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superluminal light
Scientists in PML’s Quantum Measurement Division have produced the first superluminal light pulses made by using a technique called four-wave mixing, creating two separate pulses whose peaks propagate faster than the speed of light in a vacuum.
Laser Cooling and Trapping Group researcher Paul Lett and colleagues report in a forthcoming paper in Physical Review Letters that this new method of generating “fast light” has resulted in a pulse that travels up to 50 ns faster over the length of a 1.7-cm cell than it would if it were moving through a vacuum.
The findings could have a significant impact on optical communications systems in which signal quality may be improved by speeding up or slowing down pulses. In addition, investigation of the quantum-mechanical correlations between the seed and conjugate pulses will provide fundamental insights into quantum coherence, with potential implications for future quantum information-processing.(via First, fast, and faster)
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April 2nd1 note
F O R E V E R
This tiny ball provides evidence that the universe will expand forever.
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Lightning? Neutrons? Whaa?
For the last 30 years there has been a very small controversy rumbling in the hallowed halls of physics. Way back in 1985, scientists from the then-USSR noted that whenever a thunder storm passed over their neutron detector, they observed an increased flux of neutrons. Unfortunately, they didn’t have much in the way of monitoring equipment to really nail down much beyond the initial observation.
Since then, scientists have put forward a couple of potential explanations for the observed flux. One was that the high fields generated during lightning strikes was modifying the trajectories of muons from cosmic ray showers. In short: these are cosmic rays, and this is not interesting. The second was that the gamma rays emitted during the lightning strike generated neutrons, a photonuclear event. But new measurements show that neither of these explanations can explain the data.
The (now) Russian scientists have designed an entirely new experiment that significantly improves their previous results. They installed three neutron detectors that were sensitive to low energy neutrons: one above ground, one partially shielded in a building, and a third underground with heavier shielding. Sitting next to the underground detector was a more traditional neutron detector that is sensitive to high energy neutrons. Finally, the electrical activity of incoming storms was monitored using a variety of instruments, allowing for better correlation between the neutron measurements and the electrical activity of any passing storms.
Why the variety of neutron detectors? Essentially, the researchers need to get rid of the background noise from cosmic rays. The cosmic rays generate muons that collide with something in or very near the detector, resulting in neutrons that have the high energy of the muon being registered. Neutrons from lightning, on the other hand, can only have the energy given up by a fission event, which is then lost in collisions with molecules in the air as they travel to the detector.
from Lightning strikes produce free neutrons, and we’re not sure how
*Bonus round*: I CAN HAZ BALL LIGHTNING?
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Inflation, the brief period that occurred less than a second after the Big Bang, is nearly as difficult to fathom as the Big Bang itself. Physicists calculate that inflation lasted for just a tiny fraction of a second, yet during this time the Universe grew in size by a factor of 10^78. Also during this time, a very important thing occurred: fluctuations in the quantum vacuum appeared, which later resulted in the temperature fluctuations in the cosmic microwave background (CMB) that in turn produced large-scale structures such as galaxies. But in a new study, physicists now think that their understanding of the features of primordial quantum fluctuations – also called the inflationary power spectrum – may require a few small corrections due to currently unknown physics. These new corrections could allow scientists to search for experimental evidence to test a variety of quantum gravity theories, including string theory.
Theoretical physicists Mark G. Jackson of the University of Paris-7 Diderot in Paris, France, and Koenraad Schalm of the University of Leiden in Leiden, The Netherlands, have published their study on these possible signatures of new physics in the inflationary power spectrum in a recent issue of Physical Review Letters.
Primordial fluctuations
The physicists’ work focuses on the Planck scale, the ultra-high-energy conditions at the time of the Big Bang. Although the universe at this point was almost completely homogeneous, the violent dynamics of inflation produced tiny inhomogeneities from the quantum vacuum. Virtual pairs of particles from the quantum vacuum began popping in and out of existence, some of which could absorb energy and become real. Physicists think that all matter today, from galaxies to living things, originated from these primordial quantum fluctuations. But physicists are even more interested in this era for what it may reveal about quantum gravity.
“The Planck scale is the energy at which the two major theories in physics – gravity and quantum field theory – necessarily combine,” Jackson and Schalm told PhysOrg.com. “The resultant theory of quantum gravity is one of the major open problems in physics, though by now there is a lot of evidence that string theory is the answer. In an ideal world one would wish to test this experimentally. Unfortunately, this Planck energy scale is laughably beyond the reach of standard experiments such as particle accelerators: it would be like reaching out your hand to touch the Moon. Fortunately, Nature did once perform an ultra-high-energy experiment possibly capable of probing the Planck scale: the Big Bang. Now while we can’t re-do the Big Bang, we can witness its consequences.”(via Physicists search for new physics in primordial quantum fluctuations)
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Crystals may be possible in time as well as space
What sounds like the title of a bad fantasy movie — time crystals — could be the next big thing in theoretical physics.
In two new papers, Nobel Prize–winning physicist Frank Wilczek lays out the mathematics of how an object moving in its lowest energy state could experience a sort of structure in time. Such a “time crystal” would be the temporal equivalent of an everyday crystal, in which atoms occupy positions that repeat periodically in space.
The work, done partly with physicist Alfred Shapere of the University of Kentucky, appeared February 12 on arXiv.org.
“We don’t know whether such things do exist in nature, but the surprise is that they can exist,” says Maulik Parikh, a physicist at Arizona State University in Tempe.
Scientists don’t know how important time crystals may turn out to be, or whether they have any practical application at all. But Wilczek, of MIT, says the concept reminds him of the excitement he felt when he helped describe a new class of fundamental particles, called anyons, in the early 1980s. “I had very much the same kind of feeling as I’m having here,” he says, “that I had found a new logical possibility for how matter might behave that opened up a new world with many possible directions.” -
ANU scientists have successfully bent light beams around an object on a two dimensional metal surface, opening the door to faster and cheaper computer chips working with light.
The international team, including three members from the Research School of Physics and Engineering at ANU, have successfully demonstrated that a tiny beam of light on a flat surface can be bent around an obstacle, and course-correct itself on the other side of that obstacle. It’s the world’s first two-dimensional demonstration of so-called ‘Airy beams’. Their paper on the subject will be published in this month’s Physical Review Letters.
“Students in science class learn that light rays travel along straight trajectories and that it can’t go around corners,” said ANU team member Professor Yuri Kivshar.
“Recently it was discovered that small beams of light can be bent in a laboratory setting, diffracting much less than a regular beam. These rays of light are called ‘Airy Beams,’ and named after the English astronomer Sir George Biddell Airy, who studied light in rainbows.
“Our team has demonstrated that these beams can also be bound on the flat surface of a chip. We also observed a fascinating property of these beams – the so-called self-healing phenomenon, where the wave recovers after passing through surface defects,” he said.
Fellow ANU team member Dr Dragomir Neshev says that this demonstration offers potential in a number of areas.
“This discovery offers some exciting possible applications, particularly in the area of communications technology where it could allow us a cheap way to manipulate light on a chip,” he said. -
As a quantum theory of gravity, loop quantum gravity could potentially solve one of the biggest problems in physics: reconciling general relativity and quantum mechanics. But like all tentative theories of quantum gravity, loop quantum gravity has never been experimentally tested. Now in a new study, scientists have found that, when black holes evaporate, the radiation they emit could potentially reveal “footprints” of loop quantum gravity, distinct from the usual Hawking radiation that black holes are expected to emit.
In this way, evaporating black holes could enable the first ever experimental test for any theory of quantum gravity. However, the proposed test would not be easy, since scientists have not yet been able to detect any kind of radiation from an evaporating black hole.
The scientists, from institutions in France and the US, have published their study called “Probing Loop Quantum Gravity with Evaporating Black Holes” in a recent issue of Physical Review Letters.
“For decades, Planck-scale physics has been thought to be untestable,” coauthor Aurélien Barrau of the French National Institute of Nuclear and Particle Physics (IN2P3) told PhysOrg.com. “Nowadays, it seems that it might enter the realm of experimental physics! This is very exciting, especially in the appealing framework of loop quantum gravity.”
In their study, the scientists have used algorithms to show that primordial black holes are expected to reveal two distinct loop quantum gravity signatures, while larger black holes are expected to reveal one distinct signature. These signatures refer to features in the black hole’s energy spectrum, such as broad peaks at certain energy levels.
Using Monte Carlo simulations, the scientists estimated the circumstances under which they could discriminate the predicted signatures of loop quantum gravity and those of the Hawking radiation that black holes are expected to emit with or without loop quantum gravity. They found that a discrimination is possible as long as there are enough black holes or a relatively small error on the energy reconstruction.
While the scientists have shown that an analysis of black hole evaporation could possibly serve as a probe for loop quantum gravity, they note that one of the biggest challenges will be simply detecting evaporating black holes.
“We should be honest: this detection will be difficult,” Barrau said. “But it is far from being impossible.”
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Oh, yeah. Moving faster than the speed of light has been the hot topic in the news and OPERA has been the key player. In case you didn’t know, the experiment unleashed some particles at CERN, close to Geneva. It wasn’t the production that caused the buzz, it was the revelation they arrived at the Gran Sasso Laboratory in Italy around 60 nanoseconds sooner than they should have. Sooner than the speed of light allows!
Since the announcement, the physics world has been on fire, producing more than 80 papers – each with their own opinion. While some tried to explain the effect, others discredited it. The overpowering concensus was the OPERA team simply must have forgotten one critical element. On October 14, 2011, Ronald van Elburg at the University of Groningen in the Netherlands put forth his own statement – one that provides a persuasive point that he may have found the error in the calculations.
To get a clearer picture, the distance the neutrinos traveled is straightforward. They began in CERN and were measured via global positioning systems. However, the Gran Sasso Laboratory is located beneath the Earth under a kilometre-high mountain. Regardless, the OPERA team took this into account and provided an accurate distance measurement of 730 km to within tolerances of 20 cm. The neutrino flight time is then measured by using clocks at the opposing ends, with the team knowing exactly when the particles left and when they landed.
But were the clocks perfectly synchronized?
Keeping time is again the domain of the GPS satellites which each broadcasting a highly accurate time signal from orbit some 20,000km overhead. But is it possible the team overlooked the amount of time it took for the satellite signals to return to Earth? In his statement, van Elburg says there is one effect that the OPERA team seems to have overlooked: the relativistic motion of the GPS clocks.
(via Special relativity may answer faster-than-light neutrino mystery)
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A well-known method of making heat sinks for electronic devices is a process called sintering, in which powdered metal is formed into a desired shape and then heated in a vacuum to bind the particles together. But in a recent experiment, some students tried sintering copper particles in air and got a big surprise.
Instead of the expected solid metal shape, what they found was a mass of particles that had grown long whiskers of oxidized copper. “It was sort of serendipitous,” says Kripa Varanasi, d’Arbeloff Assistant Professor of Mechanical Engineering at MIT. “We got this crazy stuff, particles covered in nanowires,” he says.
The resulting process could turn out to be an important new method for manufacturing structures that span a range of sizes down to a few nanometers (billionths of a meter) in size. “You go in one step from solid spherical powder to very complex structures,” says Christopher Love, a mechanical engineering graduate student who is lead author on the paper. “The process is very simple, and the structures are durable,” he says. These new structures could be used for managing the flow of heat in various applications ranging from powerplants to the cooling of electronics.
Not only were the particles covered with fine wires, but the abundance of the wires turned out to be dependent on the size of the original copper particles. “We are the first to observe a size-dependent oxidation in copper,” Varanasi says. That means researchers can easily synthesize porous structures at various scales, in bulk, by selecting the particles they start out with: Particles smaller than a certain size sinter, while larger particles grow nanowires.
The discovery is reported in a paper being published in the journal RSC Nanoscale. In addition to Varanasi and Love, the paper’s authors are mechanical engineering graduate student J. David Smith and postdoc Yuehua Cui of the Laboratory for Manufacturing and Productivity.
Such hierarchical structures can be very effective for thermal management, cooling everything from microprocessors to the boilers of huge powerplants. They might even prove useful in engineered geothermal power, which holds great promise as a system for providing clean, renewable power. Because the resulting structures are so easily controlled, “you can optimize them to control phenomena taking place at different length and time scales,” Varanasi says.
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'Light-speed' neutrinos point to new physical reality
[This New Scientist article is only available to subscribers so it has been presented in its entirety.]
SUBATOMIC particles have broken the universe’s fundamental speed limit, or so it was reported last week. The speed of light is the ultimate limit on travel in the universe, and the basis for Einstein’s special theory of relativity, so if the finding stands up to scrutiny, does it spell the end for physics as we know it? The reality is less simplistic and far more interesting.
“People were saying this means Einstein is wrong,” says physicist Heinrich Päs of the Technical University of Dortmund in Germany. “But that’s not really correct.”
Instead, the result could be the first evidence for a reality built out of extra dimensions. Future historians of science may regard it not as the moment we abandoned Einstein and broke physics, but rather as the point at which our view of space vastly expanded, from three dimensions to four, or more.
“This may be a physics revolution,” says Thomas Weiler at Vanderbilt University in Nashville, Tennessee, who has devised theories built on extra dimensions. “The famous words ‘paradigm shift’ are used too often and tritely, but they might be relevant.”
The subatomic particles - neutrinos - seem to have zipped faster than light from CERN, near Geneva, Switzerland, to the OPERA detector at the Gran Sasso lab near L’Aquila, Italy. It’s a conceptually simple result: neutrinos making the 730-kilometre journey arrived 60 nanoseconds earlier than they would have if they were travelling at light speed. And it relies on three seemingly simple measurements, says Dario Autiero of the Institute of Nuclear Physics in Lyon, France, a member of the OPERA collaboration: the distance between the labs, the time the neutrinos left CERN, and the time they arrived at Gran Sasso.
But actually measuring those times and distances to the accuracy needed to detect nanosecond differences is no easy task. The OPERA collaboration spent three years chasing down every source of error they could imagine (see illustration) before Autiero made the result public in a seminar at CERN on 23 September.
Physicists grilled Autiero for an hour after his talk to ensure the team had considered details like the curvature of the Earth, the tidal effects of the moon and the general relativistic effects of having two clocks at different heights (gravity slows time so a clock closer to Earth’s surface runs a tiny bit slower).
They were impressed. “I want to congratulate you on this extremely beautiful experiment,” said Nobel laureate Samuel Ting of the Massachusetts Institute of Technology after Autiero’s talk. “The experiment is very carefully done, and the systematic error carefully checked.”
Most physicists still expect some sort of experimental error to crop up and explain the anomaly, mainly because it contravenes the incredibly successful law of special relativity which holds that the speed of light is a constant that no object can exceed. The theory also leads to the famous equation E = mc2.
Hotly anticipated are results from other neutrino detectors, including T2K in Japan and MINOS at Fermilab in Illinois, which will run similar experiments and confirm the results or rule them out (see “Fermilab stops hunting Higgs, starts neutrino quest”).
In 2007, the MINOS experiment searched for faster-than-light neutrinos but didn’t see anything statistically significant. The team plans to reanalyse its data and upgrade the detector’s stopwatch. “These are the kind of things that we have to follow through, and make sure that our prejudices don’t get in the way of discovering something truly fantastic,” says Stephen Parke of Fermilab.
In the meantime, suggests Sandip Pakvasa of the University of Hawaii, let’s suppose the OPERA result is real. If the experiment is tested and replicated and the only explanation is faster-than-light neutrinos, is E = mc2 done for?
Not necessarily. In 2006, Pakvasa, Päs and Weiler came up with a model that allows certain particles to break the cosmic speed limit while leaving special relativity intact. “One can, if not rescue Einstein, at least leave him valid,” Weiler says.
The trick is to send neutrinos on a shortcut through a fourth, thus-far-unobserved dimension of space, reducing the distance they have to travel. Then the neutrinos wouldn’t have to outstrip light to reach their destination in the observed time.
In such a universe, the particles and forces we are familiar with are anchored to a four-dimensional membrane, or “brane”, with three dimensions of space and one of time. Crucially, the brane floats in a higher dimensional space-time called the bulk, which we are normally completely oblivious to.
The fantastic success of special relativity up to now, plus other cosmological observations, have led physicists to think that the brane might be flat, like a sheet of paper. Quantum fluctuations could make it ripple and roll like the surface of the ocean, Weiler says. Then, if neutrinos can break free of the brane, they might get from one point on it to another by dashing through the bulk, like a flying fish taking a shortcut between the waves (see illustration).
This model is attractive because it offers a way out of one of the biggest theoretical problems posed by the OPERA result: busting the apparent speed limit set by neutrinos detected pouring from a supernova in 1987.
As stars explode in a supernova, most of their energy streams out as neutrinos. These particles hardly ever interact with matter. That means they should escape the star almost immediately, while photons of light will take about 3 hours. In 1987, trillions of neutrinos arrived at Earth 3 hours before the dying star’s light caught up. If the neutrinos were travelling as fast as those going from CERN to OPERA, they should have arrived in 1982.
OPERA’s neutrinos were about 1000 times as energetic as the supernova’s neutrinos, though. And Pakvasa and colleagues’ model calls for neutrinos with a specific energy that makes them prefer tunnelling through the bulk to travelling along the brane. If that energy is around 20 gigaelectronvolts - and the team don’t yet know that it is - “then you expect large effects in the OPERA region, and small effects at the supernova energies,” Pakvasa says. He and Päs are meeting next week to work out the details.
The flying fish shortcut isn’t available to all particles. In the language of string theory, a mathematical model some physicists hope will lead to a comprehensive “theory of everything”, most particles are represented by tiny vibrating strings whose ends are permanently stuck to the brane. One of the only exceptions is the theoretical “sterile neutrino”, represented by a closed loop of string. These are also the only type of neutrino thought capable of escaping the brane.
Neutrinos are known to switch back and forth between their three observed types (electron, muon and tau neutrinos), and OPERA was originally designed to detect these shifts. In Pakvasa’s model, the muon neutrinos produced at CERN could have transformed to sterile neutrinos mid-flight, made a short hop through the bulk, and then switched back to muon before reappearing on the brane.
So if OPERA’s results hold up, they could provide support for the existence of sterile neutrinos, extra dimensions and perhaps string theory. Such theories could also explain why gravity is so weak compared with the other fundamental forces. The theoretical particles that mediate gravity, known as gravitons, may also be closed loops of string that leak off into the bulk. “If, in the end, nobody sees anything wrong and other people reproduce OPERA’s results, then I think it’s evidence for string theory, in that string theory is what makes extra dimensions credible in the first place,” Weiler says.
Meanwhile, alternative theories are likely to abound. Weiler expects papers to appear in a matter of days or weeks.
Even if relativity is pushed aside, Einstein has worked so well for so long that he will never really go away. At worst, relativity will turn out to work for most of the universe but not all, just as Newton’s mechanics work until things get extremely large or small. “The fact that Einstein has worked for 106 years means he’ll always be there, either as the right answer or a low-energy effective theory,” Weiler says.
(via New Scientist)
Related reading » Neutrinos: Everything you need to know
(via section5)
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Can You See Me Now? New X-Ray System Reveals Fine Detail
X-rays can help reveal anything from bombs hidden in luggage to tumors in breasts, but some potentially vital clues might be too faint to capture with conventional methods. Now a new x-ray technique adapted from atom smashers could resolve more key details.
Conventional x-ray imaging works much like traditional photography, relying on the light—in this case, x-rays—that a target absorbs, transmits and scatters. To make out fine details, one typically needs a lot of x-rays, either over time, which can expose targets to damaging levels of radiation, or all at once from powerful sources such as circular particle accelerators, or synchrotrons, which are expensive.
Instead physicist Alessandro Olivo of University College London and his colleagues suggest imaging an object by looking for very small deviations in an x-ray’s direction as it moves through that object. Their idea is to take such x-ray phase-contrast imaging, which has been used in synchrotrons for more than 15 years, and use it with conventional x-rays.
(via Scientific American)
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New nanostructured glass for imaging and recording
University of Southampton researchers have developed new nano-structured glass, turning it into new type of computer memory, which has applications in optical manipulation and will significantly reduce the cost of medical imaging.
In a paper entitled Radially polarized optical vortex converter created by femtosecond laser nanostructuring of glass published in Applied Physics Letters, a team led by Professor Peter Kazansky at the University’s Optoelectronics Research Centre, describe how they have used nano-structures to develop new monolithic glass space-variant polarisation converters. These millimetre-sized devices change the way light travels through glass, generating ‘whirlpools’ of light that can then be read in much the same way as data in optical fibres. This enables more precise laser material processing, optical manipulation of atom-sized objects, ultra-high resolution imaging and potentially, table-top particle accelerators. Information can be written, wiped and rewritten into the molecular structure of the glass using a laser.
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Physicists Weigh Antimatter with Amazing Accuracy
A new measurement provides the most accurate weight yet of antimatter, revealing the mass of the antiproton (the proton’s antiparticle) down to one part in a billion, researchers announced today (July 28).
To give a sense of just how accurate their measurement was, researcher Masaki Hori said: “Imagine measuring the weight of the Eiffel Tower. The accuracy we’ve achieved here is roughly equivalent to making that measurement to within less than the weight of a sparrow perched on top. Next time it will be a feather.”
The result, detailed this week in the journal Nature, may help scientists investigate the mystery of why the universe is made of regular matter even though they suspect roughly equal parts of matter and antimatter were around just after the universe formed. When a particle, such as a proton, meets with its antimatter partner, the antiproton, the two annihilate each other in a powerful explosion.
(via LiveScience)
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The electromagnetic force has gotten a little stronger, gravity a little weaker, and the size of the smallest “quantum” of energy is now known a little better. The National Institute of Standards and Technology (NIST) has posted the latest internationally recommended values of the fundamental constants of nature.
The constants, which range from relatively famous (the speed of light) to the fairly obscure (Wien frequency displacement law constant) are adjusted every four years in response to the latest scientific measurements and advances. These latest values arrive on the verge of a worldwide vote this fall on a plan to redefine the most basic units in the International System of Units (SI), such as the kilogramand ampere, exclusively in terms of the fundamental constants.
The values are determined by the Committee on Data for Science and Technology (CODATA) Task Group on Fundamental Constants, an international group that includes NIST members. The adjusted values reflect some significant scientific developments over the last four years.
(via The constants they are a changin’: NIST posts latest adjustments to fundamental figures)
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Beyond the Inclined Plane: Websites that explain and apply physics.
What is science?, What can be done with science?, Why study physics?… Websites that illustrate physics. Internet teaching tools and classroom examples of everyday physics from biology, geology, homes, and factories. Links to video clips, applets, and animations that help teach physics in the classroom.
In short, an excellent resource center. Do not miss it.
