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February 2012 Archives

When the Earth changes face

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By James Dacey

When an earthquake strikes, it can change a landscape dramatically within just a few seconds. Tectonic plates that usually creep past each other suddenly speed up to several thousand kilometres per hour, which can result in large displacements of the land.

An international team of scientists has managed to build the most detailed before-and-after picture to date of a landscape altered by an earthquake – a region near Mexicali in northern Mexico that was struck by a magnitude-7.2 quake in April 2010.

The geoscientists, working with the National Center for Airborne Laser Mapping, used LiDAR to survey the region, which had already been mapped by the Mexican government in 2006 using the same technique. This colourful animation shows the extent to which some areas of land were thrust upwards while other areas were forced down during the 2010 earthquake.

LiDAR – an abbreviation of “light detection and ranging” – involves flying over a region and firing a laser beam at the ground then detecting the reflected beams. By measuring the time delay between the transmission of the pulse and the detection of the reflected signal, scientists can estimate the elevation of the land surface.

In the study, researchers used LiDAR to measure surface features to within a few inches over an area of 360 square kilometres, within a few days. Publishing their findings in the journal Science, the scientists have identified features such as warping of the ground surface adjacent to faults, which did not show up in earlier ground surveys. These features, they say, could help geophysicists to better understand how earthquakes occur within multiple-fault systems like the one in northern Mexico.

“The 2010 Mexicali earthquake did not occur on a major fault, like the San Andreas, but ran through a series of smaller faults in the Earth’s crust. These minor faults are common around major faults but are under-appreciated,” says Michael Oskin of the University of California, lead author of the Science paper.

For an insightful introduction to earthquake science and the efforts to predict the occurrence of earthquakes, you can watch this short film just released on Keep an eye on this website throughout March for further content relating to the physics of the Earth.

Crowd outside the session on Majorana fermions

An over-capacity crowd greeted Leo Kouwenhoven’s talk on Majorana fermions

By Margaret Harris

The hottest talk of the APS March Meeting so far took place yesterday, when Leo Kouwenhoven revealed that his group at TU Delft in the Netherlands may have observed Majorana fermions in one-dimensional nanowires.

Majorana fermions have a curious property – they are their own antiparticles – and particle physicists have been looking for fundamental Majorana fermions for decades. A few years ago, condensed-matter physicists got in on the act too, seeking evidence of Majorana-like behaviour in fermionic quasiparticles such as those formed by electrons in superconductors. But so far, no-one has ever found conclusive evidence that such particles exist – so if this nanowire result holds up, it would be quite the coup for Kouwenhoven and his group.

Unfortunately, Kouwenhoven’s talk was so popular that the crowd overflowed into the hallway outside, and with conference centre staff talking anxiously about fire regulations, it proved impossible for me to squeeze in (Eugenie Reich of Nature was luckier – you can read her summary here). So instead, I headed to the room next door, where Krastan Blagoev of the US National Science Foundation was delivering an inspiring talk on the kinetics of metastatic cancer.

Map of obesity rates in the US in 2004 and 2008

Obesity rates in the US in 2004 and 2008. (Courtesy: Lazaros Gallos)

By Margaret Harris at the APS March Meeting

The data on obesity are pretty unequivocal: we’re fat, and we’re getting fatter. Explanations for this trend, however, vary widely, with the blame alternately pinned on individual behaviour, genetics and the environment. In other words, it’s a race between “we eat too much”, “we’re born that way” and “it’s society’s fault”.

Now, research by Lazaros Gallos has come down strongly in favour of the third option. Gallos and his colleagues at City College of New York treated the obesity rates in some 3000 US counties as “particles” in a physical system, and calculated the correlation between pairs of “particles” as a function of the distance between them. This calculation allowed them to find out whether the obesity rate among, say, citizens of downtown Boston was correlated in any way to the rates in suburban Boston and more distant communities.

It wouldn’t have been particularly surprising if Gallos’ team had found such correlations on a small scale. The economies of Boston and its suburbs are tightly coupled, for one thing, and their demographics are also not so terribly different. But the data indicated that the size of the “obesity cities” – geographic regions with correlated obesity rates – was huge, up to 1000 km. In other words, the obesity rate of downtown Boston was strongly correlated not only with the rates in the city’s suburban hinterland, but also with rates in far-off New York City and hamlets in northern Maine.

This correlation was independent of the obesity rate itself – there are “thin cities” as well as obese ones – and also far stronger than correlations in other factors, such as the economy or population distribution, would suggest. The exception, intriguingly enough, was the food industry, which also showed tight correlations between geographically distant counties.

Gallos isn’t claiming that the food industry is causing obesity. He also doesn’t discount the importance of food choices and genetic factors: what you eat and who you are will clearly play a big role in determining whether or not you, as an individual, will become obese. However, he points out that our genes haven’t changed that much since the US obesity epidemic began in the 1980s, and neither, presumably, has our willpower. The difference, he says, is that on a societal level, increasingly large numbers of us are living in an “obese-o-genic” environment, and “the consensus is that the system makes you eat more”.

Gallos says he’ll post this research on arXiv sometime in the next few days [UPDATE 29/2/12: here’s the link to the paper]. In the meantime, I’ll be testing his hypothesis personally in the obese-o-genic environment of a major scientific conference, complete with multiple breakfasts, receptions and lunches. Pass the pastries, please!

Photo of Boston Common sign

Boston Common and the Park Street Church, part of the city’s “Freedom Trail”.

By Margaret Harris at the APS March Meeting in Boston

The American Physical Society’s March Meeting doesn’t really kick off until tomorrow morning, but with many of the 6000+ delegates arriving a day early, we’re rapidly heading towards a critical mass of physicists here in Boston. Even the good citizens of New England’s largest city are starting to notice the influx; as I was walking along the “Freedom Trail” of historic landmarks earlier today, I met a park ranger who estimated that I was 10th physicist he’d spoken to that afternoon.

Anyway, from tomorrow until Thursday I’ll be swapping sight-seeing trips for talks on a wide range of physics topics. Many of the sessions are devoted to superconductivity, which remains a popular field a quarter of a century after the famous “Woodstock of Physics” March Meeting when the first high-temperature superconductors took centre stage.

Physicists with a keen interest in graphene will face some particularly tough decisions on which talks to attend, with 39 separate sessions devoted to carbon’s newest and sexiest (well, unless you prefer diamonds or buckyballs) allotrope.

There’s also some intriguing-sounding interdisciplinary sessions on the physics of cancer and the aftermath of the Fukushima nuclear incident. And finally, I’m hoping to learn more about the latest nifty experiments in my PhD field of atomic and molecular physics.

First, though, I need to go eat some of Boston’s famous seafood…

By James Dacey

The big physics story of the week has been the news that neutrinos may not travel faster than the speed of light after all. Researchers in the OPERA collaboration, in Italy, have identified an optical fibre in their experiment that may not have been functioning correctly at the time when the measurements were made.

hands smll.jpg

After all the excitement and speculation, could this “once in a century” result be caused by nothing more than a dodgy cable? Usually when a result like this vanishes into the ether, nobody is to blame except the media for blowing the story completely out of proportion in the first place. But in this instance, it has to be said that CERN and the OPERA collaboration did hold a special press conference last September to allow their researchers to present the findings to the world’s media.

If the faulty cable does explain the result, then I fear there could be a backlash against physics and the physics community. At best it will cause minor embarrassment and gentle derision of “easily excitable” physicists. At worst, it could lead to accusations of time-wasting, and ultimately it could weaken the reputation of physics as a serious science based on critical thinking and careful experimentation.

We want to know your opinion in this week’s poll.

Have physicists overhyped the superluminal-neutrino results?


Have your say by casting your vote on our Facebook page. As always, please feel free to explain your response by posting a comment.

There are, of course, several things to note. First is the fact that nothing has yet been proven, and the optical fibre may yet be innocent. What’s more, the OPERA researchers have always maintained that they are the result’s biggest critics. They vowed to continue to scrutinize all aspects of the experiment in search of systematic errors. So perhaps we should not be too surprised if the result does prove to be void because of something as seemingly trivial as a faulty cable.

It must also be said that the OPERA result was not the first time that a neutrino experiment had glimpsed possible superluminal speeds. In 2007 the MINOS experiment in the US recorded 473 neutrinos that appeared to have travelled from Fermilab near Chicago to a detector in northern Minnesota at speeds in excess of the speed of light. MINOS physicists reported speeds similar to that seen by OPERA, but their experimental uncertainties were much larger.

The final point to note is that the media (and, yes, that includes this website) have clearly got just as excited as the researchers. If physicists created the story, we’ve certainly made a song and dance about it and kept it in the news ever since.

Whatever you think, let us know on Facebook.

In last week’s poll, we addressed another area of physics that has been surrounded by a lot of hype in recent years – quantum computing. We asked you whether you thought that quantum computing is theoretically possible. Some 70% of respondents believe that it is, while just 4% think not. The remaining 26% chose the option of “being caught in a superposition of yes and no”.

Thank you for all of your votes and comments, and we look forward to hearing from you again in this week’s poll.

By Margaret Harris

I went to the University of Surrey last week for a science careers evening, and as I was chatting to some students afterwards, one of them asked a fascinating question. “We’re always hearing that the UK needs more graduates in STEM fields,” she said, using the ever-present acronym for science, technology, engineering and mathematics. “But if that’s true, why are so many of us struggling to find jobs?”

I’ve been asking myself the same question for some time. As Physics World’s careers editor, I receive many upbeat press releases touting the importance of STEM disciplines in building the knowledge economy, pulling the country out of recession and so on. But I have also watched, with impotent sympathy, as some of my scientifically trained friends search in vain for jobs. So what is wrong with this picture?


By Tushna Commissariat

I know that many Physics World readers want to be up to speed when it comes to the delicate matter of redefining the kilogram using Planck’s constant (h). You will therefore be pleased to learn that a paper published today in the journal Metrologia has a detailed description of using a device known as a “watt balance” to achieve an accurate value for h with the required level of certainty in the near future.

The international definition of the kilogram is currently based on a lump of platinum–iridium housed by our metrologist friends at the International Bureau of Weights and Measures (BIPM) in Paris. These guys aim to provide the basis for a single, coherent system of measurements throughout the world, traceable to the International System of Units (SI). But, unfortunately, periodic inspections of the lump – known as the International Prototype of the Kilogram (image on the right, courtesy BIPM) shows that it has been losing some of its mass slowly over time, because of chemical interactions between its surface and the air, making it rather unstable and, hence, not the ideal marker for a standard.

The SI is the most widely used system of measurement for commerce and science, and comprises of seven base units: metre, kilogram, second, kelvin, ampere, mole and candela. To ensure that all these values remain stable over time and can be universally reproducible, they should ideally be based on fundamental constants of nature. The kilogram, however, is the only unit still defined by a physical artefact.

What a watt balance can do is to provide a way of redefining the kilogram in terms of Planck’s constant, which relates the frequency of a photon to its energy. First proposed by Brian Kibble at the UK’s National Physical Laboratory (NPL) in 1975, the watt balance relates electrical power to mechanical power. By applying two quantum-mechanical effects – the Josephson effect and the quantum Hall effect – electrical power can be measured in terms of h.

Last October, delegates to the General Conference on Weights and Measures (CGPM) agreed that the kilogram should be redefined in terms of h; but they stipulated that a final decision would only be made when there is sufficient consistent and accurate data to agree on an accepted value for h.

The Metrologia paper describes what needs to be done to achieve the required level of precision above five parts in 108. It provides a measured value of h and extensive analysis of possible uncertainties that can arise during experimentation. Although these results alone are not enough, consistent results from other measurement institutes using the techniques and technology described in this paper will provide an even more accurate consensus value and a change to the way the world measures mass – possibly as soon as 2014.

In the paper, author Ian Robinson from NPL details the work that the lab carried out from 2007 to 2009, including the many in-depth alterations that Robinson made to the device itself as well as trying to weed out uncertainties and achieve the most accurate value. While NPL’s watt balance is currently being used at the National Research Council in Canada, Robinson is sure that it will give considerably greater accuracy and will provide an accurate h within the next two years.

Currently the lowest uncertainty for an h value – at 36 parts in 109 – has been achieved by scientists at the National Institute for Standards and Technology(NIST) in the US, who have their own watt balance. The BIPM has asked for at least one experiment to achieve an uncertainty of 2 parts in 108, while the other experiments must have an agreement of a value with an uncertainty of 5 parts in 108 before it will allow the kilogram to be defined by h.

When I spoke to Robinson, he said that the NPL watt balance, now in its new home in Canada, is primed to take the most accurate readings. “Over the past six years or so, I have made innumerable changes to the apparatus; each part has been custom-built by Kibble and I, and all of this is explained in detail in the paper. All over the world, people are working very hard to find out where the discrepancies occur,” he says. This means that a consensus should be reached soon.

To find out more about the changes to the apparatus, the series of measurements using different weights and the unexpected uncertainty that cropped up in Robinson’s experiment just as he was poise to achieve the same uncertainty level as the NIST value and the cause for the discrepancy, take a look at Robinson’s paper at this link.

To learn more about redefining the kilogram, take a look at this Physics World blog, feature and video.

A waiting game

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By Michael Banks

Square Kilometre Array

Artist’s impression of the proposed Square Kilometre Array site in Austrialia (Courtesy: Swinburne Astronomy Productions)

I was rather hoping for more when I opened a press release from the Square Kilometre Array (SKA) organization this morning.

SKA, costing €1.5bn, is a proposed ground-based telescope that will allow researchers to probe the first 100 million years after the Big Bang for clues about galaxy evolution, dark matter and dark energy.

SKA will consist of around 2000–3000 linked antennas spread from a central 5 km “core” containing about 50% of the collecting area out to far-flung stations as much as 3000 km away. The telescope will then have the same collecting area as a hypothetical steerable dish 1 km across.

Two rival bids are going head to head to host the telescope: one led by Australia and the other by South Africa. The Australian design calls for a core in the west of the continent, with out-stations stretching eastwards to New Zealand. The South African project relies on a core in the Karoo region of the Northern Cape province, with the array extending northwards to eight neighbouring countries, including Madagascar and Kenya.

A decision on where to site SKA was widely expected to be made in February, and now the independent SKA site advisory committee has just submitted its evaluation report and site-selection recommendation to SKA’s board of directors.

Unfortunately for us mere mortals, we will not know the contents of the report until a later date. The press release gave no hint of who may host SKA, only saying that the seven members of SKA organization – which includes China, Italy and the UK – will now have a “face to face” meeting in “late March or early April” to consider the report’s conclusions and possibly make a decision about the location of the site.

If no consensus is reached at that meeting, then the members will “agree on the next steps in the process”. This one may drag on for some time to come.

By Hamish Johnston at the AAAS Annual Meeting, Vancouver, Canada

Depending on how you express it, Moore’s law has held up remarkably well over the past 40 years. In particular, chipmakers have been able to double the number of transistors that can be squeezed onto a chip every two years. This explains why the mobile phone in your pocket is more powerful than the most advanced “supercomputers” of the early 1970s.

Round about 2004 however, one aspect of this exponential growth hit the buffers – it became very difficult to remove the vast amount of heat produced by all these tightly packed circuits. The result being that it is not possible to use all circuits to their full potential. This problem has the ominous moniker of “dark silicon”.

Looking into the not-so-distant future, another problem is expected to crop up when the size of insulating structures in circuits drops below about 4 nm. At this point, electron tunnelling between circuits is expected to put an end to Moore’s law.

One way round this, according to Ralf Cavin of the Semiconductor Research Corporation, is to make the electrons heavier and therefore less likely to tunnel. While this might sound crazy, an electron in a solid has an effective mass that is often greater than its mass in free space. The thing that I don’t understand about this solution is that the speed at which a transistor operates is related to the effective mass of the electrons. The heavier the electron, the slower the speed; so it seems this is at odds with sustaining Moore’s law.

Ultimately, engineers will have to look beyond Moore’s law, and that was the topic of a session where Cavin spoke at the American Association for the Advancement of Science (AAAS) meeting here in Vancouver.

Cavin is keen on in carbo electronics – devices that are based on the remarkably efficient information processing done by living organisms. The benefits, according to Cavin, are many. For one thing, biological molecules such as DNA can store data at much higher densities than the ultimate upper limit of semiconductor devices. Living systems are also highly parallel and extremely energy efficient. On the downside, living circuits are much slower than silicon.

I’m not sure when your mobile phone will contain in carbo devices, if ever, but work has begun in that direction.

Tying qubits in knots

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Photo of a knot

By Hamish Johnston at the AAAS Annual Meeting, Vancouver, Canada

Some of the world’s leading experts on quantum computing are here in Vancouver for the American Association for the Advancement of Science (AAAS) annual meeting – and it’s been great to hear them speak and to also interview some of them.

One topic that has come up several times is the idea of topological quantum computing. A major challenge for those trying to build practical quantum computers is how to protect the “quantumness” of their fragile devices from the destructive effects of environmental noise and heat.

One approach is to take advantage of the topological nature of some quantum states. One example involves quasiparticles called anyons that are predicted to exist in 2D semiconductors. One feature of anyons is that they cannot overlap with each other as they travel through space and time. The result is that the anyons exist in quantum states called “braids” that criss-cross each other.

A key feature of the braids is that they are robust to noise and heat. Indeed, to destroy such a state it must be unravelled much like untying a knot – a process that takes time and effort. This is unlike a more conventional quantum state such as the spin of an electron, which can be destroyed by a simple nudge from a random magnetic field.

Michael Freedman of Microsoft Station Q in Santa Barbara is one of the pioneers in developing the theory of topological computing, and he spoke at the conference. He left the audience with this vision for the future: “There is a serious prospect that quantum computing will change the face of computation.”

Other speakers had a complementary take on this. Scott Aaronson of the Massachusetts Institute of Technology believes that quantum computing and the emergence of quantum computers will give physicists new insights into quantum physics. “Quantum computing has opened a two-way street between physics and the science of computation,” he said.

The essential guide to topological computing can, of course, be found in Physics World.

Ariel hardhat

Building ARIEL

By Hamish Johnston at the AAAS Annual Meeting, Vancouver, Canada

One of the pleasures of my job is that I get to talk to people who are passionate about physics. But nothing prepared me for Lia Merminga, who has to be the most enthusiastic physicist I have ever met. Merminga is head of the accelerator division at TRIUMF in Vancouver – which started as a particle-physics facility back in 1968 but has since branched out into nuclear, medical, biological and condensed-matter physics.

I was at the lab yesterday, dodging the puddles as we toured the campus under leaden skies. The highlight of the tour was getting a close-up look at the cyclotron, which was shut down for maintenance.

You can see the photos I took during the tour on our Flickr page.

I also spoke to Merminga about the Advanced Rare Isotope Laboratory (ARIEL) electron accelerator facility that is currently being built at TRIUMF. Indeed, I suspect much of her enthusiasm comes from the fact that she has what must be a dream job for an accelerator physicist – she’s in charge of building a brand-new accelerator!

I spoke with Merminga about many aspects of ARIEL, so look out for an interview sometime in the future on

Geordie Rose

By Hamish Johnston, reporting from Vancouver, Canada

Yesterday I took a cab out to nearby Burnaby to have a chat with Geordie Rose, a physicist who is co-founder of the quantum-computer maker D-Wave systems. That’s Geordie on the right standing next to one of the firm’s famous black boxes.

What’s inside the box? I had a look. The box itself is a shield that protects its contents from electromagnetic fields that would wreak havoc with D-Wave’s quantum bits (qubits) – which are superconducting flux qubits. In simple terms, each qubit is a little magnet that could easily be perturbed by stray fields.

Also in the box is a dilution refrigerator, which cools the chips to near absolute zero. D-Wave uses “dry” fridges that don’t need to be topped up with costly liquid helium. Indeed, Rose says that the firm has played an important role in the development of dry fridges.

The fridge cools an integrated circuit that contains hundreds of flux qubits. They are arranged in a 2D array where each is coupled with its nearest neighbour, creating an Ising model on a chip.

I also stopped by to chat to D-Wave’s Suzanne Gildert (below), who is developing the firm’s Developer Portal, where programmers can learn about how to write code for the systems. The portal is in a beta version at the moment but a full-blown portal will soon be available to all.

Suzanne Gildert

Coming away from D-Wave, you can’t help thinking that the company has cracked the challenge of creating a viable and scalable quantum computer. Indeed, you can even buy one, if you want. But Rose admits there are lots of challenges ahead before quantum computing goes mainstream – and he thinks the best way forward is to keep building and keep improving the systems.

You can see more photos from my visit on out Flickr page.

Quantum weirdness

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By Matin Durrani

Quantum physics is notoriously counter-intuitive and difficult to grasp, which is perhaps why the subject is often invoked to explain other seemingly counter-intuitive and difficult-to-grasp areas of life.

But that doesn’t mean that wheeling out the subject necessarily makes any sense.

So here’s to the former Bishop of Southwark, Thomas Frederick ‘Tom’ Butler, whose comments on the Thought for the Day slot on BBC Radio 4 this morning (at about 1.47) are a classic of the genre.

The bishop begins, for some reason, by talking about the search for the Higgs boson (or Higgs “bos’un” as he irritatingly puts it) at CERN’s Large Hadron Collider, which, he reveals to the world, “will shortly be reactivated”. (I presume he means restarted after the scheduled winter shut-down as the scientists on the machine have happily been taking data for more than two years now.)

Having brought up the LHC, Butler then jumps suddenly into quantum physics, bemoaning his lack of understanding of the subject. But that’s okay, we’re told, because Niels Bohr once said that “those who aren’t shocked when they first come across quantum theory can’t possibly have understood it”. (Quote a heavyweight from science – that’ll impress the listeners.)

And so to the heart of the matter: fundamental entities can be both particles and waves, which is, er, a bit like religion really. “Paradoxically it [quantum mechanics] has made some of the traditional problems of the nature of God easier to understand,” says the bishop, pointing out, for example, that Jesus is both human and divine.

Butler admits he found it hard, when he was younger, to come to terms with this paradox. “I found this both/and faith world difficult to grasp,” he says. “Surely this paradox couldn’t be right?”

Ah, but all’s well now, thanks to quantum physics. “It tells us the world is paradox. The fundamental nature of existence is both/and.”

But if you have any lingering doubts over the validity of quantum physics, don’t worry. “Hopefully we’ll soon have the Higgs boson to give the theory the stamp of approval.”

You can relive the whole item here – jump to about 1.47 minutes.

View from Vancouver

Snowy mountains and the sea

By Hamish Johnston at the AAAS Annual Meeting, Vancouver, Canada

I have just registered for the American Association for the Advancement of Science (AAAS) meeting in Vancouver. Above is what you see from the convention centre – nice view!

More from Vancouver later, I’m off to D-Wave to talk about quantum computers.

By Hamish Johnston

As I mentioned yesterday, I’m on my way to Vancouver for the annual meeting of the American Association for the Advancement of Science (AAAS), where the future of quantum computers is on the agenda.

I’m looking forward to catching up with Scott Aaronson of the Massachusetts Institute of Technology, who has been in the news lately because of his $100,000 challenge. The mathematical physicist is offering this princely sum to anyone who can convince him that scalable quantum computers are impossible. This might seem like easy money – after all, physicists have struggled for years to build even the most primitive quantum processors, and scaling these up to make a working quantum computer seems a tall order.

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But Aaronson isn’t talking about hardware, instead he wants you to disprove the underlying quantum physics that would make a quantum computer tick. “This is a bet on the validity of quantum mechanics as it’s currently understood,” he told me recently. Can he raise the money? Yes, and he even thinks it would be well spent because disproving some or all of quantum mechanics would lead to a revolution in physics. Has he received any serious entries so far? No, but there is no time limit on the challenge so get your ideas to Aaronson.

In this week’s Facebook poll we are asking if you think Aaronson will hang on to his hard-earned cash?

Do you think that quantum computing is theoretically possible?

Yes, for sure
No way
I’m caught in a superposition of yes and no

Last week we asked who is the most inspiring of the current communicators out of a list of six famous physicists.

The winner with 34% of the vote is Brian Greene of Columbia University. Runner-up is Oldham’s own Brian Cox, with 18%. And you don’t have to be called Brian to be on the podium because third place goes to Michio Kaku of the City University of New York with slightly less that 18%.

It’s interesting to note that Greene, Cox and Kaku have all had their own TV shows recently, so that could explain their popularity.

Rounding off the results, in fourth, fifth and sixth places, respectively, are Stephen Hawking, Neil deGrasse Tyson and Lisa Randall.

Other suggestions from readers included Neil Turok, who is director of the Perimeter Institute in Canada, and Jim Al-Khalili of the University of Surrey – who famously declared that he would eat his underpants if neutrinos can travel faster than the speed of light. Other suggestions were Lee Smolin and Lawrence Krauss. If you would like to hear Krauss in action, he will be giving a live lecture on on 6 March.

Take part in our photo challenge

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Photograph through sunglasses

By James Dacey

Physics is without doubt an incredibly visual subject. From the distant stars and galaxies observed by telescopes to the technicolour bursts captured by particle detectors, images play an inspirational role in our understanding of the physical universe at all scales.

At the heart of scientific imagery is light. Indeed, in recognition of the vital role light plays in science and engineering, a proposal has been made for an International Year of Light in 2015 to promote improved public and political understanding of the central role of light in the modern world.

We want to celebrate the connections between light and the physical world by asking you to share your photos. Take part in the Physics World photo challenge by submitting photos to our Flickr group on the theme of “Light In Physics”. Please add your photos by Wednesday 29 February and then after this date we will choose a selection of our favourite images to be showcased on

Nature is teeming with photo opportunities. It might be the dramatic light shows produced by aurora, pearl-like water droplets glistening in a spider’s web, or the shimmering structural colours paraded by animals such as peacocks and butterflies. Or you may choose to capture an image indoors, maybe a laboratory demonstration of a basic optics principle or perhaps a fascinating array of laser light. Be as creative as like.

Please also feel free to write a caption to share the story behind the image. Your photos may be an interesting physical phenomenon, or may have required some inventive and time-consuming photography. Expensive equipment is not necessarily required, however. People prove every day that you can capture an inspiring snapshot using the most basic of cameras, even the one on your mobile phone.

We look forward to your photos – happy snapping!

By Hamish Johnston

Tomorrow I will be winging my way to Vancouver to attend the annual meeting of the American Association for the Advancement of Science – the AAAS. I have lots on for the next few days, including a trip to the TRIUMF accelerator lab to find out how physicists there are planning to make medical isotopes using an accelerator rather than having to rely on ageing nuclear reactors.

Geordie Rose

I will also be spending a lot of time talking to people about quantum computing (QC). Indeed, a good chunk of the programme at the AAAS is devoted to QC, a field in which Canadian physicists have excelled.

One such physicist is Geordie Rose (right), founder of the quantum-computer maker D-Wave Systems, which is based in Vancouver. I plan to visit D-Wave on Friday, when I hope to find out what is in that giant box that often appears behind Geordie.

What I’m not looking forward to is the 10-hour flight – if only quantum teleportation worked for macroscopic objects.

Wake up, little SUSY

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By Hamish Johnston

I should have known better than to listen to rumours. But some of the most reliable gossips in the particle-physics blogosphere had being saying to expect news of evidence for a supersymmetry particle – or sparticle – to come from the Large Hadron Collider today.

Ximo Poveda

So, earlier today I donned my headphones and pointed my browser at a talk given by Ximo Poveda of the ATLAS experiment (right), who was tipped to be the bringer of good news. He went through four or five searches for several supersymmetric partners of various quarks and leptons – squarks and sleptons called the stop, stau and sbottom – and each time the conclusion was “we see nothing beyond the Standard Model”.

Supersymmetry (or SUSY) is an attractive route beyond the Standard Model because it offers a solution to the “hierarchy problem” of particle physics, provides a way of unifying the strong and electroweak forces, and even contains a dark-matter particle. Many physicists hope the LHC will confirm SUSY’s central prediction – that for each of the Standard Model particles there exists a heavier sparticle sibling. But so far, nothing beyond the Standard Model has emerged.

Oh, well. On a brighter note, CERN has announced that in 2012 it will be running the LHC at the higher collision energy of 8 TeV, instead of the 7 TeV collisions that took place in 2011. As well as boosting the chances that sparticles will be spotted, the move to a higher energy should also make it clearer whether the Higgs boson has been found with a mass of about 125 GeV – as suggested late last year.

The downside is that higher-energy collisions require greater current flowing through the LHC’s superconducting magnets – and there is a problem with the electrical connectors between magnets. In 2008 the LHC failed spectacularly when one of these connectors overheated; let’s hope that doesn’t happen again.

Physics of the fringe

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Hair data

The shape of a real ponytail at various lengths is given by “a”. Calculated shapes by “b” and “c”, where “c” includes a term for frizziness. (Courtesy: American Physical Society)

By Hamish Johnston

Here is some research that is truly on the fringe – or a “big bangs theory” for our readers in North America.

Physicists in the UK have published a paper in Physical Review Letters entitled “Shape of a ponytail and the statistical physics of hair fiber bundles”.

Written by Raymond Goldstein of the University of Cambridge, Robin Ball of the University of Warwick and Patrick Warren of the shampoo-maker Unilever, the article offers an “equation of state for the human ponytail”. Amazingly, the physicists are not the first to calculate an equation of state for hair – that was done back in 1946 by C F van Wyk, who was interested in the compressibility of wool.

According to the UK-based trio, the shape of a ponytail is defined by the competing effects of the elasticity of individual hairs, gravity and mutual interactions between hairs in a bundle. And because a ponytail can contain as many as 100,000 hairs, the problem is best addressed using statistical physics.

The researchers derived a relatively simple equation of state that includes the “Rapunzel number”, which they describe as a dimensionless measure of ponytail length. The team then used the equation to predict the shape of a ponytail as a function of length and compared the results with the shapes of ponytails made with real human hair.

The derivation that best describes a real ponytail also includes a term that reflects the observation that hair becomes “frizzier” as it grows out.

What’s next for the trio? The researchers want to apply their newfound equation of state to study the dynamics of ponytails – how they swish back and forth when the wearer is running.

You can read the paper here, but a subscription may be needed.

Pondering the power law

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Hamish Johnston

It’s a long-running joke in the newsroom that physicists see power laws everywhere. Indeed, a quick scan of the arXiv preprint server reveals physics papers that apply power-law analysis to a wide range of topics from cosmology to geography.

But how many of these studies actually produce useful results? Not many, argue two applied mathematicians in the UK.

A power-law description of nature says that a physical quantity or probability distribution is proportional to an exponential power of another quantity. A simple example is the inverse-square law that describes the gravitational attraction between two masses. A more statistical formulation is the Gutenberg–Richter law, which describes the number of earthquakes experienced in a location as a function of earthquake magnitude.

But what does power-law analysis actually tell us about the physical properties of a system? Its proponents argue that if different things – say earthquake frequency and measles outbreaks – share the same power law, then there must be something similar about the fundamental dynamics that drives both systems. This train of thought has already proved very useful in the study of thermodynamic phase transitions, for example, where seemingly unrelated systems change phase in exactly the same manner.

But should physicists expect the same success when power laws are applied to other systems? Writing in today’s issue of Science, Michael Stumpf of Imperial College London and Mason Porter of the University of Oxford argue that, so far, the track record is not very promising.

They argue that many power-law studies have poor statistical underpinnings and don’t shed much light on the underlying mechanisms of the systems of interest. Indeed, they write that “even the most statistically successful calculations of power laws offer little more than anecdotal value”. That is fighting talk, so expect a robust response from the power-law community in the letters pages of Science.

Hmm, I wonder if the time gaps between letters will follow a power law? You can read all about that particular effect in this Physics World article by Albert-László Barabási, who is one of the discipline’s leading exponents.

You can read Stumpf and Porter’s article here, but it may require a subscription.

By James Dacey

Some have dubbed it the “Brian Cox effect”, others cite a whole raft of reasons, but all concerned agree that physics in the UK has undergone something of a popularity transformation in recent years.

Indeed, applications to study undergraduate physics (including astronomy) increased by 34% between 2004 and 2009, rising year on year. And the trend appears to be continuing unabated.

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According to the nuclear physicist Jim Al-Khalili of the University of Surrey – himself something of a media darling these days – there have been 320 applicants for 60 physics places this year at his institution alone, a 40% increase from last year. And this increase has occurred despite a 10% overall decline in applications at the university – blamed on the nationwide rises in tuition fees introduced this year.

To me, it is impossible to attribute the recent resurgence in physics to one specific reason. But I believe it is clear that the likes of Brian Cox and Jim Al-Khalili have helped to rebrand physics, thanks to their passionate communication of science in the popular media and their knack for explaining difficult ideas using simple, everyday concepts.

In this week’s Facebook poll question, please give us your opinion on the following.

Who is the most inspiring of the current physics communicators?

Brian Cox
Brian Greene
Michio Kaku
Lisa Randall
Neil deGrasse Tyson
Stephen Hawking

And, of course, feel free to explain your choice or suggest an alternative communicator by posting a comment on the poll.

In last week’s poll we asked you a question related to particle physics. We wanted to know where you think the International Linear Collider (ILC) – a proposed successor to the Large Hadron Collider (LHC) – should be built.

Some 52% of respondents opted for CERN, the home of the LHC on the Franco-Swiss border. 30% went for Fermilab in the US, which hosted the LHC’s former rival accelerator, the Tevatron, which shut down towards the end of last year. 11% believe it is time for Japan to have its turn, following recent speculation in the Japanese press that the ILC could be built on the island of Kyushu. The remaining 6% believe that the ILC should never be built.

Thank you everyone for your responses and we look forward to your responses in this week’s poll.

Photograph of efflorescence

Efflorescence on a masonry wall (Courtesy: Mattes)

By Hamish Johnston

One thing you can say about most houses in the UK is that they are solid. All walls, including internal ones, tend to be made from masonry – bricks in Victorian and Edwardian homes, and cement blocks in more modern buildings. It’s rare to see the flimsy-looking wooden frames that miraculously become houses in North America, for example.

But there is a downside to this solid construction. Masonry – and older bricks in particular – tend to suck-up moisture from the ground. Indeed, this is such a common problem in the UK that they named a sitcom after it – Rising Damp.

One symptom of rising damp is efflorescence, which means “flowering out”. This refers to crystals of salts that grow out from the surface of masonry as the damp evaporates into the air. Efflorescence can be a real pain on interior walls because it can stain paintwork and push-off wallpaper. I should know, because we used to have it in the dining room!

Efflorescence has also fascinated physicists because, rather than emerging as a uniform coating of salt, the crystals tend to appear in clumps – but exactly why was a mystery.

But now, Marc Prat and colleagues at the University of Toulouse, France, have done experiments and computer simulations that suggest that several factors are involved in determining the locations of salt flowers.

One is that the rate of evaporation is often not uniform across a wall. Not surprisingly, moisture is drawn to regions of the surface where air currents or other factors boost evaporation, and this causes more efflorescence in these areas. The irony, of course, is that reducing humidity and increasing ventilation could actually encourage efflorescence!

Turning their attention to the network of tiny pores that exist in masonry, the team worked out that certain pathways are extremely efficient at transporting water to the surface, while others are not. The researchers concluded that the salt flowers form where these efficient pathways emerge at the surface. Once a crystal is established on the surface, its presence increases the flow of water through that particular pathway, further depriving surrounding less-efficient pathways of liquid. The result is regions with large crystals, and other regions with no salt.

Finally, they tried to explain why the salt crystals grow outwards from the surface, rather than spreading out. The reason, it seems, is that the moisture would rather travel through a salt crystal than along a masonry surface. Putting all of this together, the team believes that it has made a good first effort at understanding efflorescence.

The research is described in Phys. Rev. Lett. 108 054502 and you can read the paper here.

The sights and sounds of Fermilab

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Wilson Hall at sunset

By Margaret Harris

Last autumn I visited Fermilab to learn more about the US particle-physics lab’s plans for the future now that its flagship particle accelerator, the Tevatron, has closed for good.

You can read more about those plans in this article, but if you’d like a slightly more visual guide to how the lab is changing, I’ve put some photographs from my trip on Physics World’s Flickr page.

I’m hardly a professional photographer, but it’s easy to take good photos in a place as beautiful as Fermilab, with its spacious Midwestern skies, iconic structures, and famous herd of American bison. But even if pretty pictures aren’t your thing, the photos also illustrate some of the changes going on at the lab, with the empty, slightly forlorn-looking CDF control room contrasting sharply with the buzz of activity in Fermilab’s neutrino-research areas.

In other Fermilab news, the Chicago-based composer Mason Bates apparently found the lab’s soundscape as inspiring as its landscape. Bates is the composer-in-residence at the Chicago Symphony Orchestra, and last year he visited Fermilab to record material for a new composition called Alternative Energy. According to the website for the symphony, the piece blends ambient noises from the lab with percussion and orchestra, and it had its première on Thursday 2 February. You can watch a video of Bates making his recordings here.


By Tushna Commissariat

This year the European Southern Observatory (ESO) is celebrating its 50th birthday. In honour, ESO plans to release a monthly “then and now” comparison image that shows how much things have changed over the past half of a century at ESO’s two main observatory sites (La Silla and Paranal), at ESO offices in Santiago de Chile and at its headquarters in Garching, Germany.

February’s photos of choice (images above courtesy of ESO/J Dommaget) depict the La Silla Observatory in the late 1960s and the present day. Only one telescope is visible in the historical image – the ESO 1 m Schmidt telescope, which saw first light in 1971. The present-day image has two new telescopes visible – the MPG/ESO 2.2 m telescope (left) and the New Technology Telescope on the peak to the right. According to ESO, the MPG/ESO 2.2 m telescope has been in operation since 1984 and its construction is apparently the reason why the modern-day photograph could not be taken from exactly the same spot as the one from the 1960s. It also points out that back in the day, astronomers would sleep in the huts running along the right-hand side of the road. Luckily, researchers now have the luxury of using a more comfortable hotel on the edge of the site.

It is also interesting to note the cars in both images. ESO informs me that the car in the historical image is a Volkswagen 1600 Variant, while now all ESO vehicles on site at La Silla – such as the Suzuki 4WD in the new image – are white, to improve visibility at night.

Keep an eye out for more “then and now” images from ESO in the months to come.

Closing the gender gap

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By Matin Durrani
My eye was caught this morning by a new report from the Institute of Physics, which publishes, about the number of physicists at UK universities.

Entitled Academic Physics Staff in UK Higher Education Institutions, you can read the full report here, but what I found particularly interesting were the data on women in physics.

The report reveals that the proportion of staff in UK physics departments who are women has risen steadily from 13% in 2003/04 to 16% in 2009/10. (See figure above: data in it are from the UK’s Higher Education Statistics Agency.)

As one might expect, the biggest rises are at more junior levels, with the proportion of female lecturers going up from 11.3% to 19.8% over that period. Senior-lecturer numbers have increased from 9.0% to 11.2% and although the proportion of female professors has risen form 3.9% to 5.5%, women in these top positions are still very much in the minority.

Given that women make up about 22% of UK physics undergraduates, is it too much to hope that in 15 or 20 years’ time women will also make up a fifth or so of physics professors?

Another intriguing statistic concerns the highly international level of UK physics, particularly among women. According to the report, the proportion of female staff at UK universities who are not from the UK has risen from 46% in 2003/04 to 51% in 2009/10. This is much higher than the fraction of male non-UK nationals at UK universities, which has gone up from 31% to 40% in the same period.

Overall, across both men and women, the biggest proportion of non-UK staff working in UK physics departments come from Germany, followed by Italy, the US, China, Russia, France, India, Greece and the Netherlands. Make of that what you will.

You can read the full report here.

By Hamish Johnston

Japan has announced that it will bid to host the International Linear Collider (ILC), which is expected to be the next big experiment in particle physics after the Large Hadron Collider at CERN. The Japanese press is saying that the particle smasher – which is expected to cost about $8bn and stretch for 40 km underground – could be built on the island of Kyushu.

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The word on the street is that either Japan, CERN located on the Swiss-French border, or Fermilab in the US will play host to the massive project. Physics World’s Margaret Harris was at Fermilab recently to find out what will become of the facility now that its premier collider – the Tevatron – has shut down. Margaret didn’t focus on the lab’s chances of bagging the ILC, but rather on the plethora of experiments that are ongoing or planned for the near future. Her article about the visit also includes a series of audio clips of Fermilab physicists describing their work.

So, do you think Fermilab is the place for the ILC? This week’s poll question is:

Where should the International Linear Collider be built?

At CERN (Europe)
At Fermilab (US)
In Japan
It should never be built

Have your say by visiting our Facebook page. And feel free to explain your vote, or suggest another location, by posting a comment on the poll.

In last week’s poll, we asked, “Do you believe that researchers will always view the scientific paper as the gold standard for sharing new results?”. 56% of you think that the scientific paper will endure, while the remaining 44% believe the paper will be replaced by other forms of communication. That’s hardly a ringing endorsement of something that has served science well for several centuries.

One thing that commenters could agree on is the importance of peer review in science communication. One voter, Robert Minchin, said “Peer review is far too useful, not just as a ‘gatekeeper’ for what gets into the literature, but also in preventing us from embarrassing ourselves: like most (if not all) scientists, I’ve had referees spot errors that I had been completely blind to.” He goes on to say that while the concept of a paper will endure, they “may not be anything like we have had in the past”. He added, “I would expect it to become standard for journal publishers to provide the ability to manipulate and search data tables, view them graphically, etc. as part of their value-added service.”

Another pollster, Jose Riera, agrees about the importance of peer review, writing: “The real question is peer-reviewed papers or not peer-reviewed. My answer is that only peer-reviewed papers could have some minimum standards or scientific value.”

Thank you for all your responses and we look forward to hearing from you again in this week’s poll.

The February 2012 issue of Physics World is out now

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By Matin Durrani


The February issue of Physics World magazine is now out, featuring some great articles that I think I ought to tell you about.

Physics comes to life – Mark Haw from the University of Strathclyde and Otti Croze from the University of Glasgow explore the strange world of swimming micro-organisms – and how it is having an impact on biology, biotechnology and fundamental physics.

Gallery of whispers – Oliver Wright from Hokkaido University in Japan looks at a little-known effect dubbed “whispering-gallery waves”. Dating back to the work of Lord Rayleigh at St Paul’s Cathedral in London, it appears throughout science in fields as diverse as astronomy, optics and acoustics.

Securing the future – John Womersley, chief executive of the UK’s Science and Technology Facilities Council, explains why the country’s research community needs to safeguard its own future.

Careers, interrupted – Jan West describes the work of the Daphne Jackson Trust, which has helped more than 200 people to return to working in science after a career break.

Don’t miss either Rick Trebino’s Lateral Thoughts article “Fire in a crowded theatre”, while over in news and analysis, we have an interview with Italian theorist Giorgio Parisi entitled “The Italian activist” and an update on the work of the SESAME synchrotron being built in the Middle East. Plus enjoy Margaret Harris’s feature “Fermilab’s next frontier” in all its glory.

Members of the Institute of Physics (IOP) can read the new issue free online through the digital version of the magazine by following this link or by downloading the Physics World app to your iPhone or iPad or Android device, available from the App Store and Android Marketplace, respectively.

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