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Nearly seeing Hawking radiation?

Astrophysicists have known for more than three decades that black holes shouldn’t be totally black — they should emit a certain amount of “Hawking radiation” from the production of particle–antiparticle pairs around their event horizons. But detecting Hawking radiation has so far proved tricky, mostly because its temperature would be at least eight orders of magnitude lower than the cosmic microwave background left over from the Big Bang.

One way round this problem, as Ulf Leonhardt and colleagues from the University of St Andrews, UK, demonstrated earlier this year, might be to create systems that are analogous to black holes in the lab in which the temperature of the radiation is much higher. The researchers showed that a pulse of light travelling through a fibre can behave like a black hole, and, although they didn’t actually detect Hawking radiation, they showed that in principle it should be possible.

Now, in a paper published today in the New Journal of Physics, is seems as though Leonhardt’s group are one step closer. Rather than use pulses of light as an analogous system to a black hole, they have built a system of water waves. I confess that I haven’t yet studied this paper carefully enough to describe with any certainty what the researchers have done, suffice it to say they claim to have observed “negative-frequency” waves, the classical analogue of anti-particles which are the hallmarks of Hawking radiation.

In a brief email conversation last week, Leonhardt told me that they are not yet sure whether this is enough to constitute an observation of a classical analogue of Hawking radiation: “Hawking’s effect is a quantum phenomenon, a spontaneous quantum process, but like all spontaneous processes it can be stimulated. This is what we did, we sent in waves and saw a tiny bit of stimulated negative-frequency waves, but there are quantitative differences between experiment and theory that we do not understand yet.”

Of course, if and when Leonhardt’s group do find negative-frequency waves that agree with theory, there will be a debate as to whether they are “real” Hawking radiation. No doubt you will be seeing more of this on physicsworld.com soon.

Quantized conductance seen in graphene

Quantized conductance — whereby the current through a wire changes in a stepwise, rather than continuous manner — has been seen in very narrow ribbons of graphene for the first time. The discovery was made by physicists in the US, who claim that this first sighting is an important step towards using such graphene “nanoribbons” in transistors that are much smaller than those used in electronics devices today.

Graphene — which is a 2D sheet of carbon just one atom thick — could have great potential as a material for making tiny electronic devices because it is both a semiconductor and a very good electrical conductor. At just one atom thick, it is about as small as you can get, and unlike many other tiny structures, graphene is relatively easy to work with.

However, graphene is a “zero-gap” semiconductor, meaning that there is no energy gap between its conduction and valence electron-energy levels — and it is such a gap that allows conventional semiconductors such as silicon to be used to make transistors and other electronic devices.

Confined to 1D

One way of creating energy gaps in a material is to make it into an extremely thin wire so that its electrons are effectively confined to move in only one dimension. This creates a series of electron energy levels separated by gaps. If the voltage along such a wire is increased, the current will increase in a stepwise manner because each energy level can accommodate a small fixed number of electrons.

Although such quantized conductance has already been measured in tiny semiconductor nanowires and carbon nanotubes, it had yet to be seen in graphene nanoribbons.

Now, Yu-Ming Lin and colleagues at IBM’s TJ Watson Research Center in New York have seen the effect in graphene nanoribbons (arXiv:0805.0035). The researchers made their nanodevices from single-layer graphene sheets that were placed on a silica/silicon substrate. Nanoribbons as narrow as 30 nm were created by electron beam lithography — a technique that is used in the semiconductor industry. The electrical properties of the nanodevices were then measured at various temperatures.

This phenomenon will allow researchers to achieve various quantum effects in graphene for fundamental research and for technological applicationsYu-Ming Lin, IBM

“The fact that conductance quantization can be observed in our narrow ribbon devices at temperatures as high as 80 K indicates that they have uniform width along the transport channels, and that the channels are of excellent quality,” said Lin. “This phenomenon will allow researchers to achieve various quantum effects in graphene for fundamental research and for technological applications,” Lin told physicsworld.com. “For example, the quantized conductance behaviour in graphene may lead to multi-valued logic operations beyond the conventional binary ones, and may also be used to make 1D electron ‘quantum waveguides’.”

The team will now try to understand the impact of edge disorders on the quantized conductance behaviour of the devices. The scientists also plan to fabricate ultra-narrow channels to achieve quantized conductance at room temperature — something that would be essential for practical devices.

Einstein's mistakes

albert.jpg

“Many of [Einstein’s] ground-breaking discoveries were blighted by mistakes, ranging from serious misconceptions in physics to blatant errors in mathematics”.

So says a promotional blurb for Einstein’s Mistakes: The Human Failings of a Genius, a new book from the American physicist and author Hans C Ohanian that will be published in September by W W Norton.

Ohanian has posted an eight-page taster of his work on the arXiv preprint server, in which he presents a “critical examination” of how Einstein went about proving his most famous equation E = MC2. All of these proofs, claims Ohanian, “suffer from mistakes”.

This is not the first time that Einstein’s proofs have come under scrutiny, with various detractors and supporters arguing since at least 1908 — three years after the equation was first derived.

Elsewhere in the world of Einstein biography, a letter on religion written in 1954 by the physicist to the German philosopher Eric Gutkind has come up for auction in London. “The word God is for me nothing more than the expression and product of human weakness…”, wrote Einstein who died the next year — and has presumably discovered whether or not this letter was a mistake.

Neil Turok chosen to lead Perimeter Institute

The cosmologist Neil Turok will be the next executive director of Canada’s Perimeter Institute for Theoretical Physics, taking over in October. Turok, who is currently Chair of Mathematical Physics at the University of Cambridge in the UK, described the move as the “opportunity of a lifetime” and told physicsworld.com that he plans to make the institute “the leading centre in the world for theoretical physics”.

The Perimeter Institute (PI) was founded in 1999 by Mike Lazaridis, chief executive of Research in Motion — the company that makes Blackberry wireless handheld devices. Located in Waterloo, Ontario, and home to more than 60 resident researchers, the institute focuses on fundamental questions in areas such as cosmology, particle physics and quantum gravity. Its first executive director Howard Burton, left suddenly in June 2007 and the Canadian theoretical physicist Robert Myers has been acting as interim director while the institute looked for a new head.

More international perspective

Turok told physicsworld.com that one of his goals will be to give the institute a more “international perspective” by attracting “ the most brilliant students and researchers from around the world”.

He will work with local universities to expand the institute’s graduate teaching, making it “the best graduate programme in fundamental theoretical physics”. Turok also has plans for a “pre-PhD programme”, which would invite undergraduate students from all over the world and expose them to how theoretical physics is done. “Often undergraduates are not prepared for doing research, they are mostly prepared for passing exams”, he said.

Turok is looking forward to the intellectual freedom that the institute offers. “What Mike [Lazaridis] has done is to bring a breath of fresh air into theoretical physics”, he said.

Importance of basic science

Lazaridis himself told physicsworld.com: “The more I got to know Dr Turok, the more conviction I had that he was the right person to take Perimeter to the next level”. “We share deep convictions in the importance of basic science, the importance of funding basic science, and the importance of philanthropy in promoting basic science for the advancement of mankind”, he added.

Born in South Africa in 1958, Turok founded the African Institute for Mathematical Sciences in Cape Town, which supports the development of mathematics and science research and education across Africa. In addition to his work on the polarization of the cosmic microwave background, Turok has also developed a cyclic model of the universe with Paul Steinhardt at Princeton University.

Turok’s colleague at Cambridge, Stephen Hawking, said of his appointment: “The combination of Neil and PI is brilliant and holds great promise for the future”.

The return of the 'Science Warrior'

Plugging his new book last night in Bristol — the UK city where Physics World is based — was physicist Alan Sokal. The New York University professor rose to fame in 1996 when he published his famous hoax paper Transgressing the Boundaries: Towards a Transformative Hermeunetics of Quantum Gravity in the cultural-studies journal Social Text.

Sokal had written the paper, which was filled with scientific-sounding gibberish, to highlight what he saw as the sloppy thinking of some sociologists of science, particularly those who deem scientific knowledge to be socially constructed, rather than a matter of objective truth.

His paper sparked what became known as the Science Wars, which saw furious debate in scholarly journals and magazines, including Physics World, between physicists and sociologists. Now Sokal is back on the scene with his new book Beyond the Hoax, published by Oxford University Press.

Speaking at Bristol’s Festival of Ideas, Sokal outlined the main themes of Beyond the Hoax. Post-modernist views as espoused by some sociologists still get his goat, but now that some in that camp have, as he puts it, back-tracked from their earlier, more radical stance, Sokal has extended his criticisms to other groups who he thinks also don’t embrace the rational, empirical thinking that is the hallmark of all science.

That basically boils down to four main groups: religious people, pseudoscientists, proponents of homoepathic medicine, and spindoctors and others involved in PR. He saved particular anger for George Bush and Tony Blair for deciding to go to war with Iraq and then retrospectively justifying the decision based on what Sokal saw as weak evidence such as dodgy satellite photos.

Overall, it’s a bigger pool of victims for Sokal’s ire. But by broadening the range of targets, my concern is that his initial fury from 10 years ago has got somewhat diluted.

To his credit, Sokal responded well to the grilling given by his audience, although the majority were, I’d guess, generally supportive of his main themes. A fuller version of his lecture was previously given in London earlier this year. Meanwhile, Physics World has commissioned a review of Beyond the Hoax, to be published later this summer — so keep an eye out online and in print for an authoritative assessment of his new tome.

Nobel laureates petition Bush over funding shortfall

A group of 20 Nobel-prize-winning physicists have written to US President George Bush, asking him to work with Congress to find at least $510m in “emergency supplemental funding” for the agencies that pay for much of the nation’s physics research. The laureates sent the letter in response to a similarly-sized shortfall in the amount of money granted by Congress for scientific research in this financial year compared with what Bush had first proposed.

Instead of providing incentives for budding scientists, the funding plan provides discouragement

“[The 2008 budget] sends a terrible message to the next generation of scientists,” the laureates complain in their letter. “Instead of providing incentives for budding scientists, the funding plan provides discouragement”. The letter’s signatories include laser pioneer Charles Townes, particle theorist Frank Wilczek and 2006 winners, the cosmologists George Smoot and John Mather.

The funding situation in the US been difficult this year because the budget for the 2008 fiscal year — which began in October 2007 — was only agreed upon in December 2007, after 11 months of wrangling between the President and Congress. This delay was bad news for those researchers and institutes that had already started spending their 2008 money, only to find that their funding had been cut back or even curtailed.

Two fields financed by the Department of Energy have been particularly badly hit, with funding for high-energy physics falling to $688m — some 12% less than Bush had requested — and support for fusion falling by a third. The cuts led to Fermilab, for example, announcing plans earlier this year to lay-off 200 of the lab’s 1900 staff.

Permanent damage

In the letter, the laureates complain that “hundreds of scientists have been laid off; research grants have been slashed; and facilities operations have been seriously curtailed at national laboratories”, as a result of the shortfall. They also warn that the damage done to American science in 2008 “will become permanent if it is not rectified within the next few months”. This damage, they say, could hamper the nation’s ability to respond to “increased global competition from countries such as China, India, and South Korea”.

Wolfgang Ketterle, who shared the 2001 prize for his work on Bose-Einstein condensates, told physicsworld.com why he signed the letter: “I know from my own experience that scientific progress needs continuity and predictability of funding, both for current research efforts, and for attracting new talent”. He added “the current budget situations does not reflect this”.

The budget cuts have also caused US physicists to limit severely their participation this year in several international projects — including the International Thermonuclear Reactor (ITER), which is being built in France, and the International Linear Collider. “[The 2008 budget] is damaging our reputation as a reliable partner for international projects,” the laureates complain.

Respite in 2009

Bush has already submitted a funding request for 2009, which — if approved — would provide some respite for researchers as it includes significant increases in science spending. In particular, the extra money could allow the US to resume full contributions to ITER and the ILC. In their letter, the laureates “applaud” Bush’s commitment to science but warn that the 2008 funding problems require immediate action. “We strongly urge you to work with Congress in the coming weeks to enact emergency supplemental funding”.

The $510m comprises $310m for the Department of Energy’s Office of Science, $170m for the National Science Foundation and $30m for the National Institute of Standards and Technology.

Kei Koizumi, a budget analyst at the American Association for the Advancement of Science, told physicsworld.com “There is a chance, but a shrinking chance, that 2008 physics funding could be added by Congress this week”. However he cautioned “it’s increasingly likely that everyone will have to wait until 2009 for more physical sciences funding”.

Polar vortex replicated in a bucket

If you were in a spacecraft passing over the Earth’s South Pole, you are likely to see a “polar vortex” — a huge swirling mass of clouds and winds in the upper atmosphere right above the pole, driven by the Earth’s rotation. The centre of the vortex is usually circular, but occasionally it assumes a triangular or even a square shape. Now researchers in Canada claim to have replicated this behaviour for the first time in the laboratory — using nothing more than water in a cylindrical bucket with a rotating base.

While it might seem strange that a circular vortex will suddenly develop corners, this curious behaviour was first hinted at over a century ago by the British physicist J J Thomson. Working on the now long-abandoned theory of “vortex atoms”, which assumed that each atom is a vortex in the ether, Thomson calculated that when a single vortex reaches a critical angular velocity, it will split into two vortices that orbit each other, making a diatomic molecule.

As the angular velocity increased further, Thomson predicted that the system would separate into three, four, five and six vortices, creating larger molecules. This idea of multiple vortices was largely forgotten until 1979, when Richard Packard and colleagues at the University of California, Berkeley saw as many as 11 vortices in a rotating cylinder of superfluid helium (Phys Rev Lett 43 214).

Some physicists believe that the curious polygonal shapes of the polar vortex could be formed when multiple “satellite vortices” coexist with a central vortex. For example three satellite vortices and a central vortex would combine to make a triangular shape. Now, Georgios Vatistas and colleagues at Concordia University may have observed this effect for the first time in the laboratory (Phys Rev Lett 100 174503 ).

Give it a whirl

Vatistas’s team studied water vortices in a stationary cylindrical bucket with a rotating disk at its bottom. As the disk spins, it causes a whirlpool to form in the bucket. The centrifugal effect causes the water to climb the wall of the bucket, leaving a depression in the centre. If the disk is spun fast enough, the depression reaches right to the bottom of the bucket and the centre of the disk has no water on it.

The researchers used a digital camera to take one photo of the dry region per revolution using a synchronized stroboscope. Initially, the dry region of the disk was circular — but as the angular velocity of the disk increased, the dry region split into two lobes, followed by a triangle, square, pentagon and hexagon. Despite further increases in angular velocity, the team saw no evidence of polygons with seven or more sides.

Vatistas told physicsworld.com that while more experimental and theoretical work is needed to understand why the polygons are being formed, he believes that they are probably created by the coexistence of a central vortex with specific configurations of satellite vortices.

“We are still observing and mapping the phenomenon in detail”, said Vatistas. Then, armed with more detailed experimental data, the team plan to use the mathematical theory of vortex formation along with numerical simulations to gain a deeper understanding of why the polygons are formed.

Saturn and beyond

Vatistas believes that the work could lead to a better understanding of the dynamics of Earth’s atmosphere. Polygonal structures have also been seen in the “eyes” at the centre of some hurricanes, for example. Beyond Earth, a hexagonal structure has been spotted at Saturn’s north pole and triangular shapes have been spotted at the centre of the spiral galaxy NGC 598 — leading some astrophysicists to suggest that its core contains three satellite vortices.

Reflecting on this latest contribution to the study of vortices, Packard at Berkeley told physicsworld.com “I do find it fascinating that vortices, which occur in so many places in nature, are still the object of research after over two hundred years of scrutiny by some of the best minds in science”.

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.

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