The thermal Josephson effect, which occurs when heat is transported across a gap between two superconductors, has been measured in the lab for the first time. The experiment was done by two physicists in Italy and confirms a theoretical prediction made in 1965. As well as confirming the bizarre prediction that some heat flows from the cold side of the junction to the hot side, the breakthrough could further the development of thermal circuits that use heat in much the same way as charge is used in electronic devices.
The conventional Josephson effect was predicted in 1962 by the British physicist Brian Josephson and was observed in the lab less than a year later. The effect occurs in a Josephson junction, which is created when two superconductors are separated by a thin layer of non-superconducting material or free space. Josephson showed that Cooper pairs – paired electrons that experience no electrical resistance within superconductors – can tunnel across the junction. All of the Cooper pairs are in the same quantum state and are thus represented by the same wavefunction. The tunnelling current is a sinusoidal function of the phase difference of the wavefunction from one side of the gap to the other. As a result, a current of Cooper pairs will flow across the gap even if there is no applied voltage.
If a voltage is applied across the junction, then things get more complicated and three different processes affect how current flows across the junction. The first, predominant term is the Josephson supercurrent, which would be present even without the voltage. The second contribution is from Cooper pairs that break apart into their constituent normal electrons, which can then tunnel through the potential barrier under the influence of the applied voltage. Last, there is an “interference current” that arises from the interaction between the first two processes.
Thermal bias
In 1965 Kazumi Maki and Allan Griffin of the University of California, San Diego calculated what would happen if a Josephson junction were given a thermal bias – that is, one side being slightly hotter than the other – rather than the usual voltage bias.
Ordinary metals can transport heat by energetic electrons moving from hot areas to colder regions – where they heat the surroundings by scattering from atoms and creating lattice vibrations. This does not apply to superconductors, however, because Cooper pairs move without scattering. In a thermally biased Josephson junction, therefore, the supercurrent does not contribute to heat flow. However, both electron tunnelling and the interference current can be involved in heat transfer across a junction.
Heat flow from electron tunnelling is a straightforward process that will always move heat from the hotter to the colder side of the junction. The curious part of Maki and Griffin’s prediction, however, is that the interference current can sometimes carry heat from the cold to the hot side. This is because, like the supercurrent, it depends on the superconductor wavefunction.
Tough to test
Testing this prediction has proved difficult, according to Francesco Giazotto and María José Martínez-Pérez of the NEST Institute of Nanoscience and Scuola Normale Superiore in Pisa – who are the first to do so. This is because, unlike electric currents, heat currents cannot be measured directly. “There is no analogue of an ammeter for a heat current so you are measuring an observable that is related only to the heat current like temperature,” explains Giazotto. He also says that it is much more difficult to keep track of heat flow than of charge.
Giazotto and Martínez-Pérez made their measurements on a superconducting quantum interference device (SQUID) – a loop of superconductor broken by two Josephson junctions. One half of the loop is kept at a slightly warmer temperature, causing normal electrons to carry heat across the two junctions to the cooler side as predicted.
The experiment involves altering the amount of magnetic flux that passes through the SQUID, which in turn affects the nature of the wavefuntion at a Josephson junction. By showing that the heat flow modulates between maximum and minimum values as the magnetic flux is changed, Giazotto and Martínez-Pérez have confirmed that the interference current can actually transfer heat from cold to hot. However, the overall heat flow does not reverse because the flow is dominated by normal electrons tunnelling through the junctions.
“Very clean result”
Raymond Simmonds of the National Institute for Standards and Technology in Boulder, Colorado, is impressed by the experimental challenges the researchers have overcome. “It’s really surprising that they got to measure a very clean result,” he says. “They had to do some pretty good engineering to make their heaters and their thermometry well characterized, all on a very small device, and to engineer all their contacts to ensure the system isn’t shorted out by the substrate.”
Giazotto and his colleagues are now look at possible practical applications of the result could be. He speculates about the possibility of “a sort of coherent caloritronic circuitry – the analogy of electronics but with heat”. He suggests it might be possible, for example, to produce heat transistors or heat rectifiers or even to produce devices without an electronic analogue.
“What is temperature?” is the sort of question that a seven year old would ask – and a physicist would struggle to answer in a simple way. That’s why a paper published today in Science about “negative temperature” seems very puzzling at first glance.
One way of looking at temperature is as a way of describing how energy is distributed among a collection of particles. Most particles will have a small amount of energy and the probability that a particle has a higher energy will drop exponentially with energy – the familiar Maxwell–Boltzmann distribution of an ideal gas. Temperature times Boltzmann’s constant is the parameter that fits the distribution to experimental data. Implicit to this distribution is that there is a minimum energy (zero) and no maximum energy.
Now, a team of physicists has used ultracold atoms to create what is essentially a mirror reflection of this familiar scene – a system with a maximum energy and no minimum energy. Furthermore, the probability that a particle in this system has an energy approaching this maximum is very high and drops off exponentially as the energy decreases.
So if you interpret this in terms of the Maxwell–Boltzmann distribution, you get a negative temperature (or perhaps a negative Boltzmann’s constant).
Ulrich Schneider and colleagues at the Max Planck Institute for Quantum Optics in Munich created this system by using an ultracold quantum gas in which the individual atoms repel each other. In this system the atoms want to move apart from each other but are trapped by laser light.
The researchers then adjust the laser light to “freeze” the atoms into a state called a Mott insulator, in which the atoms are stuck in a solid-like lattice. The interaction between atoms is then flipped to be an attractive one and the trap is switched to an “anti-trap” – the laser light tending to push the atoms apart.
The researchers then return the atoms to the gaseous state. The anti-trap provides the maximum energy, to which most of the atoms push against as they try to get closer to each other. And, hey presto, the system behaves as if it has a negative temperature.
So have Schneider and colleagues ventured below absolute zero? No, but they have done a nifty experiment!
For those of you outside of the UK, or those who were not quite so firmly glued to the telly over Christmas, you may not yet have had the pleasure (or pain) of viewing Stephen Hawking’s latest dalliance into popular culture. Hawking is the chief protagonist in a new television advert for the price-comparison website gocompare.com, as part of the company’s “Saving the Nation” campaign. Playing the boffin hero, Hawking apparently does the UK a favour by ridding it of the character Gio Compario, an impassioned but unbearable comedy maestro who spends his days singing about the “go compare” brand. Compario meets his sorry end on a UK high street when he is sucked into a black hole created by the mischievous Hawking, who is seen grinning with glee at the outcome.
I was left with the mixed feelings of mild amusement and utter horror at the cheesiness of the advert, precisely as intended by its creators. The fact that I am even writing this post proves that the advertisers have achieved their objective, though I would hasten to add that I neither approve nor disapprove of the website – in fact, I’ve never even used it. A more interesting debate to me is whether – after all things are considered – the use of physics and a celebrity cosmologist in this advert are good things for science. On the one hand, it shows just how firmly established Hawking is in the public consciousness. I think it is fair to say that when it comes to popular culture, physics and geeky humour in general are enjoying a day in the sun at the moment. You just need to look at the popularity of a show like The Big Bang Theory and the growing appeal of science television presenters such as Michio Kaku and Brian Cox, not to mention Hawking’s cameo appearances in The Simpsons.
On the other hand, if you are not willing to suspend disbelief, you might start to nit-pick just a little about the plot of this advert. You might start to ask some terribly pedantic questions such as “How can it be that while Gio Compario is hoovered up by a black hole, the other people on the high street manage to miraculously escape it unharmed?”. On a more political note, you may also ask whether a man of Hawking’s talents should not be devoting his time to something a bit more meaningful. Though you could hardly accuse him of being the first celebrity to make a bit of cash thorough appearing in TV commercials.
Please tell us what you think by taking part in our first Facebook poll of the year.
Is Stephen Hawking’s appearance in this advert for a price-comparison website good for the communication of science?
Yes No
Let us know by visiting our Facebook page. And as always, please share your thoughts on the matter by posting a comment on the poll.
The 2013 Wolf Prize in Physics has been awarded to Juan Ignacio Cirac of the Max Planck Institute for Quantum Optics in Munich, Germany, and Peter Zoller of Innsbruck University in Austria for “groundbreaking theoretical contributions to quantum-information processing, quantum optics and the physics of quantum gases”. The duo will share the $100,000 prize, which will be presented by the president of Israel at the Israeli parliament (Knesset) in May.
Both Zoller and Cirac are key figures in the burgeoning field of quantum information, having, for example, devised several protocols for quantum communication based on entangling two or more ultra-cold atoms, as well as developed methods for quantum computing based on trapped ions.
“It is very exciting to receive one of the top prizes in physics, and even more so to share this award with Cirac, who has been a long-time friend and colleague,” Zoller told physicsworld.com. “I feel very lucky to have been working as a theorist in the field of quantum optics, which during the last 20 years has redefined itself by building interdisciplinary bridges to quantum information and quantum many-body physics.”
Cirac also told physicsworld.com that it is a “great honour” to receive the Wolf prize. “I think it is fair to say that [we] represent several scientists who have made many contributions to the field of quantum information – a field that is still progressing and attracting many different scientific communities,” he says. He adds much of the work was carried out in collaboration with other scientists and that the prize “also recognizes their work”.
The Wolf prize is awarded by the Wolf Foundation in Israel and is thought to be one of the most prestigious prizes in physics after the Nobel prize. The foundation was created in 1975 by Ricardo Wolf, a German-born inventor and diplomat.
By calculating the behaviour of protons and neutrons inside carbon nuclei from first principles, physicists in Germany and the US have identified the shape of carbon’s Hoyle state – which is an important step in the production of heavy elements inside stars. The researchers found the state to have an unusual bent structure, a finding that should help identify the forces at work in carbon production.
Carbon-12 comprises six protons and six neutrons and is a key step in nucleosynthesis – the process by which heavier elements are produced inside stars. Physicists studying stellar fusion in the 1940s and 1950s reckoned that carbon-12 forms when two helium-4 nuclei fuse to produce beryllium-8 – which then fuses with a third helium-4 nucleus. There was a problem with this hypothesis, however. The energy of the fused particles is considerably higher than that of the ground state of carbon-12. This implies that the new particle is in fact extremely unlikely to form in this way – far too unlikely to account for the great abundance of carbon in the universe.
According to Hoyle
To overcome this apparent contradiction the British astronomer Fred Hoyle proposed in 1954 that carbon-12 has an excited state that had never been seen before. The idea is that carbon-12 would form readily in this state and then decay to its ground state, giving off a well defined amount of energy (7.6 MeV) in the process. This excited state was then observed three years later by researchers at the California Institute of Technology, when carrying out experiments involving beta decays of boron-12.
For the past 60 years nuclear physicists have been trying to understand the nature of this “Hoyle state”, which is not predicted by standard nuclear models. These models regard nuclei as being made up of individual protons and neutrons, and it was reckoned that the Hoyle state is better described as three helium-4 clusters. Those clusters have now been identified by Ulf Meissner of the University of Bonn and colleagues, thanks to the number-crunching power of the JUGENE supercomputer in Jülich and a new form of Steven Weinberg’s “effective field theory”, which considers protons and nucleons as individual entities rather than as bound states of three quarks.
Space–time lattice
Weinberg’s theory reduces the number of particles that can be considered to make up a carbon-12 nucleus by a factor of three – from 36 to 12. Even 12, however, is too many for an analytical description of the nucleus. Instead, Meissner’s group combined the theory with numerical methods often used to describe the interaction of individual quarks via the strong force. This approach breaks down space and time into discrete chunks, constraining particles to exist only at the vertices of a space–time lattice and so radically simplifying the possible evolution of the particle system.
In a paper published in 2011, Meissner and co-workers described how they used this hybrid approach to identify the Hoyle state. To do this they first picked out carbon-12’s ground state, setting up vast numbers of configurations of the virtual protons and neutrons within JUGENE and then watching what happened as those configurations evolved in time. The configuration that lasted the longest, being the most stable, was the ground state. Identifying the Hoyle state was a bit trickier since it involved stopping the simulation at some earlier point in time and then disentangling the various states that remained. Despite the challenges of calibrating their simulation using scattering and other data, their calculated values for the energy of the carbon-12 ground state and the Hoyle state agreed very well with experiment.
“Bent arm” shape
Now in this latest work, the team has calculated the structure of those states using a more sophisticated representation of the nuclear wavefunction. Likening the nucleons and groups of nucleons to LEGO bricks, Meissner says that “before we had bricks of just one size and now we have a whole series of different-sized bricks that we can use to construct more complex structures”. Building up those structures, the group found that in the ground state, carbon-12 consists of three helium-4 clusters arranged in a compact equilateral-triangle formation, whereas in the Hoyle state the three clusters form an obtuse triangle or “bent arm” shape. This more open configuration, the researchers explain, results from the extra energy in the system.
One exciting aspect of the research, according to Morton Hjorth-Jensen of the University of Oslo in Norway, is that it should allow scientists to understand which part of the strong force dictates the carbon-12 decay. This is important because the force in fact consists of several elements, including some that deform the shape of nuclei. “Hoyle predicted his state on the basis of the anthropic principle, arguing that if the state didn’t exist we wouldn’t be here,” he says. “But we now want to understand the structure of this state in terms of its basic constituents and forces.”
Experimental tests
Meanwhile, David Jenkins of York University in the UK points out that the latest work makes a number of explicit predictions that could, in principle, be tested experimentally, including the existence of a number of electromagnetic transitions involving the Hoyle state. But he adds that these transitions are very weak and therefore hard to measure. “Such experiments will be no less challenging than the theoretical achievement,” he says, “but renewed effort is warranted given the strong topical interest.”
According to Meissner there is also more theoretical work to be done. One job, he says, is to reduce the spacings in their virtual lattice, in order to make more precise calculations. Another is to investigate larger nuclei, such as oxygen-16, as well as the reactions that give rise to these nuclei – in this case carbon-12 combining with a helium-4 nucleus. “This is a very important reaction in the sequence that generates life-giving molecules,” he adds.
Physics World will soon be publishing a feature article about the Hoyle state written by David Jenkins and Oliver Kirsebom, who is at TRIUMF in Canada.
Not stars, galaxies Each faint point on this sub-millimetre image taken by the Herschel Space Observatory is an entire galaxy. (Courtesy: ESA/SPIRE/Herschel-ATLAS)
I was the world’s first sub-millimetre astronomer.
This statement tends to irritate some of my colleagues, particularly those who had been lugging around sub-millimetre detectors to put on borrowed optical and infrared telescopes for a decade before I even became involved in the field. But it is true in the sense that I was the very first person to make observations with the James Clerk Maxwell Telescope (JCMT) on the day it opened for business on the summit of Mauna Kea in Hawaii 25 years ago. The JCMT was the world’s first dedicated sub-millimetre telescope, although it was not behaving itself on that first day, tending to drift away from wherever I pointed it.
There was also a much more fundamental problem faced by all sub-millimetre astronomers back then – there was simply no such thing as a sub-millimetre camera. All I had at my disposal was a single detector that could measure the strength of the sub-millimetre radiation only in the precise direction the JCMT was pointing, which on that day was not very precise at all. So to produce a sub-millimetre picture of the sky, I had to point the telescope in one direction and measure the strength of the radiation in that direction, before turning the telescope slightly and measuring the strength of the radiation in the new direction and so on and so forth. Painting by numbers, if you like.
About 10 years later, we did finally get a sub-millimetre camera, but it had only 37 pixels. That still left us well behind astronomers who work with visible light, for whom – even then – one million pixels were routine. (Of course, technology has now come so far that most mobile phones today have a camera that can record several megapixels.) It was only on 14 May 2009 that sub-millimetre astronomers finally caught up with their optical colleagues when the European Space Agency’s Herschel Space Observatory blasted off from French Guiana in South America. The observatory was named after the German-born astronomer Sir William Herschel, who discovered infrared radiation and the planet Uranus, with help from his sister Caroline.
Cool prospects
The sub-millimetre waveband, which consists of electromagnetic radiation at wavelengths between 100 μm and 1 mm, is the last waveband to be opened up for astronomy. It is the final electromagnetic frontier, if you will. One reason why sub-millimetre astronomers have lagged so far behind optical astronomers, who were after all taking pictures of the sky in Victorian times, is an embarrassment of riches. Virtually everything emits sub-millimetre radiation, whereas only very hot objects give off optical light. Optical astronomers therefore have it easy: to avoid the one object that gets in their way – the Sun – they just have to work at night.
Sub-millimetre astronomers, however, have to cope with the fact that everything around us emits floods of sub-millimetre photons. So the only way to detect faint signals from the sky without them being swamped by sub-millimetre radiation from the camera itself is to cool the camera down to less than one degree above absolute zero, which reduces the radiation from the camera to a minuscule level. The cameras on Herschel, for example, are cooled to 0.3 K using a large bath of liquid helium.
Another problem for sub-millimetre astronomy is that water vapour in the atmosphere absorbs this kind of radiation, which means that the technique can only be carried out from the tops of high mountains across just a handful of wavelengths that are free from water absorption. That was why, in the pre-JCMT period, astronomers had to perform heroic feats, transporting cumbersome cryogenic equipment to some very remote and inhospitable places, such as the summit of Mauna Kea, which lies more than 4000 m above sea level, where conditions are suitably dry. And when they were there, the sub-millimetre astronomers only had a short time to get their bolted-on kit working before the regular astronomers took over.
Herschel gets around the problem of moisture entirely by being located in space. In fact, it has the biggest mirror ever sent into space, some 3.5 m in diameter – larger even than that on the Hubble Space Telescope. But while Hubble circles the Earth every 90 minutes only 560 km above the surface, Herschel is at the second Lagrangian point, L2, some 1.6 million kilometres from us. It is one of five points at which a small object (Herschel) can remain stationary relative to any two much larger objects, in this case the Earth and the Sun. L2 is ideal for Herschel as it is so far from our planet, which is a beacon of sub-millimetre radiation.
1 Seeing new stars Sub-millimetre astronomy is perfect for studying star formation because stars are forged in dense clouds of dust and gas that warm up as they absorb the starlight, re-emitting it at sub-millimetre wavelengths. Just compare these images of the Andromeda galaxy. The optical image (left), taken with a 20-inch telescope, clearly shows Andromeda’s central bulge surrounded by a bluer star-forming disc. In contrast, the sub-millimetre image (right), taken by the Herschel Space Observatory, does not show the bulge at all but does reveal plenty of detail in the disc. The light comes from interstellar dust that hides the youngest stars from optical telescopes. (Courtesy: Robert Gendler; ESA/Herschel/SPIRE/PACS/J Fritz)
One of my favourite Herschel pictures reveals just why astronomers bother working with electromagnetic frequencies outside the traditional optical band (figure 1). It shows the Andromeda galaxy, which is one of the two big galaxies in the Local Group of galaxies – ours, of course, being the other. Andromeda is just visible with the naked eye, but if you view it with even a small optical telescope, you can see a bright, central bulge of old, red stars surrounded by a disc of much younger blue stars. In the Herschel image, in contrast, the bulge has vanished because stars emit hardly any sub-millimetre radiation. The radiation that Herschel is detecting in this image comes instead from tiny interstellar dust grains that are located in the outer disc, but not in the bulge. These grains emit sub-millimetre waves because they absorb starlight and get heated to temperatures of about 30 K.
These grains are a huge problem for optical astronomers because they act like smoke – scattering and absorbing optical light. This interstellar smoke is thickest in the big gas clouds in which new stars are being born – so the bright ring in the Herschel image of Andromeda confirms the notion that stars in this galaxy are being born in the disc but are no longer being created in the inner bulge. Although the optical image shows some of the light from these newly formed stars, there are many more that are hidden by dust when viewed with an optical telescope.
Dust grains are basically not that interesting, except to the small group of astronomers who are absolutely passionate about the physics and chemistry of these tiny particles. (I’m not joking – some of my best friends are mad about dust.) Most astronomers, instead, are more interested in dust grains for what they might conceal. The classic example is the Horsehead nebula (figure 2), which is typical of the kind of place that William Herschel himself thought might be “holes in the heavens” with genuinely no stars. We now know, however, that these “holes” are just places where dust is in fact hiding the stars beyond.
2 Dust busters The Horsehead nebula – seen at optical wavelengths (left) by the European Southern Observatory – is the kind of place that was once thought to be a “hole in the heavens” that did not have any stars. In fact, these holes are just places where dust is hiding the stars beyond, as can be seen from this sub-millimetre image taken by the James Clerk Maxwell Telescope (right). The light comes from dusty, star-forming regions – notably the place in the horse’s “throat”, where the dust is particularly dense. (Courtesy: Joint Astronomy Centre/Derek Ward-Thompson; ESO-ODT/Cyril Cavadore)
Interestingly, the sub-millimetre picture of the Horsehead taken with a camera on the JCMT by my Cardiff University colleague Derek Ward-Thompson shows that the horse appears to have “swallowed” an object that now lies stuck in its “throat”. The object is a place in the nebula where the dust is particularly dense and new stars are being born. Light from the young stars is heating the dust, which increases the amount of sub-millimetre radiation it produces.
Seeing the birth of stars
This ability to find and study newly formed stars, which are born in dense clouds of dust and gas, is one of the reasons why Herschel was launched. Quite simply, it would be impossible to study the first moments in the life of a star with a conventional optical telescope like Hubble because all that dust gets in the way. In peering into the big clouds of gas and dust that are the “maternity wards” of stars and then detecting the sub-millimetre light emitted from the dust around the newly formed stars, Herschel is therefore doing much to study star formation, which is one of astronomy’s “big questions”.
Indeed, Herschel has already taken a major step forward in showing how low-mass stars like the Sun were formed. Figure 3 shows pictures taken by Herschel of two of these stellar maternity wards, which exist as big clouds of gas and dust in a ring called the Gould Belt roughly centred on the Sun. Taken by a large international team led by Philippe André in Paris and including my colleagues in Cardiff, these pictures are actually pseudo-colour images made by combining three Herschel images taken at different wavelengths. The colours reveal the temperature of the dust, with red indicating cold dust and blue showing warm dust.
3 Blue is the colour The Herschel Space Observatory has been able to tell astronomers a lot about how low-mass stars like the Sun were formed. On the left, for example, is a sub-millimetre image of a cloud of dust and gas known as the Aquila Rift, created by combining three separate Herschel images. The colours indicate the temperature of the dust, with the blue regions being hot spots where the dust is heated by newly formed stars. A similar image of a different cloud known as the Polaris Flare, however, has only one colour, which indicates that its dust is all at exactly the same temperature and so has no newly formed stars. (Courtesy: ESA/SPIRE/PACS/P André for Gould Belt Survey; ESA/SPIRE/PACS/P André for Gould Belt Survey and A Abergel for EID Survey)
The picture of one of the clouds, the Aquila Rift, which is about 750 light-years from Earth, is a coruscating colour-drenched image that looks remarkably like a painting of a sunset on a stormy evening by William Turner in one of his more exuberant moods. The picture of the other cloud, the Polaris Flare, which is about 500 light-years away, is a monotonous brown. The explanation for the differences is that stars are being born in the Aquila Rift but not in the Polaris Flare. The full palette of colours for the Aquila Rift shows that the dust has a range of temperature, with the blue and yellow “paint drops” revealing warm spots heated by newly formed stars. In contrast with this Turneresque image, the monochrome image of the Polaris Flare shows that all the dust is at exactly the same temperature, and thus that there are no newly formed stars.
But why are stars being formed in one cloud but not the other? The answer appears to lie in the properties of the streaks of dust and gas, known as filaments, that snake across all the Herschel images of clouds in our galaxy, which can probably best be seen in the picture of the Polaris Flare. There appears to be a critical mass density of about five solar masses per light-year of filament length, above which – as in the Aquila Rift – gravity causes the filaments to collapse to form protostars that appear as beads on the filaments. Below the critical value, as in the Polaris Flare, the filaments never collapse and no stars are born.
But what causes the filaments to form in the first place? A clue appears to lie in the recent discovery by the Gould Belt team that while the density of the filaments can vary wildly, their width – no matter where they are seen in the galaxy – is always very similar, being about one third of a light-year. Remarkably, the team thinks it can explain this by turning to some simple physics of the turbulent interstellar gas. According to its model, the gas is usually flowing faster than the speed of sound in the gas, but when it slams into a big cloud of stationary gas, it slows down to below the speed of sound to form a filament. Indeed, the model says the gas piles up in exactly the way seen in the filaments.
This explanation is what simple physics suggests, but remember that astronomers are not working in a laboratory so it is rarely possible for us to “prove” anything. The best we can usually do is to find a model that fits our observations.
Another of astronomy’s big questions concerns how galaxies are formed. One of the big discoveries made 15 years ago with the first sub-millimetre camera on the JCMT was that there are some galaxies in the early universe that are so shrouded in dust that they are emitting 1000 times more radiation in the sub-millimetre waveband than at optical frequencies. Indeed, they are such luminous sub-millimetre sources that the dust must be hiding a very large number of newly formed stars. Calculations suggest that the stars are being created so quickly that an entire galaxy could be made in barely 100 million years, or about 1% of the age of the universe. These luminous sources therefore almost certainly hold a clue to how galaxies were formed.
The future is bright
Sub-millimetre astronomy is advancing at a quite astonishing pace. Just 15 years ago when astronomers started using the first sub-millimetre camera on the JCMT, it would take a whole night to find a single one of these shrouded galaxies. The top image above, which was the first taken by my team shortly after the Herschel Space Observatory was launched, took only 16 hours to make and reveals 7000 dusty galaxies – from those that are nearby to others that are so far out in space that we are looking 10 billion years back in time.
Unfortunately, the 2160 litres of liquid helium that Herschel originally contained will finally run out in March this year. When that happens, the cameras will warm up, and the telescope will become just another piece of space junk among millions of other bits of rubbish now floating in space. However, the treasure trove of Herschel data will be picked through by astronomers for years to come.
Meanwhile, a new sub-millimetre telescope – the Atacama Large Millimeter Array (ALMA) – has started operation 5000 m above sea level in the remote and inhospitable Atacama Desert in central Chile. Although ALMA can only operate in atmospheric windows at a few wavelengths, its advantage over Herschel is that it has much higher angular resolution. ALMA will therefore be able to produce detailed pictures of the galaxies that only appear as little blobs to Herschel. It is likely that ALMA’s observations of the sources detected in the Herschel surveys will be the key to providing answers to the origin of both stars and galaxies. William and Caroline Herschel would have been proud.
I made that: The child-friendly home experiments in The Ultimate Book of Saturday Science are clever but surprisingly complex. (Courtesy: Shutterstock/kavring)
Ingenious ideas
The scene: a grey Saturday in January. The problem: post-holiday blahs. The solution? Well, how about making a clock out of paperclips? Or a combination helicopter and elevator? What about a cannon that shoots carrots, a four-foot-tall set of dominoes or a rocket railroad? The Ultimate Book of Saturday Science contains instructions for all of these projects, plus 67 others, from the ingenious mind of industrial scientist and author Neil A Downie. A few of the experiments, such as the vacuum bazooka, require only common household objects (perhaps supplemented by the local DIY store) and could be built by children with minimal adult help. Most, however, require more specialized components, including motors, power supplies, lenses and chemicals (and that’s just in the first chapter, which is devoted to “simple but subtle” projects). Indeed, many of the book’s experiments are best tackled with the help of a teacher, science-club mentor or family member with access to a half-decent electronics workshop. The rocket railroad, for example, is a fairly complex piece of equipment, and the assembly instructions are probably not detailed enough for children or mechanical novices to follow. Another project, a musical instrument called a Heliracket, is a little simpler, and looks like more fun than a barrelful of puppies – but you’ll need a supply of helium gas, multiple space hoppers and an ocarina (!) to make it. The bottom line is that most of these “Saturday science” experiments are going to require a fair amount of planning on the preceding Thursdays and Fridays. However, those willing to put in the effort will get a real kick out of this book.
2012 Princeton University Press £19.95/$29.95pb 576pp
Ingenious ideas, junior version
For kids who like building stuff, but aren’t yet old enough to whip up their own armour-piercing carrot cannons, Caroline Alliston’s two Technology for Fun books offer a gentler introduction to science experiments. The first book contains 30 “design and make” projects that many primary school children will be able to build on their own, using little more than office supplies, basic woodworking tools and the contents of a recycling bin. A good example is a “zip wire” for teddy bears, which features a pulley made from a wooden skewer, two CDs and the tops of milk bottles. The 14 experiments in the second book are slightly more complex, and require a basic suite of electronic components, including batteries, leads and a couple of different types of motors. If your house’s junk drawer lacks any of these things, the books’ website, www.technologyforfun.co.uk, lists a few companies that can supply parts for projects such as a paddle-powered toy boat and an electric paper-dart launcher. The science behind these contraptions is not explained in much detail, but the books are a good starting point for younger experimentalists.
2012 Alliston Publishing £5.00pb 58pp
Scepticism for beginners
Electroconvulsive therapy sometimes helps people with severe depression, but we don’t know why. There is no evidence that homeopathy works, or that the MMR vaccine causes autism. Most chiropractic treatments do not work either, although for some types of back pain, they may be as good, or bad, as conventional medicine. On the other hand, humans really have walked on the Moon, we really are contributing to climate change, and we really do share a common ancestor with monkeys. These, in brief, are the messages of Darryl Cunningham’s Science Tales: Lies, Hoaxes and Scams, a graphic novel about “controversial” scientific topics that arguably should not be controversial at all. Cunningham’s book is not specifically aimed at children or young adults, but his simple, clear prose and clever illustrations – which mix pen-and-ink cartoons with photographs and reproductions of newspaper headlines – make it particularly well suited as a beginner’s guide to the scientific method.
2012 Myriad Editions £11.99hb 176pp
Fusion goes on tour
Plasma physicist Melanie Windridge spent a lot of time on the road in 2010. As the Institute of Physics’s official Schools and Colleges Lecturer that year, she travelled all over the UK, giving talks about nuclear fusion to students at 35 different schools. She also blogged about her experiences, and these blog entries form the basis of Star Chambers: the Race for Fusion Power. Clearly written and lavishly illustrated, the book combines explanations of fusion physics with brief glimpses of the author’s life on the road, and its 130 pages are speckled with diagrams, photos and data from actual fusion experiments. There is even a “movie” of sorts, thanks to some cleverly placed time-lapse photos. The author’s on-the-scene anecdotes of bad weather and occasional tourist jaunts seem better suited to a regularly updated blog than a static book published two years after the fact. However, if Star Chambers helps bring Windridge’s travelling tokamak tale to a wider audience, this is surely a good thing.
Hello everybody and welcome back to Physics World after the festive break.
If you’ve just got your hands on a brand new tablet device, the first thing you’ll want to do – apart from reading the latest issue of Physics World magazine, of course – is possibly to use it to write your latest scientific paper using every physicist’s favourite typesetting language – LaTeX.
Not so fast!
Unfortunately, making LaTeX function on a tablet device has been no easy task, as software developer Duncan Steele makes clear in a fascinating feature article in the January 2013 issue of Physics World. Thankfully, LaTeX is making the switch to tablets, but it’s not been plain sailing.
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. It’s the start of the year – so why not join now?
Also in the January issue we look at promoting scientific entrepreneurism in the developing world, explore the new view of the universe as seen by the Herschel Space Observatory, find out how to eradicate experimental bias in science – plus much more besides.
For the record, here’s a rundown of highlights of the issue:
• Italy cancels €1bn SuperB collider – Michael Banks examines the repercussions of Italy’s decision to axe a new particle collider that would have produced copious amounts of B mesons
• Fuelling innovation in Africa – Joining a team of entrepreneurs and technology-transfer experts in Addis Ababa, Joe Winters asks what role physics has to play in the economic growth of one of the world’s poorest nations
• Identity physics – Robert P Crease calls for your new metaphors exploiting the Pauli exclusion principle and Bose–Einstein condensation
• The blind physicist – Physicists might not like to admit it, but preconception and bias taint many of their experiments. Brian Clegg explores how this “experimenter bias” manifests itself, and looks at the measures some collaborations are taking to counter its effects
• The revolution will be typeset – As the computing world shifts from desktops and laptops to tablet-style devices, one of the most widely used tools in physics – LaTeX – is struggling to follow. Software developer Duncan Steele explains how this typesetting program is now starting to catch up
• Cool dust and baby stars – The helium that is cooling its camera is about to run out, but the data from the Herschel Space Observatory, which is designed to study how stars and galaxies form, is likely to keep sub-millimetre wavelength astronomers busy for years to come. Steve Eales explains
• Fuelling the thorium dream – Jess Gehin reviews Superfuel: Thorium, the Green Energy Source for the Future by Richard Martin
• A clean solution – Michael Duncan, John Girkin and Tom McLeish describe how an unusual cross-disciplinary collaboration between Procter & Gamble and Durham University is generating benefits for both sides
• Once a physicist – Meet Ted Hsu – member of parliament for Kingston and the Islands, Canada
• The carbon-neutral gym – Michael de Podesta wonders whether gym-goers could actually make a difference to the environment
Rocky exoplanets orbiting some Sun-like stars in the Milky Way galaxy could be hotter and more geologically active than Earth and its solar-system companions, according to researchers in the US. The team looked at the abundance of radioactive elements such as thorium, which heat the interior of planets as they decay and thereby play an important role in how planets evolve. The team concluded that planets that are richer in thorium than Earth could be good candidates for the development of life – making them targets for study by astrobiologists and exoplanet hunters.
The research was done by Cayman Unterborn and colleagues at Ohio State University, who used data gathered by the European Southern Observatory’s High Accuracy Radial Velocity Planet Searcher (HARPS) spectrometer in Chile. The team focused on “solar twins”, which are stars that resemble the Sun in terms of their ages, sizes and general make-up. By looking at the abundances of radioactive elements potassium, thorium and uranium within these stars, the team was able to infer the compositions of any rocky exoplanets that may be orbiting the stars. In particular, exoplanets orbiting a star with more thorium than the Sun, for example, would be likely to contain more thorium than the planets in our solar system.
Scattered around the galaxy
Of the eight solar twins studied so far, seven display far higher concentrations of thorium than the Sun. “It all starts with supernovae,” explains Unterborn, who led the study. “The elements created in a supernova determine the materials that are available for new stars and planets to form. The solar twins we studied are scattered around the galaxy, so they all formed from different supernovae. It just so happens that they had more thorium available when they formed than [the Sun] did.”
On terrestrial planets such as Earth, plate tectonics is partially driven by heat produced in the mantle by the decay of radioactive elements. “The core is hot because it started out hot, but the core isn’t our only heat source. A comparable contributor is the slow radioactive decay of elements that were here when the Earth formed,” explains Wendy Panero at Ohio State.
On Earth, most of this heat comes from uranium. However, thorium has a longer half-life than uranium and the potential to produce more energy – and therefore thorium acts as a greater and more prolonged heat source. Planets with higher concentrations of this element would therefore not only be hotter, but would also stay that way for longer – leading to more dynamic and longer-running tectonic activity.
Recycling and replenishing
It is believed that plate tectonics might play an important part in maintaining the presence of water on a planet’s surface – along with recycling and replenishing the other chemicals needed to support basic life. Unterborn and colleagues therefore believe that any planets around these thorium-rich solar twins might be more likely to host alien life than if they were orbiting the Sun. Furthermore, longer-running plate tectonics could also mean that life on such planets would have more time to develop than here on Earth. In addition, the extra heat from the thorium could mean that the habitable zone – the range of planetary orbits in which life could exist – of such stellar systems could be larger than that of our solar system. “If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars,” says Unterborn.
“Across the galaxy, it makes sense that natural variation would exist in the amount of radioactive elements inside stars like ours,” comments Kathleen Campbell at the University of Auckland, New Zealand. “It is exciting to think we can remotely estimate the size of a solar system’s habitability zone, with the implication that there could be more opportunities for life to take hold amongst its suite of terrestrial inner rocky planets.” But she also points out that what is unclear from this study, however, “is why [the] longer-lived existence of plate tectonics would necessarily give more time for life to arise, since it arose quite early in Earth’s history. A key seems to be the presence of water, in liquid or solid form”.
Early stage
“At this point, all we can say for sure is that there is some natural variation in the amount of radioactive elements inside stars like [the Sun],” cautions Unterborn, as the results are at the preliminary stage. “With only nine samples including the Sun, we can’t say much about the full extent of that variation throughout the galaxy.” For Unterborn, who presented these results during last week’s meeting of the American Geophysical Union in San Francisco, the research continues. Planned developments include further analysis of the HARPS data to improve the accuracy of the computer models used in this study, as well as searching for more solar twins for comparison.
Historians of physics will surely remember 2012 as the year when the Higgs boson – or a particle that looks very much like it – was finally discovered at the Large Hadron Collider (LHC) at CERN. Indeed, it should come as no surprise that the discovery was picked by us as the Physics World Breakthrough of the Year for 2012. The choice was an obvious one – too obvious perhaps – but it was one that we could hardly have overlooked. Yet for anyone who fears that Physics World is obsessed with particle physics – no, we’re not: the rest of our top 10 breakthroughs include everything from optics and astronomy to energy harvesting and the spooky properties of “twisted” light.
But what will happen in the world of physics in 2013? What will be the key discoveries of the year, who will make them and where? The beauty of physics, of course, is that no-one knows for sure. But that hasn’t stopped us here at Physics World from gazing into our (quasi) crystal ball and making our predictions for what we think will happen next year, what might take place – and what definitely won’t. One thing is for sure: we will be here to cover the world of physics next year.
Shut down and calculate
Over at CERN, physicists can expect a busy start to the year as they capture their final data from the LHC – in the form of proton and lead-ion collisions – before the collider enters a scheduled 24-month shutdown, starting on 11 February. Teams of engineers will then begin the lengthy business of fixing about 1000 defective interconnects so that the collider’s magnets can operate closer to their target bending field of 8.3 T, which ought to allow the LHC to collide particles with a total energy of at least 13 TeV starting in 2015.
The down-time in 2013 will give physicists a breather as they comb through the existing LHC data, which has been spewing out at a rate of several gigabytes per second in recent months. You can therefore expect to see a further flurry of papers about the properties of the new boson being written and then immediately dissected on blogs by the likes of Adam Falkowski, Phillip Gibbs, Matt Strassler and Peter Woit. However, we predict that firm signs of supersymmetry – the theory that could unify the weak, strong and electromagnetic forces at energies of about 1016 GeV – will be few and far between in 2013. Sorry, SUSY-lovers.
For those who are interested, CERN has a fascinating dashboard that anyone can view to keep track of the LHC’s current status. Although the collider will be down for most of 2013, we predict further debate among CERN staff in the coming year over when exactly – or even if – the LHC will be able to reach its top design energy of 14 TeV. CMS spokesperson Joe Incandela told Physics World last week that the current plan is “to ramp up to 13 TeV in the next run after the shutdown” but that going higher will be “not so practical” for the experiments. The problem, it seems, is that to get from 13 TeV,to 14 TeV, the magnets would have to be warmed up, cooled down again and then “retrained”, which takes a long time. “I believe that they will stay at 13 TeV at least for an initial meaningful period to allow us to have a decent consistent dataset,” notes Incandela.
Another matter of contention in 2013 will be which particle physicists – if any – will bag the year’s Nobel Prize for Physics
Another matter of contention in 2013 will be which particle physicists – if any – will bag the year’s Nobel Prize for Physics. Nominations for the prestigious award close at the end of January and Peter Higgs is surely a shoo-in for predicting the existence of the particle that bears his name. However, the members of the Royal Swedish Academy of Sciences will have a tough choice deciding which two other people (it can only be two) should share the prize with him. Other theorists? Or some combination of LHC scientists, such as some of the seven who earlier this month shared the new $3m prize from the Russian physicist-turned-entrepreneur Yuri Milner’s Fundamental Physics Prize Foundation?
It is a messy business because, as Higgs himself pointed out in an audio interview with Physics World last year, at least five other theorists – (the late) Robert Brout, François Englert, Gerald Guralnik, Carl Hagen and Tom Kibble – deserve credit for predicting the Higgs boson, and possibly Philip Anderson too. Our prediction is that the Nobel wonks will, after much agonizing, award the prize to Higgs, Englert and Anderson. (Brout, who previously shared the Wolf prize in 2004 with Higgs and Englert, died in 2011.) But with the Nobel-prize pot having shrunk by 20% this year to about $1.1m, Milner’s new $3m is likely to take even more of a centre stage next year.
Away from particle physics, there are some interesting astronomy and space-science missions set for launch in 2013. They include China’s first ever lunar rover – Chang’e 3 – as well as a NASA mission (LADEE) to gather information about the Moon’s surface and its dust, which could be useful data for anyone planning to set up a lunar base. NASA will also launch one craft (MAVEN) for studying the Martian atmosphere and another (ISIS – postponed from 2012) for probing the corona and solar wind.
Not to be outdone, the European Space Agency (ESA) has its own launch programme, which includes the Sentinel-1 Earth-observation craft, its Gaia star-cataloguing mission, and a constellation of three satellites in different polar orbits, known as Swarm, to monitor the Earth’s magnetic field (also held over from 2012). Continuing the US’s shift towards commercial space transport in the wake of the retirement of its space-shuttle programme, 2013 should also see two further missions to the International Space Station from SpaceX and a demonstration flight by the Orbital Sciences Corporation of its Cygnus spacecraft, which will also aim to reach the ISS.
Over in cosmology, 2013 will be the year when bucketloads of new data about the early universe emerge from ESA’s Planck mission, with the start of April seeing a major meeting in the Netherlands at which researchers will take an in-depth look at its initial scientific results. These scientists will be able to get their hands on “temperature maps” of the whole sky at nine different frequencies, which will reveal more details of the anisotropies of the cosmic microwave background. The maps will also provide fascinating new information about everything from the Milky Way to the energy “kick” given to CMB photons passing through the hot gases of large galaxy clusters – what is known as the Sunyaev–Zel’dovich effect. And for all you amateur astronomers out there, keep an eye out for next November, when a newly discovered “supercomet” called ISON, some 15 times brighter than the Moon, could cross the night sky in spectacular fashion.
But next year, as always, most physicists will do work that is much smaller in scale and, dare one say, be more practical and relevant to the real world than anything in astronomy, particle physics and cosmology. Unfortunately, it is always harder to say what the breakthroughs in such fields will be, but you can certainly expect plenty of eye-popping advances in metamaterials, graphene, cold-atom research and quantum communication and computation, to name but four.
Tight science funding will continue to weigh heavily on physicists’ minds in 2013, as it does every year. In tough economic times, some countries will come to the narrow-minded conclusion that investing in science is a luxury they can ill avoid and scientists in these nations will have a job on their hands persuading politicians to defend their corner. But strong funding for science is, in fact, an essential tool in boosting growth, with Germany, for example, having recently decided to increase its science budget in 2013 by 6%.
And although not everything has plain sailing in the US for funding in recent times, America has been fortunate in having Steven Chu – a physicist and a Nobel laureate to boot – making a strong case for science as President Obama’s energy secretary for the last four years. But serving for so long as head of the US Department of Energy is a tough gig and we predict that Chu, 64, will find the attraction of his cold-atom lab bench simply too hard to resist. A reshuffle of other top science jobs is likely too as Obama picks his new administration.
And with money – or the lack of it – to the fore, you can be sure that some physicists will continue in 2013 to press for fundamental changes to how scientific journals are published. Many researchers cannot see any justification for why they have to pay for the privilege of reading journals containing papers they have written, done the research for and peer reviewed. The coming year will therefore see a further push for “open access”, whereby papers appear in free-to-read repositories or in journals that have no subscription fees.
Unfortunately, the transition to open access will not be easy, not least because the traditional peer-reviewed journal paper is the “unit of currency” for a successful scientific career and has served the sciences so well for hundreds of years as a powerful means of communication. Moreover, running journals is an expensive and time-consuming business – managing the peer-review process, running IT systems and making papers findable does not come cheap – and these costs have to be met from somewhere.
We can therefore expect to see journals publishers busily devising new strategies that can let their publications, which after all often act as a nucleus for the development of new fields, survive in this changing environment. Learned-society publishers such as IOP Publishing, which publishes Physics World, will be hoping that such strategies succeed, not least because the profits they make go directly back into supporting the efforts of the scientific community.
Time for celebration
As for notable scientific anniversaries, physicists will in 2013 be able to celebrate the centenary of Niels Bohr’s simple model of the atom, which used quantum ideas to predict the frequencies of light emitted by excited hydrogen – something that was impossible with classical physics alone. The coming year also marks the 100th anniversary of Lawrence Bragg’s publication of his eponymous law concerning X-ray diffraction from crystals, as well as the centenary of Robert Millikan’s measurement of the charge on the electron, Frederick Soddy’s coining of the term “isotope”, and Hans Geiger’s realization of the link between atomic number and nuclear charge.
Closer to home, 2013 marks Physics World‘s own 25th anniversary. We will be celebrating with a special issue of the magazine in October, along with some other initiatives throughout the year, so watch this space for more details of our year-long celebrations. And in addition to the regular monthly edition of Physics World, which is available free to all members of the Institute of Physics, we will also be publishing a series of five focus issues on optics and lasers (April), nanotechnology (June), vacuum technology (August), big science (October) and medical imaging (December), as well as a special report on physics in South Korea (September).
And, as always, this website will offer our regular coverage of the latest physics research, selected features from our magazine, as well as our quarterly books podcasts and video reports from the world’s leading physicists and physics labs. So, whatever 2013 has in store for physics – and hopefully no more cringeworthy Gangnam-style spoof Higgs videos – keep coming back to stay up to date. In the meantime, we wish you all the best for 2013 – and see you in the new year.
Happy with our predictions? Annoyed at something we missed? Tell us what you think by commenting below.
