Beats and Bounds: How Universal are the Properties of Time Series in Music?

As I discussed in a post a few weeks ago, we had the pleasure of hosting George Datseris, of the Max Planck Institute for Dynamics and Self-Organisation, last month. It’s taken a little while but there’s now video of George’s enthusiastic and thought-provoking talk…

Excitingly, my colleague Matt Brookes and his colleagues in the Sir Peter Mansfield Imaging Centre (SPMIC) here at Nottingham confirmed last week that Aerodrums can be used with the incredible brain imaging technology developed recently in the SPMIC; fortunately, the Aerodrums components don’t interfere with the image generation process.  Experiments along the lines of those sketched out towards the end of this post — and in collaboration with Esa Räsänen and George — are definitely on the horizon and I will blog about the results in due course.

“Some down-to-earth blue sky thinking”

“… a dangerous convergence proceeds apace 

as human beings confer life on machines and

in so doing diminish themselves. 

Your calculus may be greater than his calculus 

but will it pass the Sullenberger Hudson river test?”

from “Insulting Machines”, Mike Cooley

(Published in AI and Society 28 373 (2013))

Last week, I listened to some of the most thought-provoking — and occasionally unsettling — presentations and discussions that I’ve encountered throughout my academic career. On Tuesday, I attended, and participated in, the 2019 Responsible Research and Innovation Conference (organised by Nottingham’s Graduate School and the Institute for Science and Society), while on Wednesday the School of Physics and Astronomy hosted the British Pugwash Ethical Science half-day conference:

More on both of these soon. But before I describe just why I found those conferences as affecting as I did, I wanted to highlight last Monday’s session for the Politics, Perception, and Philosophy of Physics (PPP) module. This was the first of this year’s PPP sessions where the students were given free rein to contribute via debate and discussion, and both Omar Almaini (the co-convenor of PPP) and myself were exceptionally impressed by their thoughtful and spirited contributions. (The first three sessions of PPP are in the traditional lecture format. Sessions 4 – 11 are much more akin to the seminar style that is common in arts and humanities disciplines but is very much not the norm in physics courses.)

I have always found the clichés surrounding the STEM vs arts & humanities divide extremely tiresome, and it’s a delight when our students demolish the lazy stereotypes regarding the supposed lack of communication skills of physicists. (Similarly, one of the invited speakers for PPP this year, the sociologist Harry Collins, has shown that social scientists can perform comparably to – or even better than — physicists when it comes to answering physics questions. See “Sociologist Fools Physics Judges” (Nature, 2006) for compelling evidence. More from (and about) Prof. Collins in future posts…)

The title of last Monday’s PPP session was “The Appliance (and non-applicance) of Science” and the slides are embedded below. (Those of you who, like myself, are of a certain vintage might recognise the tag line of the title.)


The students drove an hour-long discussion that initially focussed on the two questions given on Slide #3 of the PowerPoint file above but rapidly diverged to cover key related points such as science comms, public engagement, hostility to expertise, and political polarisation. The discussion could have extended much beyond an hour — there were still hands being raised after we’d been in the seminar room for 90 minutes. As is traditional for PPP, I noted down students’ points and questions on the whiteboard as the discussion proceeded. Here are just two of the eight whiteboards’ worth of material…



(The remainder of the slides are available at the PPP website.)

In case you can’t read my appalling hand-writing, one of the first points raised by the students was the following:

“Curiosity is more than a valid reason to fund research” 

This view kicked off a lot of discussion, culminating in the polar opposite view expressed at the bottom of the whiteboard summary below: “What’s the point of funding anything other than global warming research?”


“Humanity came and destroyed the world”

The theme of the PPP session last Monday was chosen to align with the Responsible Research and Innovation (RRI2019) and Ethical Science conferences on the following days. This post would be 10,000 words long if I attempted to cover all of the key messages stemming from these conferences so I’ll focus on just a few highlights (out of very many). This story, by Dimitris Papadopoulos‘ daughter, was a sobering introduction to the motivations and agenda of RRI2019…

Dimitris was a driving force behind the organisation of RRI2019 (alongside colleagues in the Graduate School) and in his presentation he highlighted key aspects of the RRI framework that would recur time and again throughout the day: generational responsibility; designing for the future;  the realisation that what we create often has a lifespan far beyond our own; “the burden is not on the individual researcher” but we are collectively changing the planet.

He also stressed that, in his view, the primary task of science is not just to understand.

In the context of RRI I have a great deal of sympathy with Dimitris’ stance on this latter point. But I also found it rather unsettling because science that is as disinterested as possible and focussed solely on understanding the nature of the world/universe around us has to be a component of the research “landscape”, not least because, time and again throughout history, curiosity-driven science has led to truly disruptive innovations. (Some to the immense benefit of humanity; others less so, admittedly.) Moreover, we need to be exceptionally careful to retain the disinterested character of pure scientific research when it comes to ensuring public trust in just what we do — an issue to which I returned in another RRI2019 session (see below).

Prof. Sarah Sharples, PVC for Diversity, Equality, and Inclusion, was next to speak and made powerful and pointed arguments that senior university (and, indeed, University) management, politicians, and funding bodies of all stripes need to take on board: look beyond simplistic metrics and league tables when it comes to assessing what it means for research to be successful. Sarah highlighted the importance of unintended consequences, particularly when it comes to the ironies of automation; clinical care, in particular, is not just about recording numbers and data.


Pete Licence, Professor of Chemistry and Director of The GlaxoSmithKline Carbon Neutral Laboratory, continued on the theme of being wary and cognisant of the possibility and potential of unintended consequences, but stressed that sometimes those consequences can be much more positive than we could have ever anticipated. Pete described his collaboration with a number of Ethiopian scientists, which has radically changed both his and their approach to not just the science but the economics associated with green chemistry. He also echoed Sarah Sharples’ key point on the matter of ensuring that we never lose sight of the humanity behind the metrics and tick-boxes: too many lenses mean that, paradoxically, we can often lose focus…

Maybe, Minister?

The RRI conference then split into parallel sessions. This unfortunately meant that I couldn’t go along to the Society and Responsibility discussion — which I was keen to attend (not least because my friend and colleague Brigitte Nerlich was a member of the panel) – as I was participating in the Responsibility in Research and Policy session happening at the same time, alongside Chris Sims (Head of Global Policy Impact at UoN and the Chair and organiser of the session), Steven Hill (Director of Research at Research England, and formerly Head of Policy at HEFCE), and Richard Masterman, UoN’s Associate PVC for Research Strategy and Performance. (All-male panels are never a good look but, in the organisers’ defence, the panel was not initially male only — the original speaker, Dr. Karen Salt (Director of the Centre for Research in Race and Rights at UoN), unfortunately couldn’t make it — and the parallel Society and Responsibility session involved an all-female panel.)

Steven and I have debated and discussed the issues surrounding HEFCE’s, and the research councils’, approach to research impact on a number of occasions — some more heated than others — over the years. (I was very pleased to find that we seem to have converged (give or take) on the middle ground after all these years.) After Chris framed the key themes of the panel discussion, we each had approximately ten mins to make our case. Steven’s ccontribution focussed on the core issue of just how research should (or should not) inform policy and just what RRI should look like in that “space”.

The trade-offs and tensions between researchers and politicians were a core theme of Steven’s argument. To a scientist, the answer to any question is invariably “More research is needed”; a politican, on the other hand, ideally has to make a decision, sometimes urgently, on the basis of the evidence at hand. And the last thing they want to be told is that more research is needed. This was also the resounding message I got at Westminster when I participated (along with my Physics & Astronomy colleague Clare Burrage) in the Royal Society’s MP-Scientist scheme back in 2013: science really is not as far up the pecking order as we scientists might like. For this reason, I enthusiastically recommend Chris Tyler‘s illuminating “Top 20 things scientists need to know about policy-making” to the PPP class every year.

Steven mentioned Roger Pielke Jr’s “honest broker” concept — whereby scientists should be entirely disinterested, fully objective reporters of “The Truth” (however that might be defined) when interacting with politicians and policy. In other words, any tendency towards activism — i.e. promoting a particular (geo)political standpoint — should be avoided entirely. I have major qualms with Pielke’s thesis but Ken Rice (aka “…And Then There’s Physics“) has dealt with these much more comprehensively and eloquently than I could ever manage.

I was also put in mind, on more than one occasion during Steven’s presentation, of “The Thick Of It” clip below (which also features in the PPP course each year. Apologies for the audio quality.)

Richard then outlined the University of Nottingham’s views on the policy-research interface, before I presented the following [1]:


The ensuing discussion amongst the panel members, with a lively Q&A from the floor, touched on many of the same points that had been raised during the PPP session the day before: the disinterestedness of research, basic vs applied science, polarisation in politics, trust in scientists (and other professions), the commercialisation of academic research (which was the subject of a particularly pointed question from Jane Calvert in the audience – more on whom below), and balancing public, political, academic, and commercial drivers.

Synthetic Aesthetics and The Wickedness of Global Challenges

In the first session after lunch, the aforementioned Prof. Calvert, of the School of Social and Political Science at Edinburgh, presented an enthralling keynote lecture entitled Responsible Innovation and Experimental Collaboration, in which se described her adventures in synthetic biology, with a particular focus on cross-disciplinary interactions between artists, scientists (of both the social and life variety), and designers.


A particularly fascinating aspect of Prof. Calvert’s talk was the description of her work on the Synthetic Aesthetics project, from which a book (among many other “outputs”) has stemmed. I’ll quote directly from the blurb for the book because it captures the core message of Jane’s talk:

In this book, synthetic biologists, artists, designers, and social scientists investigate synthetic biology and design. After chapters that introduce the science and set the terms of the discussion, the book follows six boundary-crossing collaborations between artists and designers and synthetic biologists from around the world, helping us understand what it might mean to ‘design nature.’ These collaborations have resulted in biological computers that calculate form; speculative packaging that builds its own contents; algae that feeds on circuit boards; and a sampling of human cheeses. They raise intriguing questions about the scientific process, the delegation of creativity, our relationship to designed matter, and, the importance of critical engagement. Should these projects be considered art, design, synthetic biology, or something else altogether?

I have a long-standing interest in the interface between the arts and the sciences — see, for example, The Silent Poetry of Paint Drying, and these posts — so was fascinated by the interweaving of function, form, and, errmm, fungi in the Synthetic Aesthetics project…


The second post-lunch keynote was from Prof. Phil McNaghten (Wageningen University & Research (WUR), Netherlands), whose work with Matthew Kearnes and James Wilsdon on the ESRC-funded “Governing At The Nanoscale: People, Policies, and Emerging Technologies” project (published in this Demos pamphlet) was more than partly responsible for sparking my nascent interest in the sociology of (nano)science and technology more than a decade ago. Phil’s talk at RRI2019 focussed on how RRI was embedded in practice and policy at the local (WUR), national (EPSRC), and international (Brazil, which is enduring vicious cuts to its science budget) levels.

The Sounds of (Responsible) Salesmen…

I unfortunately only caught the last fifteen minutes or so of the Molecules and Microbes parallel session — chaired by Pete Licence and featuring Prof Steve Howdle (Chemistry, Nottingham), Prof Liz Sockett & Dr Jess Tyson (Life Sciences, Nottingham), and Prof Panos Soultanas (Chemistry, Nottingham) — and so can’t really comment in detail. Panos’ impassioned plea for support for basic, curiosity-driven science certainly resonated, although I can’t say I entirely agreed with his suggestion that irresponsible research wasn’t an issue. (I may have misinterpreted what he meant, however — I didn’t catch all of his presentation.)

The closing plenary was expertly chaired by Dr. Alison Mohr, who introduced, in turn, Dr. Eleanor Kershaw (Synthetic Biology Centre, UoN), Prof. Richard Jones (Physics, University of Sheffield (and erstwhile PVC for Research and Innovation there), and Prof. Martyn Poliakoff. I have known Richard for over fifteen years and have always enjoyed his informed and engaging takes on everything from nanotechnology to transhumanism to the UK’s productivity crisis, via a variety of talks I’ve attended and his blog, Soft Machines. (I also had the pleasure of spending a week at an EPSRC sandpit back in 2007 that was coordinated and steered — in so far as it’s possible to steer a room-full of academics — by Prof. Jones.)

In his plenary, Richard stressed the “scientist as responsible salesman” theme that he has put forward previously (as one of many dimensions of responsibility.) For a characteristically comprehensive analysis of responsible innovation (and irresponsible stagnation), I thoroughly recommend this Soft Machines post.

Martyn Poliakoff brought the conference to a close in his ever-engaging and inimitable style, with a compelling vision of what he and his colleagues have described as a Moore’s law for chemistry,

… namely that over a given period, say five years, sustainable chemists should strive to reduce the amount of a chemical needed to produce a given effect by a factor of two and this process should be repeated for a number of cycles. The key will be to make the whole concept, especially the economics, work for everyone which will require a change in business model for the chemicals market.

[Quote taken from A New Approach to Sustainability: A Moore’s Law for Chemistry, M. Poliakoff, P. Licence, and M. George, Angew. Chem. Int. Ed. 57 12590 (2018)]

“Remember your humanity, and forget the rest.”

Although the word Pugwash has an alternative “resonance” for many of us kids of the sixties/seventies, the Pugwash Conferences on Science and World Affairs, and the subsequent International Student/Young Pugwash movement, take their name from the town in Nova Scotia, Canada where Joseph Roblat and Bertrand Russell established, in 1957, the international organisation to bring together scientists and public figures to address global security, armed conflict, and the threat of weapons of mass destruction (including, in particular, nuclear warfare). The Pugwash conferences were initiated two years after the Russell-Einstein manifesto was issued, which in turn stemmed from Russell’s deep fears about atomic weapons:

The prospect for the human race is sombre beyond all precedent. Mankind are faced with a clear-cut alternative: either we shall all perish, or we shall have to acquire some slight degree of common sense. A great deal of new political thinking will be necessary if utter disaster is to be averted.

Jo(seph) Roblat was awarded the Nobel Peace Prize in 1995 “for efforts to diminish the part played by nuclear arms in international affairs and, in the longer run, to eliminate such arms.” 

I have organised a number of joint events with British Pugwash — more specifically, with Andrew Gibson, the British Pugwash Student Manager — over the last few years, including a PPP seminar given back in Nov. 2016 by Prof. John Finney (UCL), Pugwash Trustee, and a tireless advocate for the organisation. Alongside Peter Jenkins, Chair of British Pugwash, John kicked off the Ethical Science conference at Nottingham last Wednesday with a fascinating account of the history of Pugwash and, in particular, Jo Rotblat’s inspiring life.


Dr. Ian Crossland then discussed the ethics and intergenerational issues surrounding nuclear power, followed by a stirring presentation by Sam Harris, climate activist and Nottingham Trent Labour Society’s campaigns officer, on Labour’s Green New Deal.

LauraNolan.pngA  particular highlight of not just the Pugwash conference but of all of last weeks’ events was Laura Nolan‘s remarkable presentation, delivered with tons of energy and passion. (I try to avoid the p-word, given that it’s an obnoxiously lazy cliche, but in this case it is more than justified.) Laura, a Trinity College Dublin computer science graduate, resigned from Google, where she was a software engineer, in 2017 after she was asked to work on a project whose focus was the enhancement of US miltary drone technology. Laura’s story is recounted in this important Guardian article. (See also this interview.) The quote below, from that article, captures the issues that Laura covered in her talk at the Pugwash conference.

“If you are testing a machine that is making its own decisions about the world around it then it has to be in real time. Besides, how do you train a system that runs solely on software how to detect subtle human behaviour or discern the difference between hunters and insurgents? How does the killing machine out there on its own flying about distinguish between the 18-year-old combatant and the 18-year-old who is hunting for rabbits?

Anuradha Damale — currently of Verification Research, Training and Information Centre, and a fellow physicist — had a tough act to follow but she delivered a great talk with quite some aplomb, despite having lost her voice! Anuradha covered the troublesome issue of nuclear weapons verification programmes, and despite the lack of vocal volume, participated in a lively Q&A session with Laura following their talks.

I’m going to close this post with the source of its title: “Down-to-earth blue sky thinking”. The inspiring video embedded below was shown by Tony Simpson — who also discussed Mike Cooley’s pioneering work on the influence of technology on society (and whose prose poem, “Insulting Machines“, is quoted above) — during the closing presentation of the Pugwash conference.

I’ve waffled on for much too long at this point. Let’s hear instead from those whose actions spoke so much louder than words…



[1] It’s unfortunately not clear from the embedded SlideShare widget of the slides but I cited (and quoted from) this influential blog post when crediting Gemma Derrick and Paul Benneworth with coining the “grimpact” term.

Josephine Draws

A quick post to mention another example of physics-art crossover, this time to highlight the incredible artistic talent of Jo Melton, who graduated from Nottingham with a thoroughly well-deserved 1st class hons MSci in Physics degree earlier this year. Jo has recently set up her own art business:

A few years back I asked Jo if she could do a drawing of Daisy, our miniature dachshund, for my daughter Saoirse’s tenth birthday. Here’s the photo of Daisy I gave Jo…


…and here’s Jo’s drawing (sans whiskers, which were added in later):


Impressive, right?

As you might expect, Jo isn’t limited to drawing dogs…


More examples of Jo’s artwork can be found at her Instagram page, @instagramdraws_x. If, unlike myself, you’re on Instagram, follow Jo!

Does art compute?

A decade ago, a number of physicists and astronomers, an occasional mathematician, and even an interloping engineer or two (shhh…) here at the University of Nottingham started to collaborate with the powerhouse of pop sci (/pop math/pop comp/pop phil…) videography that is Brady Haran. I was among the “early adopters” (after the UoN chemists had kicked everything off with PeriodicVideos) and contributed to the very first Sixty Symbols video, uploaded back in March 2009. This opened with the fresh-faced and ever-engaging Mike Merrifield: Speed of Light.

Since then, I have thoroughly enjoyed working with Brady and colleagues on 60 or so Sixty Symbols videos. (Watching my hairline proceed backwards and upwards at an exponentially increasing rate from video to video has been a somewhat less edifying experience.) More recently, I’ve dipped my toes into Computerphile territory, collaborating with the prolific Sean Riley — whom I first met here, and then subsequently spent a week with in Ethiopia — on a number of videos exploring the links between physics and computing.

It’s this ability to reach out to audiences other than physicists and self-confessed science geeks that keeps me coming back to YouTube, despite its many deficiencies and problems (such as those described here, here, and here. And here, here, and here [1].) Nonetheless, during discussions with my colleagues about the ups and downs of online engagement, I’m always tediously keen to highlight that the medium of YouTube allows us to get beyond preaching to the converted.

Traditional public engagement and outreach events are usually targeted at, and attract, audiences who already have an interest in, or indeed passion for, science (and, more broadly, STEM subjects in general [2].) But with YT,  and despite the best efforts of its hyperactive recommendation algorithms to corral viewers into homogeneous groupings (or direct them towards more and more extreme content), it’s possible to connect with audiences that may well feel that science or math(s) is never going to be for them, i.e. audiences that might never consider attending a traditional science public engagement event. The comment below, kindly left below a Numberphile video that crossed the music-maths divide, is exactly what I’m talking about…


There’s still a strong tendency for a certain type of viewer, however, to want their content neatly subdivided and packaged in boxes labelled “Physics”, “Chemistry”, “Biology”, “Philosophy”, “Computing”, “Arts and Humanities Stuff I’d Rather Avoid” etc… Over the years, there have been comments (at various levels of tetchiness) left under Sixty Symbols, Periodic Videos, Computerphile etc… uploads telling us that the video should be on a different channel or that the content doesn’t fit. I hesitate to use the lazy echo chamber cliché, but the reluctance to countenance concepts that don’t fit with a blinkered view of a subject is not just frustrating, it narrows the possibilities for truly innovative thinking that redefines — or, at best, removes — those interdisciplinary boundaries.

Some physicists have a reputation for being just a little “sniffy” about other fields of study. This was best captured, as is so often the case, by Randall Munroe:

But this is a problem beyond intellectual arrogance; a little learning is a dangerous thing. As neatly lampooned in that xkcd cartoon, it’s not just physicists who fail to appreciate the bigger picture (although there does seem to be a greater propensity for that attitude in my discipline.) A lack of appreciation for the complexity of fields that are not our own can often lead to an entirely unwarranted hubris that, in turn, tends to foster exceptionally simplistic and flawed thinking. And before you know it, you’re claiming that lobsters hold the secret to life, the universe, and everything…

That’s why it’s not just fun to cut across interdisciplinary divides; it’s essential. It broadens our horizons and opens up new ways of thinking. This is particularly the case when it comes to the arts-science divide, which is why I was keen to work with Sean on this very recent Computerphile video:

The video stems from the Creative Reactions collaboration described in a previous post, but extends the physics-art interface discussed there to encompass computing. [Update 08/06/2019 — It’s been fun reading the comments under that video and noting how many back up exactly the points made above about the unwillingness of some to broaden their horizons.] As the title of this post asks, can art compute? Can a painting or a pattern process information? Can artwork solve a computational problem?

Amazingly, yes.

This type of approach to information processing is generally known as unconventional computing, but arguably a better, although contentious, term is lateral computing (echoing lateral thinking.) The aim is not to “beat” traditional silicon-based devices in terms of processing speed, complexity, or density of bits. Instead, we think about computing in a radically different way — as the “output” of physical and chemical and/or biological processes, rather than as an algorithmic, deterministic, rule-based approach to solving a computational problem. Lateral computing often means extracting the most benefit from analogies rather than algorithms.

Around about the time I started working with Brady on Sixty Symbols, our group was actively collaborating with Natalio Krasnogor and his team — who were then in the School of Computer Science here at Nottingham — on computational methods to classify and characterise scanning probe images. Back then we were using genetic algorithms (see here and here, for example); more recently, deep learning methods have been shown to do a phenomenally good job of interpreting scanning probe images, as discussed in this Computerphile video and this arXiv paper. Nat and I had a common interest, in common with quite a few other physicists and computer scientists out there, in exploring the extent to which self-assembly and self-organisation in nature could be exploited for computing. (Nat moved to Newcastle University not too long afterwards. I miss our long chats over coffee about, for one, just how we might implement Conway’s Game Of Life on a molecule-by-molecule basis…)

It is with considerable guilt and embarrassment that I’ve got to admit that on my shelves I’ve still got one of Nat’s books that he kindly lent to me all of those years ago. (I’m so sorry, Nat. As soon as I finish writing this, I’m going to post the book to you.)

This book, Reaction-Diffusion Computers by Andy Adamatzky, Ben De Lacy Costello, and Tetsuya Asai, is a fascinating and comprehensive discussion of how chemical reactions — in particular, the truly remarkable BZ reaction — can be exploited in computing. I hope that we’ll be able to return to the BZ theme in future Computerphile videos. But it was Chapter 2 of Adamatzky’s book, namely “Geometrical Computation: Voronoi Diagram and Skeleton” — alongside Philip Ball’s timeless classic, The Self-Made Tapestry (which has been essential reading for many researchers in our group over the years, including yours truly) — that directly inspired the Computerphile video embedded above.

The Voronoi diagram (also called the Voronoi tesselation) is a problem in computational geometry that crops up time and again in so very many different disciplines and applications, spanning  areas as diverse as astronomy, cancer treatment, urban planning (including deciding the locations of schools, post offices, and hospital services), and, as discussed in that video above, nanoscience.

We’ve calculated Voronoi tesselations extensively over the years to classify the patterns formed by drying droplets of nanoparticle solutions. (My colleagues Ellie Frampton and Alex Saywell have more recently been classifying and quantifying molecular self-assembly using the Voronoi approach.) But Voronoi tesselations are also regularly used by astronomers to characterise the distribution of galaxies on length scales that are roughly ~ 1,000,000,000,000,000,000,000,000,000,000 (i.e. about 1030) times larger than those explored in nanoscience. I love that the same analysis technique is exploited to analyse our universe on such vastly different scales (and gained a lot from conversations with the astronomer Peter Coles on this topic when he was a colleague here at Nottingham. )

As Cory Simon explains so well in his “Voronoi cookies and the post office problem” post, the Voronoi algorithm is an easy-to-understand method in computational geometry, especially in two dimensions: take a point, join it up to its nearest neighbours, and get the perpendicular bisectors of those lines. The intersections of the bisectors define a Voronoi cell. If the points form an ordered mesh on the plane — as, for example, in the context of the atoms on a crystal plane in solid state physics — then the Voronoi cell is called a Wigner-Seitz unit cell. (As an undergrad, I didn’t realise that the Wigner-Seitz unit cells I studied in my solid state lectures were part of the much broader Voronoi class — another example of limiting thinking due to disciplinary boundaries.)

For less ordered distributions of points, the tesselation becomes a set of polygons…


We can write an algorithm that computes the Voronoi tesselation for those points, or we can stand back and let nature do the job for us. Here’s a Voronoi tesselation based on the distribution of points above which has been “computed” by simply letting the physics and chemistry run their course…


That’s an atomic force microscope image of the Voronoi tesselation produced by gold nanoparticles aggregating during the drying of the solvent in which they’re suspended. Holes appear in the solvent-nanoparticle film via any (or all) of a number of mechanisms including random nucleation (a little like how bubbles form in boiling water), phase separation (of the solid nanoparticles from the liquid solvent, loosely speaking), or instabilities due to heat flow in the solvent. Whatever way those holes appear, the nanoparticles much prefer to stay wet and so are carried on the “tide” of the solvent as it dewets from the surface…


(The figure above is taken from a review article written by Andrew Stannard, now at King’s College London. Before his move to London, Andy was a PhD researcher and then research fellow in the Nottingham Nanoscience Group. His PhD thesis focused on the wonderfully rich array of patterns that form as a result of self-assembly in nanostructured and molecular systems. Fittingly, given the scale-independent nature of some of these patterns, Andy’s research career started in astronomy (with the aforementioned Peter Coles.))

As those holes expand, particles aggregate at their edges and ultimately collide, producing a Voronoi tesselation when the solvent has entirely evaporated. What’s particularly neat is that there are many ways for the solvent to dewet, including a fascinating effect called the Benard-Marangoni instability. The physics underpinning this instability has many parallels with the Rayleigh-Taylor instability that helped produce Lynda Jackson’s wonderful painting.

But how do we program our physical computer? [3] To input the positions of the points for which we want compute the tesselation, we need to pattern the substrate so that we can control where (and when) the dewetting process initiates. And, fortunately, with (suitably treated) silicon surfaces, it’s possible to locally oxidise a nanoscale region using an atomic force microscope and draw effectively arbitrary patterns. Matt Blunt, now a lecturer at University College London, got this patterning process down to a very fine art while he was a PhD researcher in the group over a decade ago. The illustration below, taken from Matt’s thesis, explains the patterning process:


Corporate Identity Guidelines™ of course dictate that, when any new lithographic or patterning technique becomes available, the very first pattern drawn is the university logo (as shown on the left below; the linewidth is approximately 100 nm.) The image on the right shows how a 4 micron x 4 micron square of AFM-patterned oxide affects the dewetting of the solvent and dramatically changes the pattern formed by the nanoparticles; for one thing, the characteristic length scale of the pattern on the square is much greater than that in the surrounding region. By patterning the surface in a slightly more precise manner we could, in principle, choose the sites where the solvent dewets and exploit that dewetting to calculate the Voronoi tesselation for effectively an arbitrary set of points in a 2D plane.


There’s a very important class of unconventional computing known as wetware. (Indeed, a massively parallel wetware system is running inside your head as you read these words.) The lateral computing strategy outlined above might perhaps be best described as dewetware.

I very much hope that Sean and I can explore other forms of lateral/unconventional computing in future Computerphile videos. There are a number of influential physicists who have suggested that the fundamental quantity in the universe is not matter, nor energy — it’s information. Patterns, be they compressed and encrypted binary representations of scientific data or striking and affecting pieces of art, embed information on a wide variety of different levels.

And if there’s one thing that connects artists and scientists, it’s our love of patterns…

[1] And that’s just for starters. YouTube has been dragged, kicking and screaming every inch of the way, into a belated and grudging acceptance that it’s been hosting and fostering some truly odious and vile ‘content’.

[2] On a tangential point, it frustrates me immensely that public engagement is now no longer enough by itself. When it comes to securing funding for engaging with the public (who fund our research), we’re increasingly made feel that it’s more important to collect and analyse questionnaire responses than to actually connect with the audience in the first place.

[3] I’ll come clean — the nanoparticle Voronoi tesselation “calculation” shown above is just a tad artificial in that the points were selected “after the event”. The tesselation wasn’t directed/programmed in this case; the holes that opened up in the solvent-nanoparticle film due to dewetting weren’t pre-selected. However, the concept remains valid — the dewetting centres can in principle be “dialled in” by patterning the surface.

The Silent Poetry of Paint Drying

The painting has a life of its own. I just let it come through.

Jackson Pollock (1912 – 1956)

Over the last six weeks or so, I’ve had the immense pleasure of collaborating with local artist Lynda Jackson on a project for Creative Reactions — the arts-science offshoot of Pint of Science   I don’t quite know why I didn’t sign up for Creative Reactions long before now but after reading Mark Fromhold‘s wonderful blog post about last year’s event, I jumped at the chance to get involved with CR2019. The collaboration with Lynda culminated in us being interviewed together for yesterday’s Creative Reactions closing night, which was a heck of a lot of fun. The event, compered by PhD student researcher Paul Brett (Microbiology, University of Nottingham), was expertly live-tweeted by another UoN researcher (this time from the School of Chemistry), Lizzie Killalea

I’ve been fascinated by the physics (and metaphysics) of foam for a very long time, and was delighted that the collaboration with Lynda serendipitously ended up being focused on foam-like painting and patterns. When we met for the first time, Lynda told me that she had a burgeoning interest in what’s known as acrylic pouring, as described in this video…

…and here’s a great example of one of Lynda’s paintings, produced using a somewhat similar technique to that described in the video:


I love that painting, not only for its aesthetic value, but for its direct, and scientifically beautiful, connection to the foam patterns — or, to give them their slightly more technical name, cellular networks — that are prevalent right across nature, from the sub-microscopic to the (quite literally) astronomically large (via, as I discuss in the Sixty Symbols video below, the Giant’s Causeway and some stonkingly stoned spiders)…

Our research group spent a great deal of time (nearly a decade — see this paper for a review of some of that work) analysing the cellular networks that form when a droplet of a suspension of nanoparticles in a solvent is placed on a surface and subsequently left to its own devices (or alternatively spin-dried). Here’s a particularly striking example of the foams-within-foams-within-foams motif that is formed via the drying of a nanoparticle-laden droplet of toluene on silicon…


What you see in that atomic force microscope image above — which is approximately 0.02 of a millimetre, i.e. 20 micrometres, across — are not the individual 2 nanometre nanoparticles themselves, but the much larger (micron-scale) pattern that is formed during the drying of the droplet; the evaporation and dewetting of the solvent corrals the particles together into the patterns you see. It’s somewhat like what happens in the formation of a coffee stain: the particles are carried on the tide of the solvent (water for the coffee example; toluene in the case of the nanoparticles).

Lynda’s painting above is about 50 cm wide. That means that the scale of the foam created by acrylic pouring is ~ 25,000 times bigger than that of the nanoparticle pattern. Physicists get very excited when they see the same class of pattern cropping up in very different systems and/or on very different length scales — it often means that there’s an overarching mathematical framework; a very similar form of differential equation, for example, may well be underpinning the observations. And, indeed, there are similar physical processes at play in both the acrylic pouring and the nanoparticle systems: mixed phases separate under the influence of solvent flow. Here’s another striking example from Lynda’s work:


Phase separation and phase transitions are not only an exceptionally rich source of fascinating physics (and, indeed, chemistry and biology) but they almost invariably give rise to sets of intriguing and intricate patterns that have captivated both scientists and artists for centuries. In the not-too-distant future I’ll blog about Alan Turing’s remarkable insights into the pattern-forming processes that produce the spots, spirals, and stripes of animal hides (like those shown in the tweet below); his reaction-diffusion model is an exceptionally elegant example of truly original scientific thinking. I always hesitate to use the word “genius” — because science is so very much more complicated and collaborative than the tired cliche of the lone scientist “kicking against the odds” — but in Turing’s case the accolade is more than well-deserved.

I nicked the title of this post — well, almost nicked — from a quote generally attributed to Plutarch: “Painting is silent poetry, and poetry is painting that speaks.” It’s very encouraging indeed that Creative Reactions followed hot on the heels of the Science Rhymes event organised by my UoN colleague Gerardo Adesso a couple of weeks ago (see Brigitte Nerlich‘s great review for the Making Science Public blog). Could we at last be breaking down the barriers between those two cultures that CP Snow famously identified so many years ago?

At the very least, I get the feeling that there’s a great deal more going on than just a superficial painting over the cracks…