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February 2013 Archives

Of physics and famine

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The Harvesters

Pieter Bruegel the Elder’s painting The Harvesters (1565) shows a scene of plenty, but
people like the peasants depicted in it would have been all too familiar with famine.
(Courtesy: The Metropolitan Museum of Art)

By Margaret Harris

Physics and medieval history don’t overlap that often. I should know: I got an undergraduate minor in medieval and renaissance studies in part because I wanted a break from doing physics. So the fact that this arXiv paper and this documentary have both come out in the past 10 days is about as unusual as – well, finding a medieval king buried in a car park.

Fascinating as the discovery of Richard III’s skeleton is, though, I’m going to write instead about the arXiv paper, which proposes something even more remarkable: a possible link between space weather and episodes of famine in late medieval Europe.

The paper focuses on the years 1590–1702, a period during which Europe’s population suffered repeatedly from famine. Over the same period, the Sun was experiencing a decades-long lull in activity, known as the Maunder minimum. Might there be a connection?

To answer this question, the paper’s authors – physicist Lev Pustilnik and economist Gregory Yom Din – begin by summarizing the evidence for a connection between space weather and local weather. Overall, this appears fairly convincing, if a bit circumstantial. For example, a 1997 study found a link between cosmic rays and cloud cover, while a 2004 paper demonstrated a similar correlation between global atmospheric circulation and level of activity in the Earth’s magnetosphere.

With the principle of a connection thus established, Pustilnik and Yom Din go on to suggest three conditions under which space weather could lead to famine:

• Local weather has to be in a “threshold state” such that it is sensitive to space weather. For example, if there is no water vapour present, clouds won’t form even if space weather is “seeding” the Earth’s atmosphere with lots of extra ions.

• Harvests must be sensitive to weather anomalies. This is more likely in areas of so-called “risk farming”, where conditions are marginal enough that a few days of bad weather can completely wipe out a crop.

• The area has to be economically isolated, such that local shortages cannot be ameliorated by buying grain from elsewhere.

To test these hypotheses, Pustilnik and Yom Din begin by comparing levels of solar activity with grain prices in 17th century England. Between 1590 and 1700, the price of grain in England and the abundance of 10Be isotopes (a proxy for solar activity) in Greenland ice cores exhibit an almost exactly inverse relationship. High prices correspond to periods of low solar activity and vice versa. Several other European markets that the authors studied also showed strong correlations between grain prices and solar activity, but in southern Europe, where crops are more likely to suffer from drought than from excess rain, prices tended to spike during solar maxima rather than minima.

Things get a bit shakier when the authors turn their attention to 19th century Iceland. In this case, famines seem to correlate with both minima and maxima in solar activity. Pustilnik and Yom Din claim this is what they expected to see, but don’t really say why; in particular, they don’t explain why the Icelandic pattern should differ so markedly from the English one.

Still, it’s an interesting study, and reading it stirred up some memories from my brief foray into medieval studies. In particular, I thought of a book called Lost Worlds whose author, a Swiss historian called Arthur Imhof, makes unusually good use of hard data in analysing what life was like for an ordinary person in early modern Europe. Might his book have something to add to the famine/space weather debate?

I skimmed my copy of Lost Worlds a couple of times before I located the bit where Imhof writes about famine. Tree-ring data and written sources from the 16th and 17th centuries, he notes, indicate a long series of harsh winters and summers with too much rain, resulting in exceptionally bad growing conditions. As a result, he adds, “our ancestors had more reason to beg for their daily bread between 1550 and 1700” than they did at almost any point before or since.

This is, of course, almost exactly the same period that Pustilnik and Yom Din studied, and it’s nice to see that Imhof’s sources corroborate their grain-price data. But Imhof wasn’t interested in climate for climate’s sake. Instead, he was trying to demonstrate that populations in areas prone to famine, plague and war became traumatized by their repeated misfortunes. You’d have to read the book to appreciate Imhof’s argument in full, but among other things, he suggests that people in these “unlucky” areas developed fatalistic attitudes to life, death and birth. These attitudes show up not only in religious beliefs, but also in data on infant and maternal mortality. For example, even in peaceful, plague-free years, more than one-third of babies born in the plague-prone and war-torn German village of Gabelbach died in infancy. In “luckier” villages, the comparable figure was one in eight.

Where does this leave us regarding space weather? Well, if we add Imhof’s conclusions to Pustilnik and Yom Din’s, it seems that the behaviour of heavenly bodies could have influenced not only the viability of medieval grain crops, but also the habits and attitudes of the people who tended them – perhaps even to the extent of determining whether their children were likely to live or die. That might not be very surprising to the peasants of 17th century Gabelbach, who lived in a more religious age (and, according to Imhof, believed fervently in astrology). But to me, it’s absolutely mind-blowing – and a whole lot more interesting than England’s “Tricky Dick” turning up in a car park.

Condensing matters drastically at Imperial College

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Martin Archer

Martin Archer (centre) tackles the fundamentals of quantum mechanics.

By James Dacey

Will the universe go on expanding forever? Why should we care about climate change? Can we make objects invisible?

These are Big questions with a capital B, which individually could occupy the mind of a scientist for an entire academic career. In fact I am sure they have.

But yesterday at Imperial College in London we asked a bunch of physicists to tackle questions of this size and stature and to answer them in 100 seconds or less – using nothing more than a white board and a few marker pens. It was a seriously tough challenge in the overlapping arts of brevity and clear communication.

The presentations were filmed as part of our 100 Second Science video series and they will be joining the existing batch of these “mini lectures”. The picture above shows the PhD student and radio DJ Martin Archer preparing for his moment in the spotlight during which he tackled several questions on the fundamentals of quantum mechanics.

One of the questions Martin addressed related to one of the seemingly paradoxical implications of quantum mechanics: “Is Schrödinger’s cat dead or alive?”. I won’t spoil Martin’s 100 Second Science video on this famous thought experiment, but let us know your thoughts on this question by visiting our Facebook page and taking part in our poll where we ask:

Is Schrödinger’s cat dead or alive?

It must be one or the other at any given time
It exists in a superposition of dead and alive
It could be dead and alive in separate universes
Another outcome is possible

We look forward to your responses. Look out for more in this series of films over the coming months.

By Hamish Johnston

Bubbles are wonderful things – as well as giving children hours of fun, they provide physicists with a number of fascinating phenomena to study and genuine mysteries to solve.

One curious effect that physicists have known about for some time is that tiny air bubbles in water will last much longer when they are stuck on a surface – rather than floating freely. A free bubble with a diameter of 100 nm or less will only survive a few microseconds, while a bubble of similar size on a surface can endure for days.

Why is this interesting, you might wonder? For one thing, controlling nanobubbles can be very important when designing tiny machines that shift fluids about. A coating of nanobubbles could make it easier for a fluid to flow along a tiny channel. Conversely, bubbles in the wrong place could gum up the works. Nanobubbles could someday be designed to carry drugs to specific places in the body, popping on arrival.

Such applications could be one step closer thanks to work published today in Physical Review Letters. Joost Weijs and Detlef Lohse at the MESA+ Institute for Nanotechnology at the University of Twente in the Netherlands have devised a theoretical model that tries to explain why bubbles on a surface stick around for so much longer.

The pair say that two important effects are at play. The first – and most obvious – is that bubbles stuck to a surface aren’t spherical, but rather are flattened out on the surface. This means that they have radii of curvature that are much larger than spheres of similar volume. It’s well known that the smaller the radius of curvature, the faster that gas leaks from a bubble.

The second reason is related to the fact that the nanobubbles are fixed on a surface and tend to be surrounded by other nanobubbles. This means that the liquid in the vicinity of the surface becomes saturated with escaping gas molecules that must diffuse away. This puts the brakes on gas that is trying to diffuse out of the bubbles. Free bubbles don’t have this problem because as they rise in a liquid, they move away from gas molecules that they have released.

You can read the paper here.

This isn’t the first time that a paper has appeared in Physical Review Letters about nanobubbles. In 2011 Lohse and two other colleagues at Twente published this novel proposal about how nanobubbles on surfaces could be recycling gas molecules.

By Matin Durrani


It’s the first of the month so – as if by clockwork – the February issue of Physics World is now ready for your enjoyment, in print, online and through our apps.

Our lead news story this month is about how Barack Obama, who was sworn in for a second term as US president last month, deals with the US “fiscal cliff” and what impact any resolution has on funding for science.

Elsewhere, we examine the lasting impact of two famous astronomers – Fred Hoyle and Sir Bernard Lovell. The former’s impact is felt most acutely in the “Hoyle state” – a short-lived excited form of carbon-12 that holds the clue to life in the universe but is still baffling today’s best nuclear physicists. As for Lovell, his notorious visits to the Soviet Union in the 1960s at the height of the Cold War might have been frowned upon by authorities in the West, but they set the tone for international collaboration and helped to pave the way to today’s ITER fusion experiment.

There’s also a great feature on how researchers are gaining valuable information about the black hole Cygnus X-1. Plus don’t miss Peter Kenny’s lateral thoughts about the mysteries of mathematical subtraction and find out why friends hold the key to career success.

If you’re a member of the Institute of Physics, you can access the entire new issue online through the digital version of the magazine by following this link or by downloading the Physics World app onto your iPhone or iPad or Android device, available from the App Store and Google Play, respectively.

If you’re not yet a member, you can join the Institute as an IOPimember for just £15, €20 or $25 a year via this link. Being an IOPimember gives you a full year’s access to Physics World both online and through the apps.

For the record, here’s a rundown of highlights of the issue:

Fiscal cliff leaves funding concerns – Impending cuts to science may temper the optimism that some physicists had over the re-election of Barack Obama, as Peter Gwynne reports

The rocky road to reform – A power struggle at one of Serbia’s largest and best known science institutes has led to its director being forced to resign after allegedly failing to restructure the lab, as Mićo Tatalović reports

Thinking big about the future – As the US eyes a manned mission to an asteroid or Mars, Kirstin Matthews and Padraig Moloney argue that NASA needs better support for basic research – especially nanotechnology – to realize such ambitions

Game-show physicsRobert P Crease explains why science is never an idealized process that operates following simple rules

The secret of life – Life as we know it would not be possible were it not for a particular nuclear energy level of carbon-12 predicted 60 years ago by Fred Hoyle. But the true nature of this energy level remains one of the biggest unsolved questions in nuclear physics, say David Jenkins and Oliver Kirsebom

A fusion of minds – Mystery still surrounds the visit of the astronomer Sir Bernard Lovell to the Soviet Union in 1963. But his collaboration – and that of other British scientists – eased geopolitical tensions at the height of the Cold War and paved the way for today’s global ITER fusion project, as Richard Corfield explains

The swan’s dark heart – Astronomers discovered what they thought was the first black hole more than 40 years ago but have only recently verified its identity by establishing its distance, mass and spin. These fascinating observations are yielding new insights into Cygnus X-1’s past and future, as Ken Croswell explains

Another side of black holesKulvinder Singh Chadha reviews Gravity’s Engines: the Other Side of Black Holes by Caleb Scharf

Visible improvementsJames Davenport reviews Visual Strategies: a Practical Guide for Scientists and Engineers by Felice Frenkel and Angela DePace

Forget about networkingMarc Kuchner argues that if scientists really want to advance their careers, they should concentrate on making friends instead of networking

Borrowing from nowhere – In this month’s Lateral Thoughts, Peter Kenny gets all mixed up with subtraction