapidly for the human eye:

And then there is this, extremely impressive toy:

 
Borrowed from medical technology, this is an X-ray computed tomography unit: incredibly detailed 3-D imaging allows examination of granular packing structures, segregation, grain-to-grain interactions and much more. When we visited, the machine was in the middle of a run, but Matthias showed us movies of some initial trails that were amazing – including one of a sequence of images that allowed a student to decipher the combination of his bicycle lock that he had forgotten.

This is but a brief sampling of the kind of work that is going on in Stephan Herminghaus’s labs – my thanks again to all involved for making the weekend so memorable.

I’ll end with a couple of notes: first, in an environment under which UK scientific research is under threat of decimation, it was refreshing to find a country in which the critical contribution of fundamental science is still recognised and in which the necessary funding is available. Second, one of the questions I was asked after the talk was that, while it seems that granular materials research concentrates on using spherical grains of one sort or another, surely different shapes, different angularities are important? The answer is, of course, yes, nature rarely deals with perfect spheres, but even understanding the behaviours of perfect spheres remains a huge challenge and we can barely begin to deal with odd shapes – the exciting challenge of deceptively simple things.

And, finally, the superb buildings of old Göttingen are dominated by the beautiful hues and textures of the classic European Triassic - the Bunter Sandstone. Cross-bedded, of course:

[There’s a short film on YouTube of the work of Stephan and his colleagues – it’s in German, but the combined imagery of kids and cutting-edge physics is delightful in its own right. The image of sand-charged waves at the head of this post is from the DHD Multimedia gallery, Damon Hart-Davis]

Comments

[Jules]

Michael,

The link below is not exactly on the topic, but the mathmetician,Benoit Mandelbrot who coined the term fractals, died recently and his work explored the geometric patterns in nature that also include self-organzing properties. This is from the Earth Science Picture of the Day dated 10/24/2010 and has other links included to explore the topic of fractals and Mandelbrot

http://epod.usra.edu/

[Sandglass]

Thanks for the link, Jules - I think I'll be doing a post on Mandelbrot in the next few days, since I have a personal story related to him.