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What do you think has been discovered on Mars by NASA's Curiosity rover?

By James Dacey

Facebook poll

Speculation has been running wild this week after NASA scientist John Grotzinger told National Public Radio (NPR) that the agency’s Curiosity rover has helped uncover a “major” discovery about Mars. The mission is part of NASA’s Mars Exploration Programme, which has a goal of determining whether life has ever arisen on Mars. Given that Grotzinger is the chief scientist of the Curiosity mission, people are naturally getting excited.

In the interview, broadcast on Tuesday, Grotzinger was talking with enthusiasm about the results coming in from Sample Analysis at Mars (SAM), a suite of instruments aboard the rover designed to collect soil and atmospheric samples. “We’re getting data from SAM,” he said. “These data are gonna be one for the history books. It’s looking really good.” Grotzinger said that the mission scientists are eagerly analysing the data but that we should not expect an announcement for several weeks.

So when these findings do become public, what will they reveal? Let us know what you think by taking part in this week’s Facebook poll.

What do you think has been discovered on Mars by NASA’s Curiosity rover?

Conditions favourable for life
Evidence to suggest that life has never existed on Mars
A microscopic fossil
A living micro-organism
Something else (please share your suggestions as a comment)

To take part in the poll, please visit our Facebook page..

In last week’s poll we looked at the issue of physics education. We asked whether you believe that 16–18 year olds should be taught modern physics such as quantum mechanics? The question was inspired by the publication last week of an open letter to President Barack Obama lamenting state education in the US. The letter, in the form of a YouTube video, was bemoaning the fact that current curricula in the US focus almost exclusively on classical physics while excluding modern physics such as quantum mechanics almost entirely.

The poll had a lot of responses on Facebook, with 67% of respondents believing that these students should be exposed to quantum mechanics – but only the ideas not the complex mathematics. 28% disagree and believe that the students should be exposed to the “whole shebang”, including the maths. The remaining 5% believe that at this age, physics students should focus exclusively on classical principles.

Interestingly, the majority of comments that accompanied the poll came from the small group of people that believes that students should remained focused on classical physics. One respondent, David Peter Wallis Freeborn, wrote “There’s no point in teaching the maths of QM at the age of 16–18. They won’t have mastered linear algebra or any classical mechanics. You have to teach things from the base up, not just rush straight to ‘interesting’ modern theories.” Another commenter, Kristian Dominek Barajas, has a similar opinion: “My main concern is that students aren’t being engaged with the already complex and difficult topics in classical physics, which will ultimately stunt their growth in the field.”

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

Single fibre sees where no endoscope has gone before

An endoscope made from a single optical fibre just 200 μm thick has been made by researchers in South Korea and the US. The device offers the possibility of imaging parts of the body where no endoscope has gone before; in addition, its powerful image-processing algorithms may also allow the device to take holographic images. While the method currently has several drawbacks – it will not work if the fibre is bent significantly, for example – it could find use in a number of medical-imaging applications.

Endoscopy is a widely used medical procedure that involves a thin – and often flexible – tube being inserted into the body to obtain images of internal tissue. The fibre carries light into the body and then back out again. Although there are several different types of endoscope, they all need to have a way of illuminating the tissue of interest and a way of transmitting the image outside of the body. In situations involving very delicate tissues, making the endoscope as thin as possible could offer medical benefits.

In principle, an endoscope could be made from just a single optical fibre, so that a fibre with a 200 μm diameter, say, would be able to collect and transmit an image that covers a 200 μm-diameter circle on the subject. The problem with using just a single fibre, however, is that some of the light travelling down the fibre would be scattered by defects and get distorted beyond recognition. But what Wonshik Choi and colleagues at Korea University in Seoul have now done – together with researchers at the University of Pennsylvania and the Massachusetts Institute of Technology – is to find a way of characterizing these scattering processes and using this information to reconstruct the image.

Keeping track of scattering

Before a single fibre is used as an endoscope it has to be calibrated outside the body by firing a laser into one end of the fibre and measuring the brightness and phase of the light that emerges at the other end using a special camera. This process is repeated over a range of incident angles, with the resulting data being used to create a “transmission matrix” that describes how light makes its way through the fibre.

Although this matrix is enough to reconstruct an image that emerges from the fibre, the problem when the endoscope is used inside the body is that the tissue is illuminated by a laser beam sent down the fibre. This light also scatters, meaning that the tissue is illuminated with a “speckle” pattern of light and dark patches. So to ensure that the tissue is fully illuminated, the incident angle of this laser also has to be varied – effectively scanning the speckle pattern across the tissue.

Holographic bonus

One bonus of obtaining multiple data over a range of incident angles is that the information can be used to build up a holographic image of the tissue without having to scan the tip of the fibre. The team tested the method by showing that it can resolve a standard test pattern that contains a series of shapes, some as small is 2.2 μm across. The researchers then used the set-up to image the intestine tissue of rats, where they were able to use holography to study 3D structures in the tissue.

Low-cost endoscopes could be life-savers in developing countries
Allard Mosk, University of Twente

One important drawback of the endoscope – according to Choi – is that the fibre cannot be bent significantly from the shape at which the calibration was performed. As a result, the endoscope must be rigid – and not able to take full advantage of the fibre’s flexibility. Choi told physicsworld.com that the team is therefore exploring several solutions.

“The most promising approach, in my opinion, is the in situ calibration of the fibre,” he says. This involves injecting the fibre into the tissue while allowing it to bend. The transmission matrix for that specific curvature would then be obtained by firing a laser beam down the fibre measuring the light that reflects back up the fibre from the inner surface of the fibre tip.

Diagnosing disease

The team is also developing a rigid endoscope and Choi says that in addition to its extreme thinness, the device can obtain images with higher spatial resolution than existing instruments. “We can attain a resolution below 1 μm and this this will facilitate in vivo disease diagnosis,” he says.

Allard Mosk of the University of Twente in the Netherlands believes that an important advantage of Choi’s endoscope is that it combines a simple design with computer processing. “Using a computer to correct for the optical distortions is very much cheaper when mass produced than making high-quality optical endoscopes,” he explains. “Low-cost endoscopes could be life-savers in developing countries,” he adds.

Mosk and colleagues have recently developed a way of obtaining images through biological materials that are normally opaque to light. Their technique also involves scanning speckles across an object and Mosk suggests that it could be combined with the endoscope to allow for an even clearer view – particularly when the tip cannot be brought right up to the tissue of interest and the light passes through intervening material.

The endoscope is described in Physical Review Letters.

Soft matter’s charismatic pioneer

This summer I took a break from lecturing at a graduate training school in Boulder, Colorado, to attend a talk by the soft-condensed-matter physicist David Weitz. His lecture was about colloids, and in the middle of it, he began to reminisce about the field’s early days. Weitz is now at Harvard University, but in the mid-1980s he was working in Exxon’s research and development centre in Annandale, New Jersey – a key international node in the development of soft-matter physics. The Annandale centre hosted some of the first conferences that catalysed the field’s formation, but as Weitz explained, the conference organizers had a problem: nobody knew what to call this new kind of research. After some debate, he recalled, they fell back on the only internationally comprehensible name they could think of: “De Gennes physics”.

That the name of Pierre-Gilles de Gennes should become attached to an entire area of physics indicates his stature as an extraordinary visionary, one who spent his life transforming existing fields, such as superconductivity, and creating brand new ones, such as soft matter. He won the Nobel Prize for Physics in 1991 for his application of methods from condensed-matter physics to liquid crystals and polymers, but he also made his mark by exploring new ways of using theory and interacting with experiment, challenging entrenched institutions and becoming a passionate advocate of education. And of course, he topped it all off with a colourful personal life, in which he fathered two families of children and became a serious amateur artist. Small wonder, then, that an English translation of Laurence Plévert’s biography Pierre-Gilles de Gennes: a Life in Science has been eagerly awaited.

Plévert, a journalist, began interviewing De Gennes in 2005 – two years before the latter’s death. Author and subject worked from notebooks of jottings made by the latter over a 40-year period, and a long list of colleagues, family, collaborators and friends also contributed. The result is a thoroughly researched book. Even one of De Gennes’ closest friends, Phil Pincus of the University of California at Santa Barbara, found that Plévert unearthed episodes they had never spoken about. In Pincus’ case, it was De Gennes’ part in France’s North African nuclear-weapons tests that emerged from obscurity. For me, there was much in the book to fascinate and provide depth to this inspiring character, whom I had known since first meeting him during my PhD in the mid-1980s.

For example, in the first chapter Plévert gives the De Gennes family’s unusual history of French Protestantism an in-depth treatment, suggesting a thought-provoking connection to De Gennes’ later trajectory as someone whose thinking was strongly differentiated from traditional French theoretical physics. Similarly, anecdotes from his postdoctoral period with Charles Kittel in stylish and sunny 1960s Berkeley somehow resonate with his later ease at combining the serious with the flamboyant. I was also unaware of just how closely De Gennes was involved with early neutron-scattering experiments on vortex lattices in type II superconductors. Such close collaboration between theorists and experimentalists gave the French researchers an edge, and characterizes much of the methodology of soft-matter physics today.

After describing De Gennes’ childhood and early career, the book’s narrative tangibly picks up pace when it turns to his time as an assistant professor in Orsay, where his leadership potential first became apparent. De Gennes founded a superconductivity research group there in 1961, only to divert the entire group to the new field of liquid crystals after seven years. Later, at the Collége de France, he did the same with the wider field of soft matter. Plévert keeps this career-related thread ticking along in an accessible manner, weaving between general-audience explanations of techniques such as the renormalization group (one of the methods that De Gennes took from mathematical physics and planted in a new area) and diatribes against his subject’s bêtes noires. These were many and varied, and included conservative traditions in science, the pursuance of long-dead scientific questions, over-formal methods in science education and the editorial prevarications of Nature (after an invited article was rejected, he refused further invitations to write for the journal).

The other thread in the book’s tapestry is De Gennes’ personal relationships, both public and private, and the author treats these in a sensitive and candid way. De Gennes maintained two families, one with his wife Annie and one with his colleague Françoise Brochard-Wyart. The pain this arrangement sometimes caused to those close to him, and the ways in which their resilience permitted it to work, receives the most gracious treatment of the book.

Altogether, A Life in Science is a compelling read, but I came away from it with the impression that its propulsive energy had all come from its subject, rather than its author. Perhaps this is appropriate in a biography, or inevitable in one that attempts to capture greatness. Still, it ought to be possible to make more out of De Gennes’ life than this series of events, anecdotes and aphorisms, however carefully chosen and connected. The author has identified some deep-lying themes, but somehow, they never quite lead to a biography greater than the sum of its parts. Perhaps De Gennes needs a scientific biographer, someone who could be to him what Abraham Pais was to Bohr and Einstein.

The book also contains some annoying technical errors and typos, and this rather lets down an account of De Gennes, who was a scrupulous scientist. For example, the probability that a dropped needle intersects one of a series of parallel lines separated by its own length is 2/π not “2/x”. Such faults are redeemed somewhat by an appendix of technical details, but that, in turn, misses a trick by omitting any references. In addition, the anonymous translator and editor have failed to erase mannerisms that, even if they work in French, most certainly do not in English. My biggest gripe, though, is the book’s frequent use of punctuated dramatic pauses, which work rather…like this! And after a few repetitions, they become…extremely annoying! Well, you get the point.

Still, I urge you to read this book for the force of its central character, and the drama and the delight of discovery that he transmitted throughout his life. Read it, as well, for glimpses of the deep connections in symmetry between phase transitions and polymer molecules, and between superconducting states and milky nematic liquid crystals. But most of all, read it to be reminded that physics is the science that knows no frontiers, and to be taken to some high and wild places by a fearless guide who is missed by all of us who knew him.

BaBar makes first direct measurement of time-reversal violation

The BaBar collaboration has made the first direct observation of time-reversal (T) violation. The results are in agreement with the basic tenets of quantum field theory and reveal differences in the rates at which the quantum states of the B0 meson transform into one another. The researchers say that this measured lack of symmetry is statistically significant and consistent with indirect observations.

The BaBar detector at the PEP-II facility at SLAC in California was designed to study the collisions of electrons and positrons and to determine the differences between matter and antimatter. In particular, physicists working on the experiment are interested in the violation of the charge–parity symmetry (or CP violation). Although the detector was decommissioned in the spring of 2008, data collected during the period of operation continue to be analysed.

Symmetries of the universe

Our current understanding of the universe suggests that it is governed by certain fundamental symmetries. One of these symmetries looks at the relation between charge (C), parity or “handedness” (P), and time (T) – meaning that if you apply a CPT transformation to a system, it shows no difference from the original system. However, physicists are constantly searching for any possible signs of CPT-violation, which could indicate the presence of new physics. In the realm of the weak force, however, instances of the breaking of individual symmetries have been observed in cases of parity inversion or a combination of parity inversion and charge conjugation (CP). Therefore, it was expected that these systems would also show asymmetries when time was reversed. That is, transformation from one state to another would occur at different rates when the process is reversed in time, thus showing a T-violation.

“While CP violation in the B sector is well established by both BaBar and Belle, all CPT-violation tests have always been consistent with zero,” says Patrick Koppenburg, a physicist from the Dutch National Institute for Subatomic Physics (Nikhef), and a member of the LHCb collaboration at CERN. “So, the observation of T violation is not a surprise, but it still needed to be tested.” Indeed, physicists have waited for nearly 50 years to make this direct observation since the discovery of CP violations in 1964. The discovery also comes 14 years after another experiment – the CPLEAR experiment – claimed to have the first experimental proof of the violation in 1998 but this claim proved controversial.

Probing the arrow of time

Electron–positron collisions inside BaBar are tuned to just the right energy for producing Υ(4S) mesons, which are composed of a bottom quark and its antiquark. These Υ particles swiftly decay into B mesons, such as the neutral B0 mesons used in this study.

In 10 years, BaBar detected almost half a billion pairs of B and anti-B mesons. Since these pairs are created from the same Υ, they inherit their quantum numbers from the parent Υ. This “entanglement” of the two simultaneously produced B0 mesons is crucial to observing T violations. “Since the global quantum numbers of the B0-antiB0 system are fixed by the Υ(4S) decay, the state of the first B0 meson to decay – whatever it may be – dictates the state of the other B0 meson at that time, which itself decays after some time into another state,” explains Fernando Martinez-Vidal, who is at the Institute for Particle Physics at the University of Valencia and Spain’s National Research Council (CSIC), and is one of the physicists who worked on this study. “By appropriately choosing the states into which the first and second B0 mesons decay, we can prepare the processes to be studied and compared.”

Forwards and backwards

In the world of quantum physics, the individual mesons can be expressed as superpositions, in terms of linear combinations of both B0 and anti-B0 flavour states. The transformations studied are the change of a B0 meson from a “flavour” state to a “linear-combination” state, and the time-reversed change from a “linear-combination” state to a “flavour” state. To begin with, the BaBar physicists identified the flavour of the first meson in the pair to decay (B0 or anti-B0) and used this information to “tag” the flavour of the second meson. Taking the instant this decay occurred as the starting time, they measured the time it took the second meson to transform into a linear-combination state. They then performed the measurement in reverse: if the first meson transforms into a linear-combination state, this information can be used to determine the linear-combination state of the second meson and measure the time taken for it to decay into a “flavour” state.

Thus, by exchanging the initial and final states of the transformation, the physicists could see if there were any differences in the rates of each of these transformations. Unsurprisingly, they found the difference they were looking for, with a significance of 14σ – in particle-physics experiments, a significance of 5σ and above is considered a definite discovery.

While BaBar may have gone silent nearly half a decade ago, hopefully more new results will emerge from the collected data.

The work is published in Physical Review Letters.

Toshiba sends quantum keys long distances on busy fibres

Quantum information has been transmitted for the first time at a relatively high rate down a long-distance optical fibre that is busy with other telecommunications traffic – something that would normally disrupt quantum communications. The system was developed by researchers at Toshiba’s Cambridge Research Laboratory in the UK together with engineers at Cambridge University. It relies on a detector that can be switched on for about 100 ps (10–10 s) to ensure that it detects a quantum signal efficiently and rejects most of the background noise.

While most quantum-information applications are decades away, some organizations including several banks in Switzerland are already using the technique of “quantum cryptography” to ensure the secrecy of their communications. Quantum key distribution (QKD) allows two parties (by convention called Alice and Bob) to exchange an encryption key, secure in the knowledge that the key – which codes and decodes the data – has not been read by an eavesdropper (called Eve). This guarantee is possible because the key is transmitted in terms of quantum bits (qubits) of information. If intercepted and read by a third party, such qubits are changed irrevocably, which signals to Alice and Bob that Eve has seen the key and so not to use it.

Commercial QKD systems use photons as qubits because the particles can travel long distances in optical fibres without losing their quantum nature. The difficulty, however, is picking out a qubit photon from the noisy background of random photons that are created when much more intense data signals are sent through a commercial telecommunications fibre. One solution that has been adopted is to use “dark fibre”, which does not carry any telecommunications data signal. Unfortunately, leasing or laying dark fibre is very expensive.

Precise timing

What the Toshiba and Cambridge researchers have done is to find a way of filtering out the noise and focussing on the qubit photons. Developed by Zhiliang Yuan and Andrew Shields at Toshiba along with colleagues at Cambridge, the scheme involves Alice creating a qubit photon within a 30 ps time window. The photon is then sent down a 90 km fibre to Bob, who detects the photon by switching on his detector for just 100 ps at the expected arrival time.

Although the fibre is full of noisy photons, most of the randomly arriving noise photons will not reach the detector over this extremely short duration, explains Yuan. As for Bob, he knows exactly when to look for Alice’s photon thanks to a timing system that runs over the same fibre. Based on an off-the-shelf diode laser, the clock signals are sent from Alice to Bob and allow Bob to determine the arrival of the qubit photons to within 10 ps.

The team tested its system on long sections of standard fibres, transmitting standard telecoms data at a rate of 1 Gbit/s in both directions along the fibre, which creates background noise. Despite the noise, the team was able to transmit quantum keys at a rate of 500 kbit/s over a 50 km section of fibre – which is 50,000 times the previous fastest data rate for this distance. The team was also able to send quantum keys at nearly 8 kbit/s over a 90 km fibre – the longest distance yet for an active telecoms fibre.

Perfect for metro networks

Although these distances are not good enough to allow quantum communications across oceans or continents, 90 km is more than enough for a metro network in a large city. Yuan told physicsworld.com that the Cambridge researchers are now working with colleagues in Japan to perform stringent field tests to improve the performance of the system.

As well as QKD, the temporal filtering technology could also find use in other quantum-information applications, where weak quantum signals have to coexist with intense data signals in the same transmission media. One example is distributed quantum-information processing and computing.

The work is described in Physical Review X.

Siemens and Bosch pull out of major African solar initiative

The German firms Siemens and Bosch have announced they are both leaving the Desertec Industrial Initiative (Dii) – a private industry consortium that plans to install a total of 125 GW of solar-power capacity throughout the Middle East and North Africa by 2050. The withdrawal of Siemens and Bosch from Dii, effective at the end of the year, has reignited doubts about the viability of the ambitious hundred-billion-euro project, which would involve piping the energy back to Europe via cables at the bottom of the Mediterranean Sea.

Siemens has also announced it is to completely pull the plug on its solar-energy business. Blaming “changed framework conditions, lower growth and strong price pressure in the solar markets”, the firm will instead focus on developing its wind and hydroelectric power units. Siemens says it is withdrawing from solar because its expectations for solar-energy activities “have not been met”. The firm adds that it sees renewable energy accounting for 28% of global energy use by 2030, but that solar power will make up only 9% of total renewable output, compared with 54% for hydro power and 27% for wind power.

Disappointing, but not fatal

Klaus Schmidtke, a spokesman for Dii, which is based in Munich, acknowledges that the firms’ withdrawal from the project is a disappointment. “Of course, we are not happy about this,” he says. “[But] we do not expect [this decision to have] any negative impact for our initiative.” Schmidtke notes that Siemens was just one of 21 Dii shareholders, and that other companies are still involved in the project (Bosch is only an associate member). These include Swiss industrial firm ABB, electric utility firm E.ON and Deutsche Bank. Schmidke adds that the US solar-panel maker First Solar, currently an associated member of Dii, is in talks to become a full shareholder.

Siemens says that it is already speaking with potential buyers for its photovoltaic activities in its Solar and Hydro Division, adding that the company will continue to produce steam turbines, generators, grid technology, control systems and other items for solar thermal and photovoltaic power plants.

Same old Standard Model

A simulation of an ATLAS event

(Courtesy: CERN)

By Tushna Commissariat

After the rather disappointing news for SUSY researchers from the Hadron Collider Conference in Kyoto this week, it seems as if physicists at the conference have not had anything exciting to say about the Higgs boson either. While both the CMS and ATLAS collaborations did present their latest results, from data collected since the historic Higgs discovery in July, all the current results still point to a Standard Model Higgs.

As a number of other bloggers have already pointed out, what is probably most interesting about these latest results is what is missing – both CMS and ATLAS have only updated certain channels. Conspicuous by its absence was the diphoton (gamma–gamma) channel, which was not updated by either collaboration. The reason for this seems to be some discrepancy between the analysis done by the two experiments, with concerns regarding systematic errors and calibration. Adam Falkowski, who writes the Resonances blog, explains these discrepancies in some more depth.

Papers with the new results from both CMS and ATLAS are available, but the usual blog suspects – Peter Woit, Matt Strassler and the viXra – all agree that the results are anti-climactic. It seems as though we will have to wait until the mysterious diphoton channel gives up its secrets, hopefully by sometime next year, before there is Higgs euphoria again.

Nanotube yarn flexes its muscles

An international team of researchers led by Ray Baughman of the University of Texas at Dallas has developed a new type of artificial muscle made from a “yarn” of twisted carbon-nanotube threads infused with wax. The new actuator structures are different from previously made devices in that they do not need an external electrolyte to function. The muscles can lift more than 100,000 times their own weight, can contract and expand extremely quickly and can operate over a wide temperature range. Such properties could make them ideal for use in a range of future applications, such as humanoid robots, intelligent textiles and advanced rotary motors.

The team made the artificial muscles by first growing a vertically aligned forest of carbon nanotubes. These are hollow cylinders of rolled-up carbon sheets with walls as thin as a single atom. The researchers then drew a thin sheet of nanotube bundles from the forest and twisted this sheet to make a yarn containing helices of intertwined carbon nanotubes. Next, they infused the yarn with molten paraffin wax.

Each end of a thread was then connected to a power supply. When a voltage is applied, the wax heats up and expands. The pressure subsequently produced by this expansion causes the twisted yarn to contract and to partially unwind, which creates a rotating action similar to that seen when stretching a helical spring. The yarn rotates in the opposite direction as the wax cools. Carbon nanotubes are ideal for making such yarns – the sheets are nearly as light as air (they have a density of around just 1.5 mg/cm3) but are stronger than steel, with a specific strength that can reach 560 MPa cm3/g.

Simplified design

Previous artificial-muscle designs work in a similar way but they rely on the nanotubes being immersed in a liquid electrolyte. The use of wax effectively dispenses with the need for such an external conducting liquid, so simplifying the muscle design greatly, explains Baughman.

“The torsional action of the thread can be used to rotate an attached paddle to an average speed of 11,500 revolutions per minute for more than two million reversible cycles,” he says. “The wax-infused nanothreads can also lift more than 100,000 times their own weight and can generate 85 times more mechanical power during contraction than the same size natural muscle. This equates to them being able to lift weights 200 times heavier than is possible for natural muscle of the same diameter.”

Good even without wax

Coiling the nanotube thread increases its thermal expansion coefficient by 10 times, even without the wax filling, he adds. “This thermal expansion is negative, which means that the unfilled yarn contracts as it is heated. Indeed, heating the yarn in an inert atmosphere from room temperature to about 2500 °C (a temperature much higher than the melting point of steel) provides more than 7% contraction when lifting heavy loads – something that has never been seen before for such high-work-capacity actuators.”

According to the researchers, this high thermal expansion for the coiled yarns means that they could be ideal for use in intelligent textiles that would happily function between –50 and 2500 °C. Such proposed textiles would be able to adapt to the needs of the wearer, providing protection in cold conditions, for example, by becoming less porous and cooling the wearer down by becoming more so. Taking this idea a step further might entail incorporating the yarn muscles into sportswear and perhaps even fire-fighter clothing. The artificial muscles might also be used in microfluidic circuits as pumps and for regulating valves, and even in novel applications such as window blinds that open and close in response to ambient temperatures.

“Other possible applications include medial catheters for minimally invasive surgery, nanoactuators and motors in future micromachines, zoom lenses for digital cameras, humanoid robotics, prostheses and exoskeletons,” Baughman says.

Early commercialization possible

Such applications may not just be distant dreams because the researchers have already succeeded in producing kilometre lengths of their yarns. “Since small actuators only require centimetre lengths of thread, this suggests that early commercialization of this material should not be a problem,” says Baughman. “What will be more difficult, however, is to upscale the single-thread actuators to larger ones in which hundreds or thousands of individual muscles operate in parallel.”

The team, which includes scientists from Australia, China, South Korea, Canada and Brazil, is now busy demonstrating new applications for its single-yarn muscles. It is also trying to upscale to large muscles comprising fibre arrays such as those found in natural skeletal muscle.

The current work is detailed in Science.

Should 16–18 year olds be taught modern physics such as quantum mechanics?

By James Dacey

Facebook poll

Earlier this week, my colleague Hamish Johnston wrote this blog entry about a new video that is highly critical of high-school physics education in the US. The video, presented as an open letter to President Barack Obama, bemoans the fact that current curricula in the US focus almost exclusively on classical physics and exclude modern physics such as quantum mechanics almost entirely. The narrator claims that the vast majority of high-school students are not required to learn about any physical phenomena discovered or explained more recently than 1865 (presumably a reference to the year that James Clerk Maxwell published the first version of his famous equations).

The narrator, Henry Reich, is a physicist at the Perimeter Institute for Theoretical Physics in Canada. Reich has released the video on his popular YouTube channel, Minute Physics, in the belief that physics education in the US needs a serious revamp. He argues that the US may lose its standing as the leading nation of innovation unless modern physics concepts such as photons and the structure of atoms are introduced into high-school curricula. He compares the present situation to a scenario in which high-school biology students were not taught about DNA, or geology students were not taught about plate tectonics. For those of you not familiar with the school system in the US, high school refers to students up to 18 years old.

But what do you think about Reich’s sentiments? In theory it would be lovely for all teenagers to be exposed to some of the wonderful ideas of modern physics such as the Higgs boson, antimatter or the cosmological models of how the universe evolved. But the reality is that truly getting to grips with some of these concepts requires an advanced level of maths, which has not always been reached by 18 year olds. The narrator addresses the maths question by saying that great communicators such as Carl Sagan and Neil deGrasse Tyson have triumphed at conveying the fundamental principles of physics in an engaging manner without the need for advanced maths. But, again, the reality is that these people are exceptional – one cannot expect all school teachers to be as gifted at communicating difficult physics as these celebrated TV presenters.

Let us know what you think in this week’s poll.

Should 16–18 year olds be taught modern physics such as quantum mechanics?

Yes, the whole shebang
Yes, but only the ideas not the complex mathematics
No, at this age students should focus on classical principles

To have your say please visit our Facebook page, and please feel free to post a comment to explain your decision.

In last week’s poll we asked another question relating to US politics. We asked you to grade Barack Obama’s governance of US science during his first presidential term? The spread of results was as follows.

A – Awesome 0%
B – Brave effort given the economic constraints 24%
C – Could have done better 44%
D – Dreadful 32%

So in the heads and hearts of our Facebook followers, Obama has his work cut out to meet their expectations in his second term. We hope to hear from you again in this week’s poll. And I’ll make you a promise now that next week’s poll will have nothing to do with US politics!

Millikelvin cooling of large molecules is no myth

In Greek mythology Sisyphus was condemned by the gods to repeatedly push a heavy boulder to the top of a hill, only to see it roll back down to the bottom. Now, physicists in Germany have used a similar scheme to cool a collection of fluoromethane molecules to a temperature of just a few thousandths of a kelvin. Cooling molecules with more than two atoms had proved very difficult and this latest development could lead to breakthroughs in chemistry, particle physics and even quantum computing.

Over the past few decades physicists have developed a variety of tools for cooling gases of atoms ever closer to absolute zero – with temperatures of less than a millionth of a kelvin reached. This has led to all sorts of breakthroughs, such as the creation of an unusual state of matter known as a Bose–Einstein condensate in which all of the constituent particles exist in a single quantum state.

Cooling molecules down to the same temperatures could also lead to major breakthroughs. Potential applications include the development of quantum computers, in which the necessary strong and stable interaction between quantum bits could be achieved via the long-range electrical forces between very low-energy polar molecules. Ultracold molecules might also be used in delicate processes that are impossible to carry out with warmer, more energetic particles, such as using electromagnetic fields to control chemical reactions at the molecular level or observing the tiny difference in energy between left- and right-handed chiral molecules predicted to follow from an inherent asymmetry in the electroweak force.

Unwanted rotations or vibrations

This greater complexity makes molecules much more difficult to cool than atoms using established techniques. One such technique, laser cooling, involves slowing down – and hence lowering the temperature of – atoms in a gas by making them absorb photons from laser beams pointed in opposing directions. About 10,000 such interactions are needed to cool each particle in the gas and any one interaction could cause unwanted rotation or vibration of a molecule.

Despite these difficulties, in 2010 researchers in the US managed to cool down a gas of diatomic (two-atom) molecules using lasers. And this year another American group achieved a similar result using evaporative cooling, which lowers the temperature of a gas by allowing the most energetic particles to escape. But this latest work by Gerhard Rempe and colleagues at the Max Planck Institute for Quantum Optics outside Munich published in Nature extends cooling to molecules made up of five atoms.

The team used a gas of fluoromethane, its molecules consisting of three atoms of hydrogen, one of carbon and one of fluorine. Rather than rely on the puny kicks of individual photons to slow down the particles in a gas, Rempe’s group instead uses the much greater energy available in an external electric field. The researchers’ “electric trap” consists of two parallel capacitor plates, each 4 cm by 2 cm and separated by a gap of 3 mm. The inside surfaces of the plates are patterned to create an electric field that is uniform in the centre of the gap but that grows stronger closer to the plates.

Climbing the well

Initially, pre-cooled molecules are held in the centre of the trap thanks to the potential well set up by their interaction with the electric field. After being excited to a vibrational state by an infrared laser fired through the trap, the molecules spontaneously decay to an intermediate-energy rotational state chosen so that it creates a deeper potential well than that in the molecules’ initial, lower-energy state. The molecules then figuratively “climb up” the sides of this well, losing kinetic energy as they do so, and are subsequently hit by a beam of microwaves that forces them back down to the edge of the shallower well beneath. As they fall back down the sides of this well, the molecules pick up less kinetic energy than they forego in the intermediate state. This means that, on balance, they lose energy. The idea is that by repeating this process several times the molecules can be cooled to extremely low temperatures.

In fact, the researchers were able to reduce the temperature of about one million fluoromethane molecules by more than a factor of 10, to about 30 mK, in only around a dozen cycles. In a commentary piece accompanying the paper, John Barry and David DeMille of Yale University say that this small number of cycles was crucial, since it allowed the molecules to be cooled even though about 10% of the sample was lost in each cycle because of unwanted rotational or vibrational excitations.

Other researchers contacted by physicsworld.com were also positive. Rudi Grimm of Innsbruck University in Austria says that physicists are “desperately lacking” efficient ways of cooling molecules and that the “proof-of-principle demonstration” carried out by the German group “looks very good”. Wolfgang Ketterle of the Massachusetts Institute of Technology, meanwhile, says he is “impressed” by the latest work, arguing that it and “other recent progress” on molecular cooling “opens the door to ultracold chemistry”.

Breaking the 1 mK barrier

Zeppenfeld says that his group’s next step is to try and get below 1 mK, at which point, he believes, the molecules could be used for applications such as quantum computing. Achieving this, he says, might involve making detection of the cooled molecules more efficient or employing molecules that decay in less time than the roughly 0.1 s typical of fluoromethane, in order to limit unwanted collisions with background gas in the trap.

The cooling scheme is described in Nature.

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