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      The Universe in a lab: Testing alternate cosmology using a cloud of atoms / ArsTechnica · Friday, 1 December - 20:04 · 1 minute

    Multicolored waves spread out within a pill-shaped area.

    Enlarge / Density waves in a Bose-Einstein condensate. (credit: NASA )

    In the basement of Kirchhoff-Institut für Physik in Germany, researchers have been simulating the Universe as it might have existed shortly after the Big Bang. They have created a tabletop quantum field simulation that involves using magnets and lasers to control a sample of potassium-39 atoms that is held close to absolute zero. They then use equations to translate the results at this small scale to explore possible features of the early Universe.

    The work done so far shows that it’s possible to simulate a Universe with a different curvature. In a positively curved universe, if you travel in any direction in a straight line, you will come back to where you started. In a negatively curved universe, space is bent in a saddle shape. The Universe is currently flat or nearly flat, according to Marius Sparn, a PhD student at Kirchhoff-Institut für Physik. But at the beginning of its existence, it might have been more positively or negatively curved.

    Around the curve

    “If you have a sphere that's really huge, like the Earth or something, if you see only a small part of it, you don't know—is it closed or is it infinitely open?” said Sabine Hossenfelder, member of the Munich Center for Mathematical Philosophy. “It becomes a philosophical question, really. The only things we know come from the part of the Universe we observe. Normally, the way that people phrase it is that, for all we know, the curvature in this part of the Universe is compatible with zero.”

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      The Ars guide to time travel in the movies / ArsTechnica · Friday, 24 November - 12:30 · 1 minute

    The selected films span several decades to show how Hollywood's treatment of time travel in Hollywood has evolved.

    Enlarge / The selected films span several decades to show how Hollywood's treatment of time travel in Hollywood has evolved. (credit: Aurich Lawson | Getty Images)

    Since antiquity, humans have envisioned various means of time travel into the future or the past. The concept has since become a staple of modern science fiction. In particular, the number of films that make use of time travel has increased significantly over the decades, while the real-world science has evolved right alongside them, moving from simple Newtonian mechanics and general relativity to quantum mechanics and the notion of a multiverse or more exotic alternatives like string theory.

    But not all time-travel movies are created equal. Some make for fantastic entertainment but the time travel makes no scientific or logical sense, while others might err in the opposite direction, sacrificing good storytelling in the interests of technical accuracy. What we really need is a handy guide to help us navigate this increasingly crowded field to ensure we get the best of both worlds, so to speak. The Ars Guide to Time Travel in the Movies is here to help us all make better, more informed decisions when it comes to choosing our time travel movie fare.

    This is not meant to be an exhaustive list; rather, we selected films that represented many diverse approaches to time travel across multiple subgenres and decades. We then evaluated each one—grading on a curve—with regard to its overall entertainment value and scientific logic, with the final combined score determining a film's spot on the overall ranking. For the “science” part of our scoring system, we specifically took three factors into account. First and foremost, does the time travel make logical sense? Second, is the physical mechanism of time travel somewhat realistic? And third, does the film use time travel in narratively interesting ways? So a movie like Looper , which makes absolutely no sense if you think about it too hard, gets points for weaving time paradoxes thoroughly into the fabric of the story.

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      Meet “Amaterasu”: Astronomers detect highest energy cosmic ray since 1991 / ArsTechnica · Thursday, 23 November - 19:00 · 1 minute

    Artist’s illustration of extensive air showers induced by ultra-high-energy cosmic rays. Credit: Toshihiro Fujii/L-INSIGHT/Kyoto University

    Astronomers involved with the Telescope Array experiment in Utah's West Desert have detected an ultra-high-energy cosmic ray (UHECR) with a whpping energy level of 244 EeV, according to a new paper published in the journal Science. It's the most energetic cosmic ray detected since 1991, when astronomers detected the so-called "Oh-My-God' particle , with energies of an even more impressive 320 EeV. Astronomers have dubbed this latest event the "Amaterasu" particle, after the Shinto sun goddess said to have created Japan. One might even call it the "Oh-My-Goddess" particle.

    Cosmic rays are highly energetic subatomic particles traveling through space near the speed of light. Technically, a cosmic ray is just an atomic nucleus made up of a proton or a cluster of protons and neutrons. Most originate from the Sun, but others come from objects outside our solar system. When these rays strike the Earth’s atmosphere, they break apart into showers of other particles (both positively and negatively charged).

    They were first discovered in 1912 by Austrian physicist Victor Hess via a series of ascents in a hydrogen balloon to take measurements of radiation in the atmosphere with an electroscope. He found that the rate of ionization was a good three times the rate at sea level, thereby disproving a competing theory that this radiation came from the rocks of  Earth. If you've ever seen a cloud chamber in a science museum, cosmic ray tracks look like wispy little white lines, similar to tiny jet contrails.

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      In the (convection) zone: Astronomers eavesdrop on stars’ innate “twinkle” / ArsTechnica · Tuesday, 22 August, 2023 - 20:46 · 1 minute

    Visualization of "Twinkle, Twinkle, Little Star" played through three sizes of massive stars. Credit: Northwestern University.

    Science 101 tells us that the twinkling appearance of stars from our vantage point on Earth is due to atmospheric effects: winds and varying temperatures and densities in the air bend and distort the light. But stars have another sort of "twinkle" produced by how gases ripple in waves across their surface, an effect that could provide astronomers with a handy means of exploring the interior of massive stars to learn more about how they form and evolve. But the effect is much too small to be readily detected by telescopes.

    So scientists have now developed the first 3D simulations of that innate twinkle, according to a recent paper published in the journal Nature Astronomy. As a bonus, the researchers converted the data from those rippling waves of gas into an audible sound, so now we can all take a moment to listen to "Twinkle, Twinkle, Little Star" (see video above) and Gustav Holst's "Jupiter" (see video below) in the "language" of the stars.

    “Motions in the cores of stars launch waves like those on the ocean,” said co-author Evan Anders of Northwestern University. “When the waves arrive at the star’s surface, they make it twinkle in a way that astronomers may be able to observe. For the first time, we have developed computer models which allow us to determine how much a star should twinkle as a result of these waves. This work allows future space telescopes to probe the central regions where stars forge the elements we depend upon to live and breathe.”

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      When it comes to keeping the fizz in your champagne, bottle size matters / ArsTechnica · Friday, 28 July, 2023 - 22:59 · 1 minute

    French physicist Gerard Liger-Belair studied CO₂ levels in 13 old champagne vintages in three different bottle sizes.

    Enlarge / French physicist Gerard Liger-Belair studied CO₂ levels in 13 old champagne vintages in three different bottle sizes. (credit: Andy Roberts/Getty Images)

    A large part of the pleasure of imbibing a glass of champagne comes from its effervescence: all those bubbles rising from the glass and ticking the nose and palate. If there's no fizz, there's no fun—and also less flavor and aromas to savor. A recent paper published in the journal ACS Omega found that the size of the champagne bottle is a key factor in determining when the wine inside will go flat.

    As we've reported previously , champagne's effervescence arises from the nucleation of bubbles on the glass walls. Once they detach from their nucleation sites, the bubbles grow as they rise to the liquid surface, where they burst. This typically occurs within a couple of milliseconds, and the distinctive crackling sound is emitted when the bubbles rupture. The bubbles even "ring" at specific resonant frequencies , depending on their size, so it's possible to "hear" the size distribution of bubbles as they rise to the surface in a glass of champagne.

    Prior studies have shown that when the bubbles in champagne burst, they produce droplets that release aromatic compounds believed to enhance the flavor. Larger bubbles enhance the release of aerosols into the air above the glass—bubbles on the order of 1.7 mm across at the surface. French physicist Gerard Liger-Belair of the University of Reims Champagne-Ardenne is one of the foremost scientists studying many different aspects of champagne and has now turned his attention to exploring how long champagne can age in the bottle before the carbonation dissipates to the point where those all-important bubbles can no longer form.

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      The Namibian fairy circle debate rages on: Could it be sand termites after all? / ArsTechnica · Wednesday, 26 July, 2023 - 21:48 · 1 minute

    Fairy circles in the Namib Desert.

    Enlarge / Bare, reddish-hued circular patches in the Namib Desert known as "fairy circles" are also found in northwestern Australia. (credit: UHH/MIN/Juergens)

    Himba bushmen in the Namibian grasslands have long passed down legends about the region's mysterious fairy circles: bare, reddish-hued circular patches that are also found in northwestern Australia. In the last 10 years, scientists have heatedly debated whether these unusual patterns are due to sand termites or to an ecological version of a self-organizing Turing mechanism. Last year, a team of scientists reported what they deemed definitive evidence of the latter, thus ruling out sand termites, but their declaration of victory may have been premature. A recent paper published in the journal Perspectives in Plant Ecology, Evolution, and Systematics offers a careful rebuttal of those 2022 findings, concluding that sand termites may be to blame after all.

    As we've reported previously, the fairy circles can be as large as several feet in diameter. Dubbed "footprints of the gods," it's often said they are the work of the Himba deity Mukuru , or an underground dragon whose poisonous breath kills anything growing inside those circles. Scientists have their own ideas.

    One theory—espoused by study co-author Norbert Jürgens, a biologist at the University of Hamburg in Germany—attributed the phenomenon to a particular species of termite ( Psammmotermes allocerus ), whose burrowing damages plant roots, resulting in extra rainwater seeping into the sandy soil before the plants can suck it up—giving the termites a handy water trap as a resource. As a result, the plants die back in a circle from the site of an insect nest. The circles expand in diameter during droughts because the termites must venture farther out for food.

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      This is the world’s smallest 3D-printed wineglass, Swedish scientists claim / ArsTechnica · Friday, 7 July, 2023 - 20:05 · 1 minute

    The world’s smallest 3D-printed wineglass (left) and an optical resonator for fiber optic telecommunication

    Enlarge / The world’s smallest 3D-printed wineglass in silica glass (left) and an optical resonator for fiber optic telecommunication, photographed with scanning electron microscopy. The rim of the glass is smaller than the width of a human hair. (credit: KTH Royal Institute of Technology)

    A team of Swedish scientists has developed a novel 3D-printing technique for silica glass that streamlines a complicated energy-intensive process. As a proof of concept, they 3D-printed the world's smallest wineglass (made of actual glass) with a rim smaller than the width of one human hair, as well as an optical resonator for fiber optic telecommunications systems—one of several potential applications for 3D-printed silica glass components. They described their new method in a recent paper in the journal Nature Communications.

    “The backbone of the Internet is based on optical fibers made of glass," said co-author Kristinn Gylfason of the KTH Royal Institute of Technology in Stockholm. "In those systems, all kinds of filters and couplers are needed that can now be 3D printed by our technique. This opens many new possibilities.”

    Silica glass (i.e., amorphous silicon dioxide) is one material that remains challenging for 3D printing, particularly at the microscale, according to the authors, though several methods seek to address that challenge, including stereolithography, direct ink writing, and digital light processing. Even those have only been able to achieve feature sizes on the order of several tens of micrometers, apart from one 2021 study that reported nanoscale resolution.

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      Perovskite + silicon solar panels hit efficiencies of over 30% / ArsTechnica · Friday, 7 July, 2023 - 17:58 · 1 minute

    Images of rows of solar panels in a grassy area.

    Enlarge (credit: audioundwerbung )

    In most industrialized countries, solar panels account for only a quarter to a third of the overall cost of building a solar farm. All the other expenses—additional hardware, financing, installation, permitting, etc—make up the bulk of the cost. To make the most of all these other costs, it makes sense to pay a bit more to install efficient panels that convert more of the incoming light into electricity.

    Unfortunately, the cutting edge of silicon panels is already at about 25 percent efficiency, and there's no way to push the material past 29 percent. And there's an immense jump in price between those and the sorts of specialized, hyper-efficient photovoltaic hardware we use in space.

    Those pricey panels have three layers of photovoltaic materials, each tuned to a different wavelength of light. So to hit something in between on the cost/efficiency scale, it makes sense to develop a two-layer device. This week saw some progress in that regard, with two separate reports of two-layer perovskite/silicon solar cells with efficiencies of well above 30 percent. Right now, they don't last long enough to be useful, but they may point the way toward developing better materials.

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      The physics of how gentoo penguins can swim speedily underwater / ArsTechnica · Thursday, 6 July, 2023 - 22:33 · 1 minute

    A gentoo penguin swimming

    Enlarge / Gentoo penguins are the world's fastest swimming birds, thanks to the unique shape and structure of their wings. (credit: Priya Venkatesh/CC BY-SA 3.0 )

    Gentoo penguins are the world's fastest swimming birds, clocking in at maximum underwater speeds of up to 36 km/h (about 22 mph). That's because their wings have evolved into flippers ideal for moving through water (albeit pretty much useless for flying in the air). Physicists have now used computational modeling of the hydrodynamics of penguin wings to glean additional insight into the forces and flows that those wings create underwater. They concluded that the penguin's ability to change the angle of its wings while swimming is the most important variable for generating thrust, according to a recent paper published in the journal Physics of Fluids.

    “Penguins’ superior swimming ability to start/brake, accelerate/decelerate, and turn swiftly is due to their freely waving wings," said co-author Prasert Prapamonthon of King Mongkut‘s Institute of Technology Ladkrabang in Bangkok, Thailand. "They allow penguins to propel and maneuver in the water and maintain balance on land. Our research team is always curious about sophisticated creatures in nature that would be beneficial to mankind.”

    Scientists have long been interested in the study of aquatic animals. Such research could lead to new designs that reduce drag on aircraft or helicopters. Or it can help build more efficient bio-inspired robots for exploring and monitoring underwater environments—such as RoboKrill , a small, one-legged, 3D-printed robot designed to mimic the leg movement of krill so it can move smoothly in underwater environments.

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