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Home » Page 1647

Weiler to remain NASA science chief

NASA boss Michael Griffin has announced that Edward Weiler will remain the agency’s chief executive of science after almost six weeks as an interim replacement.

Weiler stepped in as science chief on 26 March when Alan Stern, who had occupied the post for a little over a year, resigned following a disagreement with Griffin over budget cuts to the Mars Exploration Rover (MER) mission. In a statement issued yesterday, Griffin said that he is pleased Weiler decided to accept the position on a permanent basis. “His leadership style and 26 years of headquarters experience will be vital to the success of upcoming science activities and missions,” he added.

Since 2004 Weiler has been director of NASA’s Goddard Space Flight Centre, and prior to that he was associate administrator for the agency’s Space Science Enterprise. In the past he has also been director of NASA’s Astronomical Search for Origins Programme and between 1979 and 1998 was chief scientist for the Hubble Space Telescope.

Scientists at NASA will be eager to see how Weiler fares managing project overruns amid the US government’s tight-fisted approach to science budgets. The agency’s budget for 2008 remained flat at $4.7bn, and for 2009 the Bush Administration requested that it drop by $265m. Stern refused to cut budgets from healthy projects and instead opted to make cuts to popular programmes such as the MER’s Spirit and Opportunity rovers — a move that was overturned by Griffin and which ultimately led Stern to quit.

From an interview last month on the website Space News, Weiler implied he also would not be a pushover. “If programs get out of control and I suspect they weren’t going to be able to get back within control, I have a clear record as the associate administrator for six years,” he said. “I cancelled five programs. I’m capable of doing that again. On the other hand I’m also going to make sure that programs aren’t nickel-and-dimed just to save a few cents, because I have direct personal experience where cost was the only concern.”

Atom laser makes its first measurement

Physicists in Australia have for the first time performed a measurement task with an atom laser. The achievement opens up the possibility of manipulating an atom-laser beam so that it may be used to process quantum information.

An atom laser is made from a Bose–Einstein condensate, a collection of ultracold atoms that have all fallen into the same quantum state. BECs generally have to be trapped — for example, with magnetic fields — but if some of the atoms are allowed to escape the confining potential they can produce a travelling matter wave.

Just like the light from a conventional laser, the matter wave from an atom laser is coherent and therefore has a well-defined quantum field that can be manipulated for processing and transmitting quantum information or for making measurements. Indeed, because atoms have a greater momentum than photons from conventional lasers they have a smaller de Broglie wavelength, which in principle means an atom laser can make spatial measurements that are more precise.

“In my opinion the experiment we have done really shows an important new direction that we are following,” John Close of the Australian National University in Canberra told physicsworld.com. “We and several other groups have spent many years developing the atom laser to be a useful tool.”

Two condensates

The measurement performed by Close and colleagues was of the interaction between an atom laser and another BEC, both made of rubidium–87 atoms but in different “hyperfine” states. The researchers positioned the atom laser above the second BEC so that its matter wave would fall through the lower collection of atoms and scatter. Then, by shining light at right angles to the plane of motion and recording the absorption distribution, they measured the scattering length — that is, how close scattering atoms got to each other — to be 94 times the radius of the atom’s electron cloud (arXiv:0805.0477).

“All other measurements that we know of in the field of atom lasers have been used to characterize the properties of the atom-laser beam itself rather than to use an atom laser to make a measurement of another quantity,” says Close.

Although the measurement of scattering length itself for those hyperfine states is not new, the fact that Close and colleagues have performed it with an atom laser is important because it will help physicists to understand how to manipulate atom lasers so they can be used in quantum information systems. This can already be achieved with conventional lasers by sending the light through non-linear media, leading, for example, to entangled photon beams.

Wolfgang Ketterle, a condensed-matter physicist at the Massachusetts Institute of Technology, US, who invented the atom laser in 1997, says that, although the Australian group’s experiment has not produced any new results or realized new concepts, it is imaginative and “uses a few nice tricks.”

Close explains that it is still “very early days” for applying atom lasers to measurement. “We have plans to produce high flux, tuneable, continuous and squeezed atom lasers that we think will be applicable to precision measurement in a variety of fields from surface science to metrology.”

Who cares if it’s not even wrong?

“So what would you do if string theory is wrong?” asks string theorist Moataz Emam of Clark University, US, in a paper posted on arXiv yesterday. It’s obvious, you might think. String theorists would briefly mourn the 40 years of misspent speculation and leave furtively through the back door, while anti-string theorists would celebrate in light of their vindication.

Not so, says Emam — string theory will continue to prosper, and might even become its own discipline independent of physics and mathematics.

Oddly, the reason Emam gives for this prediction is precisely the same reason why many physicists despise string theory. For example, in reducing the 10 dimensions of string theory to our familiar four, string theorists have to fashion a “landscape” of at least 10500 solutions. Emam says that such a huge number of solutions — of which only one exists for our universe — may make string theory unattractive, but in studying them physicists are gaining “deep insights into how a physical theory generally works”:

So even if someone shows that the universe cannot be based on string theory, I suspect that people will continue to work on it…The theory would be studied by physicists and mathematicians who might no longer consider themselves either. They will continue to derive beautiful mathematical formulas and feed them to the mathematicians next door. They also might, every once in a while, point out interesting and important properties concerning the nature of a physical theory which might guide the physicists exploring the actual theory of everything over in the next building.

Peter Woit, author of the string-theory polemic Not Even Wrong, notes on his blog that physicists looking to pursue string theory for its beauty should “go and work in a maths department”:

The argument Emam is making reflects in somewhat extreme form a prevalent opinion among string theorists, that the failure of hopes for the theory, even if real, is not something that requires them to change what they are doing. This attitude is all too likely to lead to disaster.

Is this the youngest professor ever?

Sabur.jpg

According to the Guinness Book of World Records, and what appears to be most major media outlets, Alia Sabur (pictured above) has broken the record for the world’s youngest professor.

Sabur, 19, will begin teaching physics next month at the Department of Advanced Technology Fusion at Konkuk University, Korea. It will be just another entry on the teenager’s laden CV, which reveals she received a bachelor’s degree at 14 and a masters in materials science at 17.

Something might be awry here, though. There’s nothing wrong with the media adopting the American English definition of “professor” (i.e. any university teacher) — after all, Sabur was born in New York. But it appears that the previous record holder was Scottish physicist Colin Maclaurin, who was appointed professor of mathematics at the University of Aberdeen when he was a few months over 19 in 1717.

I might have to explain to our international readers that in the UK “professor” is a more distinguished title, reserved for heads-of-departments and the like. (At least it has been as far back as any of us at Physics World can vouch for.) Sabur, I note, is yet to defend her PhD.

Does this mean the titles of Sabur and Maclaurin are being confused? Does Maclaurin, who is credited with the mathematical “Maclaurin series”, deserve to keep his accolade?

Of course, science was a considerably narrower discipline back in the 18th century, and achieving a professorship might have taken a little less time than it does today (it certainly wouldn’t have required a PhD). But Maclaurin can’t defend his honour, and offhand I don’t know enough about science in the early 1700s to cast a vote either way.

Do any of you have any thoughts? Feel free to comment below.

Prospect of US science debate wanes

Organizers of ScienceDebate 2008 are “disappointed” but “not surprised” that the three main US presidential candidates have ignored invitations to participate in a public debate on science that was scheduled to take place today.

Friday 2 May was one of three possible dates this month that had been put forward to the candidates after the original date — 18 April — had to be cancelled, also because of a poor response.

John McCain, the likely Republican nominee, declined the invitation for a debate at any time in early May. Hillary Clinton, one of the two remaining Democratic candidates, told the organizers that the invitation had gone to her “scheduling” department, while Barack Obama, the other Democratic candidate, acknowledged receipt of the invitation but did not confirm whether he would attend.

“I believe the candidates have left it so late that it is now virtually impossible that the debate will happen,” Matthew Chapman, president of ScienceDebate, told physicsworld.com. “For the candidates to show such disdain of the academic, science and technology community should be a matter of concern for every voter in [the US].”

Although McCain is the only candidate to have formally rejected the two remaining dates — 9 May and 16 May — it seems unlikely that either Clinton or Obama will accept at this late stage. The organizers are now pinning their hopes on new invitations that will be sent out shortly. “We are making progress in bringing this to the attention of voters, and if everyone continues to keep the pressure up, ultimately the candidates will have to respond,” says Chapman.

Growing support

ScienceDebate 2008 was formed towards the end of last year by a group of six people who wanted science policy to be debated by the presidential candidates in the run up to the November election. Since then the organizers have gathered the signatures of some 37,000 supporters including university presidents, the representatives of scientific institutions and Nobel laureates.

McCain has no reason to appear on stage with the Democrats, and the focus of the Democratic debates has devolved into issues of personality and gossip Lawrence Krauss, co-organizer, ScienceDebate 2008

After the original date in April was rejected, several signatories — including the Nobel laureates David Gross, John Mather, David Politzer and Leon Lederman — sent an independent letter urging the candidates to respond to the new May invitations. But this too appears to have gone unheeded.

Lawrence Krauss, co-organizer of Science Debate, says that resounding “gossip and innuendo” between the Clinton and Obama campaigns is to blame for the lack of interest in a serious public debate on science. “At this point McCain has no real reason to appear on stage with the Democrats, and the focus of the Democratic debates has devolved into issues of personality and gossip.”

Krauss now believes it is more likely that the debate will happen after the primaries are over in June. “I am only hoping that after the primary season ends that real issues may come to the fore, but this will depend in part on the media actually focusing in on these issues,” he says, adding: “We are in this for the long haul, and are hoping to set up an infrastructure that will impact not just upon this election but future elections.”

How lasers really work

Researchers in Switzerland and the US have developed a new theoretical framework for describing a wide range of lasers — including unconventional systems called diffusive random lasers, which had hitherto defied a complete explanation. Their theory could open the door for unconventional lasers to be used in a wider range of commercial applications such as document security, remote sensing, ultra-fast displays and diagnostic imaging.

A conventional laser comprises an optical gain medium, such as a gas, that is sandwiched between two mirrors in an optical cavity. The gain medium is “pumped” using an external source of light or electric field such that most of its atoms or molecules are in higher energy excited states.

When these states decay, they emit light that bounces back and forth in the cavity. This feedback stimulates the emission of similar light from other atoms in excited states. The result is a cavity filled with unidirectional light at the same wavelength, some of which is allowed to escape to form a laser beam.

Random multiple scattering

The random laser — which does not have an optical cavity — was born in the mid-1990s, when Nabil Lawandy of Brown University in the US fired a laser beam at a beaker filled with dye that is normally used as a gain medium in a conventional laser. Lawandy found that when tiny particles of metal were added to the beaker, the dye began to lase. The laser is random in the sense that the feedback for the photons generated in the dye is provided by the random multiple scattering of light from the particles.

But exactly why this was happening was a mystery — particularly because the addition of scattering particles to a conventional dye laser was known to reduce its performance. As physicists began making random lasers utilizing different lasing media they discovered that there were actually two different kinds of random lasers.

One is the localized random laser, in which light is believed to be confined to “hot-spots” (a situation closer to that of a conventional cavity laser). The other is the diffusive random laser, or DRL, in which the particles are not very reflective. In a DRL the light effectively seeps out of the medium rapidly, instead of being confined. This rapid escape of light is very different than what occurs in an optical cavity, leaving physicists wondering how a DRL could function as a laser.

Researchers have had some success describing a theory of localized random lasers, but an understanding of DRLs had been difficult to pin down. But now, Hakan Türeci of the Swiss Federal Institute of Technology in Zurich and Douglas Stone and Colleagues at Yale University have come up with a new general theory of lasers that explains the operation of both types of random laser as well as more conventional lasers (Science) .

Extreme leakiness

The team used their theory to create computer simulations that can model the extreme leakiness of a DRL and determine a number of key parameters of the laser including its output power and the wavelengths of the laser light emitted. Inputs to the simulation include the distribution of scattering particles in the medium and the pumping power.

Their model considers all possible ways that light can reflect back and forth in the medium (its resonant modes) and works out how these modes interact with each other to define the wavelengths of the light that is produced by the laser.

Using the simulation, the team was able to reproduce a key feature of DRLs that had eluded previous theories – that the wavelengths of the laser light emitted are always the same, no matter how the DRL is pumped.

The team is currently using their theory to understand the stability of the output wavelengths. Türeci is also confident that the theory will be used to boost the performance of other unconventional lasers such as those based on chaotic resonators or photonic crystal-based cavities.

Random lasers have already been used by Nabil Lawandy to create a document security system whereby a liquid containing reflective particles is “painted” onto a piece of paper. When the material dries, it can be made to emit laser light by firing a laser at it. The precise wavelengths of the light emitted are defined by the exact locations of all the reflective particles in the dried paint — something that is different for each daub. The result is a unique signature that cannot be reproduced.

“Pine tree” nanowires do the Eshelby twist

Frost, icicles and snowflakes are all too familiar to the people of Wisconsin, especially on winter mornings. But the icy-looking structures in the image above, created by scientists at the University of Wisconsin–Madison, US, didn’t form in the cold — they are nanowire “pine trees” grown via chemical vapour deposition (CVD) of lead sulfide at temperatures verging on 650 °C.

CVD is often used to grow nanowires, but it usually requires a catalytic nanoparticle “seed” to get the structure started. Song Jin and colleagues have found that by modifying the flow of hydrogen gas used in CVD the nanowires do not need a catalytic seed. Instead, the growth of their nanowires can be driven by a type of defect known as a screw dislocation, which creates a spiral step for atoms to settle on. When the researchers follow-up the CVD with another deposition technique, known as vapour-liquid-solid growth, horizontal nanowires grow outwards from the steps to form tree-like structures (Science doi: 10.1126/science.1157131).

Although Jin’s team have created branched nanowires before, this is the first time they have created structures with such intricacy. In fact, they think their nanowire pine trees are so intricate they might be the best evidence yet for a theory of dislocations called the Eshelby twist. This theory, put forward by 55 years ago by materials scientist John Eshelby, then at the University of Illinois at Urbana, proposes that the stress created by a dislocation generates a torque at either end of the cylinder, forcing it to twist.

Eshelby twists have been observed in nature before, but the horizontal branches in nanowire pine trees could serve as markers to highlight the extent of it. Jin’s team think Eshelby’s theory will help them to understand the layout of the branches of their nanowire pine trees, in doing so providing the “clearest demonstration” of the theory’s validity. “Lying beneath these beautiful nanostructures is a beautiful and fundamental science that goes back to the heart of crystal growth theory,” says Jin.

Nickel-based compound joins a new class of superconductor

The high Tc superconductivity community has been abuzz lately with the discovery of a growing number of iron-based materials that remain superconducting at temperatures as high as 55 K.

The first such material (fluorine-doped LaOFeAs) was reported by physicists in Japan earlier this year and has a transition temperature (Tc) of 26 K. Since then, researchers in China replaced the lanthanum (La) with samarium (Sm) and boosted Tc to 55 K. The Japanese team, meanwhile, put their material under pressure and increased Tc to 43 K.

Now, just as physicists are beginning to understand the mechanism behind these iron-based materials, scientists in Russia have come up with a new twist by replacing iron with nickel. They found that fluorine-doped LaONiBi is a superconductor with a Tc of 4K.

While this Tc is much lower than the iron-based materials, the team reports that LaONiBi has very similar structural and electronic properties as its iron-based cousins. This suggests that with a bit of fiddling with doping levels and other properties, the Tc could be boosted considerably.

Blog Life: Star Stryder

Who is the blog written by?

Pamela Gay is an astronomer at the Southern Illinois University in the US. As well as carrying out research, Gay is also keenly involved in science outreach. She puts together the Internet radio show Astronomy Cast, which consists of weekly 30-minute broadcasts each exploring a different topic in astronomy.

What topics does the blog cover?

According to Gay herself, Star Stryder is a blog focused on astronomy, academia and the scientific method, with some content related to teaching, the boundary between science and religion, and life as an astronomer thrown in for good measure. In practice, this means lots of astronomy results are explained and dissected, while we also get an idea of what daily life is like for the author. And, of course, like most bloggers she can’t resist drawing attention to interesting science stories in the media such as this quote from a National Geographic article: “CERN’s scientists, the fine people who brought us the W and Z particles, anti-hydrogen atoms and hyperlinked porn web pages, are now hard at work building the Large Hadron Collider to discover something even cooler: the Force. Yes, that Force. Or like physicists call it, the Higgs boson.”

Who is it aimed at?

Unlike most other blogs written by scientists, Star Stryder is aimed squarely at the interested general public. Gay takes her outreach role seriously, and is always careful to explain the science at an appropriate level for this audience.

Why should I read it?

As this blog is in large part an outreach project, it combines first-hand insight into scientific results and how science is done with the clarity and level of explanation more usually associated with journalists’ blogs. Together with Gay’s approachable and humorous writing style, this makes Star Stryder rare in the blogosphere.

How often is it updated?

Usually about once a day, with each post stretching to a few hundred words. When Gay is at an event, however, such as the recent Lunar and Planetary Society Conference, she tries to report on all the interesting talks and people she meets, which results in several posts a day. When you remember that she is also putting together material for Astronomy Cast, this really is an impressive feat.

Can you give me a sample quote?

As you probably know, my name is Pamela Gay. This is the name I was born with (yes, middle school was hell). I could have taken my husband’s last name when I got married a couple years ago, but at 32 I didn’t feel like changing, and I quite honestly can’t pronounce my husband’s very French, fairly long, last name properly. (Really. I say it and anyone who can speak French giggles rather violently.) So, Pamela Gay it is. This can be problematic. Our lab manager didn’t get any of my emails for the first several months I was here because my last name was considered sexually explicit content that needed blocking by his spam filter. Now, a good colleague in the UK (and possibly a second colleague) has been unable to receive my emails on his university accounts for ˜6 months. I tried 6 different email accounts the other day and none of my emails got through.

Embargoed science

Physicists love to complain about the way in which science is covered by the mainstream media. News stories, they say, are either inaccurate, overhyped or dominated by dinosaurs, medical research and errant asteroids that might collide with the Earth. Many will therefore be delighted to learn that BBC Radio 4 in the UK is planning to devote a whole day of programmes on an as-yet-unspecified date in July to particle physics, when CERN injects beams into the Large Hadron Collider for the first time.

But science is rarely afforded such blanket coverage and mostly has to make do with news stories about individual research articles. Many of these stories are based on papers in Nature and Science, which use a system of “embargoes” whereby thousands of journalists are e-mailed details of upcoming articles in advance on the proviso that they do not report on them before a certain time. When the embargo lifts, the journal in question often receives prominent and widespread coverage of those papers (see “Mind the hack”).

Some commentators have called for the system to be abandoned because it encourages “pack journalism”, whereby reporters feel pressurized to cover particular papers for fear of being scooped by rival publications. The system also encourages science to be reported as a series of neat breakthroughs when in fact it usually takes a much messier path. Moreover, embargoes give undue prominence to papers in a small number of journals and can put off science journalists from carrying out more in-depth investigations.

However, embargoes do serve science by allowing journalists the time to write accurate stories on tricky subjects, and axing the system could lead to a decline in the number of science stories in the mainstream media. After all, very few journalists currently look for stories in journals like Physical Review Letters, which does not embargo any of its papers. The bigger problem for science reporting is a lack of resources — BBC News has just six science reporters — and an over-reliance by all journalists (not just those who cover science) on press releases: a trend that has been dubbed “churnalism”. Embargoes have their faults, but it is doubtful whether abandoning them would do much good for science communication.

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