My Boston friends sometimes wonder aloud, “What do you people do for amusement out there in the Berkshires in the winter?” After all, it’s not like we’ve got cool bars to frequent, venues for live music or any museums to go to. And we’re so far from Boston that no one even blows up random items left on the sidewalk to keep us entertained. (It’s okay - you couldn’t find them in the snow anyway.)

The answer is pretty simple. We build stuff. Odd stuff. Dysfunctional hot tubs. Mongolian-inspired round houses (gers). Trebuchets. That sort of thing.

The most recent project is the result of a multiple-year conversation between me and one of my favorite conspirators, Daniel Beck. Daniel, his lovely wife and a mutual friend participated in Burning Man a few years back and came back with wonderful photos and great stories. I griped that an event that would require me to take two weeks off from work and rent an RV to bring whatever art we’d built probably wasn’t going to happen. Why didn’t someone start an East Coast alternative for those of us several days away from the playa?

And so we started developing a web joke - Freezing Man, the east coast alternative to Burning Man, held in late February in scenic Savoy Mountain State Forest (an especially cold and snowy corner of rural northwestern MA, which happens to be in Daniel’s back yard.) We’d put up photos of oddly dressed, semi-nude, glowstick-waving revellers standing waist deep in snow and wait to see who showed up for the gathering next February. (Yes, I realize there’s a Burning Man regular who hands out icecream as Freezing Man. And that BoingBoing has posted photos of the playa in the snow today. It’s a coincidence, I promise.)

But first, we needed a Man. The goal was a Burning-Man-like figure shivering in the cold, covered with icicles. We’re partway there, I think. Willy (as I’ve been thinking of him) is living in my back yard, attempting to grow a good coat of ice. Unfortunately, our first attempts to ice him (spraying him with cold water in near-zero weather) didn’t yield the icing we’d like - I’m now patiently waiting for the freezing rain we’re promised on Friday.

Daniel’s got a nice set of photos of the Man posted on his blog, currently dominating his front page. I’m particularly fond of this shot, where Daniel’s trying to anchor our statue firmly in the snow. We built Freezing Man by measuring Daniel and trying to build body parts roughly twice his size. Clearly we’re not very good at math.

Put a 15 foot tall wooden man in your backyard and you’ve got to expect some reaction from your neighbors. But our county houses some notable eccentrics - a neighbor on Green River Road in Williamstown has a 20-foot tall blue chair in his back yard for no discernable reason. Chesire, MA, has as its primary tourist attraction a giant concrete cheese press, a monument to the massive wheel of cheese the town presented to Thomas Jefferson in 1802.

A shopping plaza a few miles south used to feature a massive ship sinking into the parking lot - it was dismantled in 2002, removing one of the more picturesque attractions of that corner of Pittsfield, MA. (The piece was by Dustin Shuler, who’s done some truly amazing things with cars.)

In other words, I don’t really expect anyone to notice. That is, unless masses of glowstick-wielding revellers show up for our festival and start camping out in the ger. After all, we don’t have much tolerance for weirdness out here.

Bill of Jewels in the Jungle is running a fascinating set of articles for Black History Month, focusing on the Afrodeutsche (Afro-German) identity. Bill is an African American who’s lived in Germany for many years - he’s a leading Afrophile blogger, always an interesting source for news and perspective on African issues and one of the most welcome commenters on this blog. Bill is spending the month exploring the history of Black people in Germany with the help of friends who are German historians.

One of the stories Bill and friends have told is the remarkable tale of Dr. Anton Wilhelm Amo, an Akan man who was the first known sub-Saharan Africa man to attend a European university. Dr. Amo became a noted lecturer and empiricst philosopher, teaching at the University of Halle and the University of Jenna. A recent post, subtitled “Amo’s Ghost”, asks an amazing range of questions about the little-known academic:

7. What really caused Amo to give up his professorship at the University of Jena in 1746-47? Was it that he lost his sponsorship from Anton Ulrich due to the duke’s death or was it due to the rising tide of xenophobia, racism, and abuse amongst his fellows and students?…

8. Was Amo the only African black living in Germany in the 1700’s or were there other Africans in royal households who lived a similar lifestyle? Where are the African women and children in this 18th Century German story? …

There are unanswered questions about the Afrodeutsche in the more recent past, including the fate of Afrodeutsche during the Shoah - historians estimate that 10-25,000 Afrodeutsche died at the hands of the Nazis. As a survivor, Hans-Jürgen Massaquoi, noted, “As the only kid with brown skin I had no place to hide. The Jews had a Star of David on their clothes but my very appearance singled me out.” Doing some very cursory searches at the US Holocaust Museum, I’m having a hard time finding any information - or even acknowledgement - of the persecution of the Afrodeutsch. One description of the museum’s collections mentions that subject areas include, “Nazi persecution of Roma and Sinti (Gypsies), homosexuals, Jehovah’s Witnesses, political dissidents, Poles, and Soviet prisoners of war.”

(It looks like a good start for anyone researching this topic would be a 1997 documentary, “Hitler’s Forgotten Victims“, which documents the fate of Afrodeutsch during the war, but also traces German use of sterilization and concentration camps to German South-West Africa, now Namibia.)

Black History Month has become a staple of American school curiculums, to the point where it’s the subject of satire on everyone’s favorite television show, Jon Stewart’s The Daily Show. Senior Black Historian Larry Wilmore suggests we stop celebrating the event, noting: “White people have to pretend to care about Black people. Black people have to pretend to care about history. It’s a lose-lose.”

But the sorts of research Bill and his colleagues are doing isn’t treading familiar ground - it’s bringing forward stories most of us haven’t heard. I’ve got high hopes that Bill and his friends will continue their exploration long beyond the end of this month.

There’s been a good deal of discussion in the online security community over the last 48 hours about vulnerabilities and attacks on the Tor anonymization service. This discussion is in reaction to a paper published by the University of Colorado about a theoretical attack on the Tor network, which got amplified on Slashdot on Sunday afternoon. I woke up yesterday to a mailbox full of questions about whether I still recommended Tor as a tool for anonymous blogging and backchannel chat from security researchers over “blogstorm” resulting from the paper.

Which means that, by the time I actually read the paper - Tuesday morning - I feel like I’m way behind the curve. Maybe that’s the price I pay for actually reading the paper… :-)

The paper, “Low-Resource Routing Attacks Against Anonymous Systems”, by Kevin Bauer, Damon McCoy, Dirk Grunwald, Tadayoshi Kohno and Douglas Sicker is not a report documenting an attack that’s taken place on the Tor network. It’s what’s called an “attack paper” - an outline of a possible vulnerability in the tool designed to help the authors of Tor prevent real-world attacks. This isn’t the first attack paper designed to find possible weaknesses in Tor - there are several known attacks that could compromise the anonymity of Tor, but most require substantial computing resources.

The “new” attack - which builds on a known attack - is intriguing because it could possibly be mounted with a much smaller set of technical resources. Again, no one is contending that such an attack has been mounted, and Tor’s creators - in their response to the blogstorm - offer reassurances that it would be pretty obvious to them if such an attack occurred.

Here’s how the attack works:

Tor provides anonymity by creating a chain of routers between you and the website you’re accessing. You contact a router (the entry node), it contacts a second router (a mix node) and that router contacts a final router (the exit node) which contacts the website. Anyone monitoring your computer sees you access that entry node but can’t follow your connection (because of encryption) through to the exit node or the website you’re accessing. Anyone monitoring the website you access can trace you back to the exit node, but no further.

A known problem with Tor is that it’s possible to know what computers are accessing what sites if you’ve got control of both the entry and the exit node of a connection. If the computer at 71.123.23.85 sends out a POST request at at 12:34:50 (as seen at the entry node) and ethanzuckerman.com sees a comment posted at 12:34:51 (as seen from the exit node), you can make a guess that 71.123.23.85 posted the comment. Correlate requests over a period of time and you can make some good guesses about what sites a user is accessing.

This known attack hasn’t been considered a major problem because it would be so difficult for an attacker to implement - you’d need to establish a lot of rogue Tor servers and register them with the Tor directory server to have a statistically significant chance of having control of both the entry and exit node. What’s novel in this new paper is that the authors have found a way of raising the chances of having control of both the entry and exit nodes.

They exploit the fact that networks like Tor want to route traffic through high-bandwidth nodes rather than bandwidth-constrained nodes. (This makes sense - if you’re surfing the net through Tor, you want to be sharing a big university data pipe, not sharing someone’s home cable modem.) If our attacker creates rogue Tor nodes that claim that they’ve got lots of bandwidth, the network is more likely to route traffic through those nodes.

In a laboratory setting, the paper authors introduced 6 rogue nodes to a network of 60 legitimate Tor nodes. In that lab setting, in a network where one in eleven nodes was compromised and advertising themselves as high bandwidth nodes, the researchers were able to establish what client was contacting what server in 46% of cases. Obviously, that’s a striking result - what’s more striking is the idea that an attacker might achieve this with a bunch of computers connected by cable modems, pretending to be high-bandwidth Tor nodes. This raises the spectre of virus-infected zombie computers running rogue Tor nodes and reporting back to a central server the information that you’re using Tor to surf NakedLlamas.com.

The good news is that this isn’t happening. To quote from the Tor developers’ blog:

We are aware of these kinds of potential attacks — but such a bandwidth overstatement attack, to be successful, would leave fingerprints all over the Tor directories. We have never seen such an attack “in the wild,” and we think it no more likely that this paper would make such an attack easier or more likely than it was a few years ago when another version of it was documented.

I’m not sure I agree with the last statement - it seems like a useful research breakthrough to point out that a node that misrepresents bandwidth requirements makes it possible to apply this attack more efficiently. But, reading between the lines, it sounds like Tor’s maintainers are a) controlling how many new Tor nodes are added to the directory servers and b) monitoring which servers are used most heavily, which would mean they’d have a very good chance of detecting such an attack were it taking place and heading it off.

It’s important to note that the authors of the paper have released a FAQ which states quite clearly that they don’t think their attack is a reason to stop using Tor:

ABSOLUTELY NOT! Despite our findings, Tor is the most secure and usable privacy enhancing system available. We believe that the system is safe for end-users; however, the system is experimental and the developers make no guarantees about the degree of privacy that it can provide. Let us re-iterate: Concerned users should NOT stop using Tor.

So let me reiterate that further:

- Tor is not perfect, but papers like this help make the system stronger. A paper like this allows the designers to make modifications to the system (likely to the bandwidth prioritization mechanism) to make the system stronger.

- No anonymizing system is perfect. Tor has been very good about making reasonable claims for their tools, something that not all anonymizing tools do.

- The strategies I outlined in my document on anonymous blogging with Wordpress and Tor still give a high level of certainty to bloggers that they can write online while disguising their identity. This isn’t a guarantee of perfect security, but I feel comfortable recommending the strategy to my friends in repressive nations.

There’s more to say about how people make decisions about security risks and about how to discuss security risks openly without generating panic, but that’s beyond the scope of this blog post. Hope to have time to write something about that later this week.

• Erik Emery Hanberg: The Politics of the Cactus
  Lovely post on Conservopedia, a wikipedia that attempts to relieve the “left-wing bias” of Wikipedia
  (tags: funny wikipedia uspolitics)
• Out of Africa - Reuters Blogs
  David Schlesinger’s post about Reuters’ new Africa project, which helps contextualize the GV relationship
  (tags: globalvoices africa blogs media journalism)
• Forests lure moose to Massachusetts | csmonitor.com
  We’ve got moose in Mass., which is evidently a bit of a mystery. (Haven’t seen a moose yet. Beavers, though, and black bear, and we hear coyotes all the time…)
  (tags: local berkshire)
• Ghana: Former U.N. Secretary-General Urged to Run for President - Worldpress.org
  Will Kofi Annan run for the Ghanaian presidency? Or is he too global a figure to take his place in local politics?
  (tags: ghana africa)
• Nazret.com EthioBlog - Ethiopia - U.S. silence worries Ethiopians
  Did Ethiopian cooperation with the US in Somalia give Zenawi a free pass from US pressure on human rights issues, repression of journalists, violence against protesters?
  (tags: africa ethiopia somalia uspolitics)
• How to boost trade within Africa : Lower barriers and diversify production
  Excellent article on the difficulties of trade between neighboring African countries and the importance of increasing regional trade
  (tags: africa trade globalization)
• SecondLLA - Second Life Liberation Army?
  A “military campaign” to fight for rights within Second Life, which evidently include ownership of Linden Labs. “The SLLA will not seek to harm the normal operation of the world and will only attack agents of the state and other strategically important si
  (tags: secondlife)

My friends at Kubatana posted an interesting set of documents today, the police announcements prohibiting demonstrations and rallies in several neighborhoods of Harare. The documents are works of bureacratic genius, reaching amazing lengths in their attempts to justify constraining the right of Zimbabwean citizens to protest the atrocious conditions they’re living in.

My personal favorite is the order banning demonstrations in the Chitungwiza district, a residential area about 15km south of the capital. Yes, the reasons given for prohibiting demonstrations in this community include the fact that windows were broken in the houses of two members of the opposition party. That, plus the fact that demonstrations are happening in other parts of Harare give the superintendant of police sufficient reason to ban rallies and demonstrations for a month.

Of course, the order has nothing to do with the fact that the people in Chitungwiza overwhelmingly support the opposition Movement for Democratic Change. Or that people in the community are finding it impossible to work in Harare because they can’t afford the commute into the city center, leading them to lose their jobs (which barely pay enough to buy bread.)

Image from Kubatana.net
Windowpanes were also broken in Harare Central when organizations including Women of Zimbabwe Arise went on “a rampage”. My friends at Kubatana helpfully post some terrifying photos of the rampaging Zimbabwean housewives and mothers. Be careful - you can put someone’s eyes out with those roses they’re carrying (The march was supposed to be on Valentine’s Day, but was moved a day earlier in the hopes that it would experience less police repression.)

What amazes me about Zimbabwe is the care the government takes to make sure that deeply illegal actions comply with the letter of the law. In some ways, it’s a refreshing change from abusive leaders who simply do what they want, like Guinea’s President Conte, who simply went to the local jail and released two friends who’d been imprisoned for fraud. But the result is a set of remarkable documents designed to keep an increasingly angry population from taking to the streets while remaining within the letter of the law, drafted with a touch that would have made George Orwell proud.

• Reuters/Second Life ? Second Life Sketches: Please stop doing that to the cat
  Warren Ellis: “Anyone who says that sexual activity is a tiny part of the SL experience is either stupid or knowingly lying.”
  (tags: secondlife humor funny)

• U.S. Used Base in Ethiopia to Hunt Al Qaeda in Africa - New York Times
  US Troops used a base in Ethiopia and made incursions into Somalia. Will the US media ever start talking about our involvement in Somalia?
  (tags: somalia ethiopia africa uspolitics)
• Market approach recasts often-hungry Ethiopia as potential bread basket | csmonitor.com
  Economist Eleni Gabre- Madhin believes that Ethiopia could be a grain exporter if market information gaps were corrected. Sounds like a job for TradeNet. But infrastructure, roads, access to ports is also going to be a huge obstacle.
  (tags: africa ethiopia economics trade globalization ghana)
• TeleRead: Bring the E-Books Home
  Excellent blog on e-books, user-generated content, open content
  (tags: blogs books publishing olpc)
• Signs mount of end game for Zimbabwe’s Robert Mugabe - International Herald Tribune
  Dark, ugly overview of the situation in Zimbabwe, with prediction that Mugabe can’t hold power much longer
  (tags: zimbabwe africa)
• A Tale of Two Todays ? Media SITREP
  Interesting insight from jbracken - are we so reluctant to criticize our politicians in the US, because we don’t have a monarchy to fawn over, as in the UK? What would it take for the US press to aggresively question US leaders?
  (tags: uspolitics UK journalism media)

Sometimes my hunger for new data sets gets the best of me. After staring at Adrian White’s map of global happiness, I just had to graph some data, run some regressions and try to offer some speculation on why some regions seem happier than others.

In other words, ignore everything I’ve written here. It’s an interesting train of thought, but not one that can be statistically verified at this point. I may try to graph just the data nef collected from various surveys, which leaves a smaller set of countries to play with, but I’m not going to be able to do that until my real job leaves me alone for a few days. Grrr…

The founding fathers of the United States declared independence from Great Britain with the memorable phrase “life, liberty and the pursuit of happiness“. The phrase was inserted by Thomas Jefferson as a departure from Adam Smith’s more capitalistic formulation, “life, liberty and the pursuit of property.” (The frequent blurring of property and happiness in American poplar consciousness may well trace itself back to this tension…)

In recent years, some governments - notably the government of Bhutan - have suggested that a measure of gross national happiness might be a better evaluation of national priorities than a purely economic measure like “gross domestic product per capita”. And academic journals have appeared, dedicated to happiness studies, or the more academic-sounding “Subjective Well-Being”. These journals produce lists of happiest and unhappiest nations, which are always good for a quick media story, proclaiming Denmark the happiest place on earth and Burundi the most miserable.

Adrian White from the University of Leicester has compiled a map of global happiness, using responses to the Satisfaction With Life Scale questionaire, a simple document designed to measure subjective well-being. It’s so simple that I can include it in its entirety:

Respond to these statements with a number from 1-7, where 1 represents strongly disagree and 7 represents strongly agree:

- In most ways my life is close to my ideal.
- The conditions of my life are excellent.
- I am satisfied with my life.
- So far I have gotten the important things I want in life.
- If I could live my life over, I would change almost nothing.

If you ask those questions of people in 180 nations and normalize the data so that your unhappiest country (Burundi) equals 100 and your happiest (Denmark) equals 273 and color code all countries by their happiness (darker equals happier), you get this lovely map.

A quick glance at the map tells you that Africa’s an unhappy place and that North Americans, Western Europeans and Aussies are happy folks. My first guess was that the distribution of happiness correlated closely with wealth. White asserts that the strongest correlation is to health, followed by wealth and access to education.

I played a bit with the subjective well-being data and graphed most of the data points from White’s work against life expectancy and saw a pretty some correlation (R2 = 0.3779, which is close to the R=0.7 White asserts…) What interested me was the fact that the countries seemed to cluster into three distinct areas: countries that were happy and healthy, countries that weren’t very healthy or happy, and a group of depressive nations that were healthy but unhappy.

Click on image to enlarge

(If I were a statistician, I’d do something clever like run an ANOVA test to demonstrate variance between the groups and some way to segment the set. But I’m a geek with too much time on my hands, so I just drew some circles and lines. If you’re a statistician and want to play with this data, lemme know…)

Eliminate that top cluster and you could get a pretty good equation to model the data from the black line and the lower red line. Eliminate the bottom cluster and you could use the top red line and black line. In other words, it looks a little like there’s two separate groups of nations here, one which has a strong relationship between health and happiness, another where that relationship is much less clear.

Click on image to enlarge
Most interesting to me are the nations that are outliers of the curve - nations that appear to be unusually happy or unusually unhappy as based on their life expectancy. Nations in the upper right corner of the graph are ones we’d expect to be happy, as their citizens have long lives (Denmark, Switzerland). In the lower left of the graph, we’ve got nations we’d expect to be unhappy because life is short (Zimbabwe, Burundi).

The other corners are the interesting ones. The upper left corner are nations that are unhappy despite long lifespans. You’ll note some common characteristics to these nations: they’re members of the former Soviet Union. (They’re also very cold, but other chilly nations like Canada, Iceland, and Scandinavia are quite happy…) Despite a long lifespan, Armenia is one of the unhappiest nations on earth (something I can confirm from my visits to the country.)

It’s harder to characterize the lower right corner, where nations are happier than we would expect. Bhutan lives in this corner, which we might expect from the country that invented gross national happiness. And nations that are both very happy and unusually happy include a number of tropical paradises, suggesting that if you, personally, would like to be happy, moving to the Bahamas might not be a bad start.

But moving further down the happiness scale, we see a number of nations that are happier than we’d expect based on their lifespans. Many of these nations are in sub-Saharan Africa, and a number of them (Ghana, Kenya, South Africa, Mali, Botswana, Namibia) are nations that people often point to when pointing towards the hope for African growth and development. Others include nations where civil war has settled into relative peace and prosperity (Sierra Leone, Guinea-Bissau, Mozambique.)

You could offer an interesting narrative based on this - the idea that nations are happiest when citizens think things are getting better, saddest in nations where things seem to be getting worse. Not all former Soviet nations are depressed, but those that are include some nations that fared well under the old regime and are struggling in a new economy. And the happy African nations are the ones where things are changing from very bad to not so bad, or have the potential to become leaders on the continent. As Laurie Anderson asked in her beautiful “Same Time Tomorrow”, “Are things getting better? Or are they getting worse?”

Unfortunately, there’s another way to explain the African results - life isn’t too bad in Namibia, for instance, except for one of the highest HIV prevalence rates in the world. (The same could be said for Botswana, Zambia and several other countries in this cluster.) HIV brings down the life expectancy creating a cluster of countries where life isn’t as hard as it is in Burundi, but it is tragically short. Find a way of meaningfully addressing HIV and these countries might join the family of happy, healthy nations instead of being a statistical anomaly and humanitarian disaster.

Is a post on happiness allowed to end on this sort of unhappy note? This one does.

A few years ago, as Alex Steffen (founder of Worldchanging.com, where I serve as chairman of the board of directors) and I were getting to know each other, we both attended the Pop!Tech conference in Camden, Maine. One of the speakers had circulated yellow and green plastic cards to the audience, and asked us to vote on various propositions by holding up one card or another. The questions were meant to be divisive and ethically difficult. One asked whether we thought it was justifiable to introduce Nile Perch into Lake Victoria, likely unbalancing the ecosystem, but providing much-needed protein for local fishermen. I put up a yellow card to indicate that I thought it was justifiable and caught Alex looking at me, green card in his hand. We raised eyebrows at one another and went on to the next question.

There are a lot of situations where environmentalists and sustainable development advocates see eye to eye. We can both get psyched about small-scale solar and wind power, about farming techniques that use less chemical fertilizer, about Dr. Amy Smith’s amazing research on charcoal alternatives.

And then there are issues where we’re just not going to see eye to eye, like the hundred mile diet. James MacKinnon and Alisa Smith decided to spend a year eating only food grown within a hundred miles of their Vancouver, BC home as a way of calling attention to the environmental costs of the typical North American diet. The diet - and the related concept of “food miles” - has become very trendy within the environmental movement. A quick glance on Worldchanging turned up several articles, including an eat local contest, an Iowa State University study on the economic impact of transporting food, and a meditation on local food and national security.

There’s lots of good reasons to seek out local food: it often tastes better, is fresher, forces you to meet your neighbors and gives you an insight into what foods do and don’t grow in your region. (I’m a proud member of our local organic farm, which is one of the pioneers in the CSA movement.) But measuring the environmental impact of a foodstuff based on how many miles it travelled is misleading at best. There’s impact from fertilizer, pesticides, packaging and machinery, as well as the energy expended in actually cooking the food, which can be a major component of the energy cost of a plate of food. A university study in New Zealand, which understandably wants to downplay the environmental impact of shipping lamb from the South Pacific to the UK, argues that farming in NZ is so efficient in comparison to the EU that producing agricultural goods in NZ and shipping them thousands of miles created fewer emissions than producing them in the EU.

NZ’s ag minister, Jim Anderton, makes the argument that “food miles” aren’t really about environmentalism:

“The concept of food miles is both flawed and too often promoted by those motivated by self-serving objectives rather than genuine environmental concerns,” Jim Anderton said. “It is being used in Europe by self interested parties trying to justify protectionism in another guise.”

Which brings me to the article that got me thinking about food miles today, a story by Victoria Averill for the BBC. Averill talks to Kenyan farmers who’ve made the change from growing food for local export to food for global export. 65% of the agricultural produce grown in Kenya is designated for export, half of it to supermarkets in the UK. Economic advisors have been pushing rural farmers to plant “high value” crops for decades - growing flowers for export puts much more money in a farmer’s pocket than growing maize to sell to his neighbors. And Kenya’s pursued this course very aggresively, to the point where horticulture is the second largest industry in the country after tourism.

So the announcement by British supermarket chain Tesco that they’re going to start putting a “carbon count” on their packaging is making Kenyan farmers very nervous. Kenyan food - which is widely sold in Tesco - will now be designated with an airplane on its packaging. And since Tesco is committed to reducing the percent of food that’s flow in from 2-3% to 1%, Kenyan farmers won’t be able to sell as much produce to UK stores.

A Kenyan farmer who Averill interviews points out that his personal carbon footprint as an agricultural producer is a lot lighter than that of his UK consumers:

He points to the simple gravitational water irrigation system that flows through his smallholding, admitting he has never been in a plane, rarely travels by bus and uses nothing but his hands to grow, fertilise and harvest his top quality green beans, which then appear on a supermarket shelf in Europe.

Situations like this leave African farmers feeling helpless and cheated. Kenyan farmers followed well-meaning international advice, and many have benefitted from increased revenue from growing high value crops. But if that international market dries up, they’re producing crops that there’s no local market for - a move like this could leave tens of thousands of farmers without a livelihood, at least until they can retool their crop mix.

Certainly it’s admirable that Tesco wants to limit its environmental impact. Lots of the changes they’re proposing for lighting and heating their stores and for making their distribution system more efficient are excellent ones. But limiting agriculture from Africa isn’t likely to have a major environmental impact - one study suggests that a complete boycott on air-freight produce from Africa would reduce UK emissions less than 0.1%. And it’s certainly going to raise questions about whether a move like the one Tesco is proposing is about environmentalism, protectionism, or simple ill-considered hype.

It’s very easy to cover a flat surface with a regular pattern of geometric shapes - in mathematics, this set of problems is referred to as “tiling”. It’s much harder to cover a surface with a pattern that doesn’t repeat. In 1961, mathematician Hao Wang tried to prove that any set of tiles that cover a plane do so periodically - i.e., with a regular pattern. A number of mathematicians proved him wrong, first with a set of 20,000 tiles, then 104, then 92.

The big breakthrough in tiling came in 1973, when British mathematician Roger Penrose demonstrated sets of six, four and two tiles that could cover a surface non-periodically. His tiles have spawned a great deal of interest and research, and help an interesting problem in physics: quasicrystals, which are materials which difract light like crystals, but aren’t regular, periodic shapes like most crystals. Instead, they share much of the symmetry that Penrose’s tiles display.

While Penrose’s breakthrough is a fascinating chapter in mathematics, it turns out that he may be over 500 years late in solving the problem of non-periodic tiling. According to Peter J. Lu of Harvard University and Paul Steinhardt of Princeton University, the artists who decorated the Darb-i-Imam shrine in Isfahan, Iran, in 1453 used a non-periodic pattern that’s virtually identical to Penrose’s tiles.

The patterns, called girih, are composed from a small regularly shaped tiles, tesselated into complex patterns. The researchers believe that the technique was developed in the 13th century and by the 15th century had developed to a level of sophistication where non-repeating patterns were possible.

Peter Lu was inspired to pursue this research topic based on a pattern he’d seen on a building in Uzbekistan. I can think of no better argument for researchers to get out of the lab and onto airplanes more often.