Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist

Quantum split: Particle this way, properties that way - physics-math - 23 July 2014 - New Scientist: In Grenoble, the Vienna team used a feeble magnetic field and a weakly interacting neutron absorber to make the weak measurements. They found that when they put the absorber in one path of the interferometer (say left), there was a discernible effect at the output. But when they put it in the right path, it had no such effect. The neutrons were travelling in one path only.

Next, the experimenters introduced a weak magnetic field near each arm of the interferometer, to interact with the spin of the neutrons. When they did this in the left path, there was no change in the interferometer's output. If they introduced the magnetic field in the right path, though, there was a change: the magnetic field had interacted with the spin. In other words, they had confirmed that the spin had chosen the path not taken by the parent neutron...

White holes: Hunting the other side of a black hole - space - 20 July 2014 - New Scientist

White holes: Hunting the other side of a black hole - space - 20 July 2014 - New Scientist: Perhaps the fact that we have found no signs of a white hole, despite peering ever deeper into space, is a more fundamental problem. Enter a space telescope called RadioAstron whose wildly elongated orbit takes it out to a distance of 350,000 kilometres – nearly as far as the moon and 30 times wider than Earth's diameter. Launched from Kazakhstan's Baikonur Cosmodrome in 2011, its dish is only 10 metres across. But when its signals are combined with those from radio telescopes on Earth, the resulting images are as sharp as those from a dish 350,000 kilometres wide...

"...once we spot a gigantic powerful gamma-ray burst with a lot of radio radiation, we will take a close look with RadioAstron and try to determine its shape and size for the first time." That could provide important clues about its source. "It may be a white hole or a wormhole. Maybe the flashes are coming from another universe."

Quantum bounce could make black holes explode : Nature News & Comment

Quantum bounce could make black holes explode : Nature News & Comment: The theory suggests that the transition from black hole to white hole would take place right after the initial formation of the black hole, but because gravity dilates time, outside observers would see the black hole lasting billions or trillions of years or more, depending on its size. If the authors are correct, tiny black holes that formed during the very early history of the Universe would now be ready to pop off like firecrackers and might be detected as high-energy cosmic rays or other radiation. In fact, they say, their work could imply that some of the dramatic flares commonly considered to be supernova explosions could in fact be the dying throes of tiny black holes that formed shortly after the Big Bang.

Is time moving forward or backward? Computers learn to spot the difference | Science/AAAS | News

Is time moving forward or backward? Computers learn to spot the difference | Science/AAAS | News: To find out, she and her collaborators broke down 180 YouTube videos into square patches of a few hundred pixels, which they further divided into four-by-four grids. Combining standard techniques for discovering objects in still photographs with motion detection algorithms, the researchers identified 4000 typical patterns of motion, or “flow words,” across a grid’s 16 cells. The gentle downward drifting of snowflakes, for example, would be one flow word. From those patterns, the team created flow word descriptions of each video along with three other versions—a time-reversed version, a mirror-image version, and a mirror-image and time-reversed version. Then, they made a computer program watch 120 of these clips, training it to identify which flow words best revealed whether a video ran forward or backward.

When they tested their program on the remaining 60 videos, the trained computers could correctly determine whether a video ran forward or backward 80% of the time...  A closer analysis found that flow words associated with divergence (water splashing outward as someone dives into a pool) or dissipation (a steam train’s exhaust spreading out in air) were especially good indicators of the direction in which time was moving.

A new topological insulator breaks symmetry, and that's a good thing

A new topological insulator breaks symmetry, and that's a good thing: Most topological insulators operate as either a p-type or n-type material on both top and bottom surfaces. But BiTeCl is asymmetric: p-type on its top surface and n-type on its bottom. This means the edges of the material could function as p-n junctions – or even many microscopic p-n junctions layered on top of each other. Even better, when the material is placed in a magnetic field, these p-n junctions develop unique edge channels that can conduct electricity with zero resistance, Chen said – and this opens all sorts of possibilities.

Moreover, this unique type of material can demonstrate many other phenomena. For instance, placing it in a static electric field can induce useful magnetic properties in the material, a phenomenon known as the topological magneto-electric effect, first predicted by theorist Shoucheng Zhang of the Stanford Institute for Materials and Energy Sciences and his group. You could even use an electric charge to induce magnetic monopoles – theorized magnets that have just one pole, north or south, rather than the usual two – and then use this exotic magnetic state to do practical work, such as storing information on a hard drive, Chen said. "This is very bizarre," he said, "because people have never found magnetic monopoles as fundamental particles."

Soft-Drink Cans Focus Sound Waves to a Point, Beating Diffraction Limit: Scientific American

Soft-Drink Cans Focus Sound Waves to a Point, Beating Diffraction Limit: Scientific American: The group generated audible sound from a ring of computer speakers surrounding the acoustic 'lens': a seven-by-seven array of empty soft-drink cans. Because air is free to move inside and around the cans, they oscillate together like joined-up organ pipes, generating a cacophony of resonance patterns. Crucially, many of the resonances emanate from the can openings, which are much smaller than the wavelength of the sound wave, and so have a similar nature to evanescent waves.

To focus the sound, the trick is to capture these waves at any point on the array. For this, Lerosey and his team used a method known as time reversal: they recorded the sound above any one can in the resonating array, and then played the recording backwards through the speakers...

Normal waves scatter efficiently, so they disappear quickly. However, the evanescent-like waves are less efficient at scattering, and take roughly a second to make it out of the can--a prolonged emission that allows the build up of a narrow, focused spot...

Penn State Live - Search for advanced materials aided by discovery of hidden symmetries

Penn State Live - Search for advanced materials aided by discovery of hidden symmetries: Before the publication of this paper, scientists and engineers had five different types of symmetries to use as tools for understanding the structures of materials whose building blocks are arranged in fairly regular patterns. Four types of symmetries had been known for thousands of years -- called rotation, inversion, rotation inversion and translation -- and a fifth type -- called time reversal -- have been discovered about 60 years ago. Now, researchers at Penn State University have added a new, sixth, type, called rotation reversal. As a result, the number of known ways in which the components of such crystalline materials can be combined in symmetrical ways has multiplied from no more than 1,651 before to more than 17,800 now...
The "eureka moment" of the discovery occurred when Gopalan recognized that the simple concept of reversing the direction of a spiral-shaped structure from clockwise to counterclockwise opens the door to a distinctly new type of symmetry. Just as a square shape has the quality of rotation symmetry even when it is not being rotated, Gopalan realized that a spiral shape has the quality of rotation-reversal symmetry even when it is not being physically forced to rotate in the reverse direction. Their further work with this rotation-reversal concept revealed many more structural symmetries than previously had been recognized in materials containing various types of directionally oriented structures. Many important biological molecules, for example, are said to be either "right handed" or "left handed," including DNA, sugars, and proteins.

Introducing the Anti-laser, Absorbing Beams of Light - NYTimes.com

Introducing the Anti-laser, Absorbing Beams of Light - NYTimes.com: The incoming beam is split in two, and hits the medium from two sides. The photons bounce around between the mirrors and interfere with one another, eventually wiping themselves out in a flurry of electrons and heat.

The experimental device absorbed about 99.4 percent of the light. In theory, an anti-laser should be able to absorb 100 percent.

Ultrasound beam lets scientists see deep into human tissue | KurzweilAI

Ultrasound beam lets scientists see deep into human tissue | KurzweilAI: Wang’s guide star is an ultrasound beam that “tags” light that passes through it. When it emerges from the tissue, the tagged light, together with a reference beam, creates a hologram.

When a “reading beam” is then shown back through the hologram, it acts as a time-reversal mirror, creating light waves that follow their own paths backward through the tissue, coming to a focus at their virtual source, the spot where the ultrasound is focused.

The Fantastical Promise of Reversible Computing� - Technology Review

The Fantastical Promise of Reversible Computing� - Technology Review: "But there are a number of computing schemes that have the potential to work like this. Thapliyal and Ranganathan point in particular to the emerging technology of quantum cellular automata and show how their approach might be applied.

The beauty of this approach is that it has the potential to be dissipation-free. So not only would it use far less energy than conventional computing, it needn't lose any energy at all. At least in theory."

Eternal black holes are the ultimate cosmic safes - space - 03 September 2010 - New Scientist

Eternal black holes are the ultimate cosmic safes: Hsu realised that running the process backwards would be equivalent to a black hole forming and then existing in a perfect vacuum, with no Hawking radiation. "It becomes a black hole that's not radiating, which is a very weird thing," Hsu says.

The snag is that to run this process backwards and make the eternal black hole, you would need to send in a precisely crafted burst of radiation as the hole forms. The radiation would have to be "exactly tuned to interfere with the Hawking radiation that would otherwise come out", says Hsu.

Technology Review: Blogs: arXiv blog: Why Space Isn't Filled with White Holes

Technology Review: Blogs: arXiv blog: Why Space Isn't Filled with White Holes: "White holes are closely linked with black holes, being their time-reversed equivalent. The thinking is that whatever black holes can do, white holes also do in reverse.

That leads to an odd conclusion. In the 1970s, Stephen Hawking showed that in certain circumstances black and white holes become identical. When they are in thermal equilibrium with their surroundings, he said, they ought to absorb and emit the same amount of radiation and therefore be indistinguishable."