Physicists have proposed a new kind of atomic clock based on a revived superradiant laser concept that could produce an extraordinarily stable signal with a linewidth around 100 microhertz, potentially the narrowest ever for an optical laser. "The implications of this result could stretch well beyond timekeeping," reports Phys.org. "A laser immune to environmental frequency shifts would be a powerful tool in optical interferometry -- using interference patterns in light to make ultra-precise measurements." From the report: In a conventional laser, a mirrored cavity bounces light back and forth between atoms, building up a bright, coherent beam. A superradiant laser works differently: rather than relying on the cavity to maintain coherence, the atoms themselves act as single coordinated emitters, collectively synchronizing their light emission. Following early theoretical ideas emerged in the 1990s, the concept didn't gain concrete traction until 2008, when researchers at the University of Colorado proposed that superradiant lasers could serve as a new kind of atomic clock. Atomic clocks work by using laser light to probe a very precise transition in an atom, causing electrons to transition between energy levels at an extraordinarily stable frequency. Because a superradiant laser stores its coherence in the atoms rather than the cavity, its output frequency is far less vulnerable to environmental disturbances like vibrations or temperature fluctuations. Yet although this concept was first demonstrated experimentally in 2012 in a pulsed regime, the influence of heating has so far held superradiant lasers back from their full potential. To keep the laser running continuously as an atomic clock requires, atoms must be constantly replenished with energy. Doing this atom-by-atom delivers random kicks that heat the atomic sample and disrupt the lasing process, confining it to brief pulses rather than a steady beam. In their study, Reilly's team considered whether a modification to earlier theoretical concepts could make a continuous laser suitable for an atomic clock. In almost all previous studies, atoms were treated as simple two-level systems: an electron sitting in a ground state, occasionally jumping up to an excited state and back again. The team proposed that the heating problem could be solved by adding one extra ground state to the picture. In a two-level system, if both the pumping (re-energizing) and decay processes happen collectively through the cavity, the mathematics constrains the system in a way that prevents stable, continuous lasing. But with three levels available, pumping and decay can operate on entirely separate transitions, breaking that constraint and allowing the collective approach to work. The findings have been published in the journal Physical Review Letters.

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Wow... des scientifiques du NIST ont réussi à créer un laser capable d'émettre différentes longueurs d'onde. Et à les miniaturiser.
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Slashdot reader smazsyr writes: A new review says we've had fructose wrong for decades. The nine authors, led by Richard Johnson at the University of Colorado Anschutz, argue that fructose "is not just another calorie." It is a signal. It tells the liver to make fat and brace for a famine that never comes. That made sense for a bear fattening up on autumn berries. It makes less sense for a person drinking soda in March. The review reframes the WHO's sugar guideline, argues ScienceBlog.com, as "less a recommendation about calories and more a warning about a signalling molecule we have been dosing ourselves with, several times a day, for most of a century."

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An anonymous reader quotes a report from the Guardian: The critical Atlantic current system appears significantly more likely to collapse than previously thought after new research found that climate models predicting the biggest slowdown are the most realistic. Scientists called the new finding "very concerning" as a collapse would have catastrophic consequences for Europe, Africa and the Americas. The Atlantic meridional overturning circulation (Amoc) is a major part of the global climate system and was already known to be at its weakest for 1,600 years as a result of the climate crisis. Scientists spotted warning signs of a tipping point in 2021 and know that the Amoc has collapsed in the Earth's past. Climate scientists use dozens of different computer models to assess the future climate. However, for the complex Amoc system, these produce widely varying results, ranging from some that indicate no further slowdown by 2100 to those suggesting a huge deceleration of about 65%, even when carbon emissions from fossil fuel burning are gradually cut to net zero. The research combined real-world ocean observations with the models to determine the most reliable, and this hugely reduced the spread of uncertainty. They found an estimated slowdown of 42% to 58% in 2100, a level almost certain to end in collapse. The Amoc is a major part of the global climate system and brings sun-warmed tropical water to Europe and the Arctic, where it cools and sinks to form a deep return current. A collapse would shift the tropical rainfall belt on which many millions of people rely to grow their food, plunge western Europe into extreme cold winters and summer droughts, and add 50-100cm to already rising sea levels around the Atlantic. The slowdown has to do with the Arctic's rapidly rising temperatures from global warming. "Warmer water is less dense and therefore sinks into the depths more slowly," explains the Guardian. "This slowing allows more rainfall to accumulate in the salty surface waters, also making it less dense, and further slowing the sinking and forming an Amoc feedback loop." The new research has been published in the journal Science Advances.

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An anonymous reader quotes a report from the Guardian: We may appear to have little in common with sperm whales – enormous, ocean-dwelling animals that last shared a common ancestor with humans more than 90 million years ago. But the whales' vocalized communications are remarkably similar to our own, researchers have discovered. Not only do sperm whale have a form of "alphabet" and form vowels within their vocalizations but the structure of these vowels behaves in the same way as human speech, the new study has found. Sperm whales communicate in a series of short clicks called codas. Analysis of these clicks shows that the whales can differentiate vowels through the short or elongated clicks or through rising or falling tones, using patterns similar to languages such as Mandarin, Latin and Slovenian. The structure of the whales' communication has "close parallels in the phonetics and phonology of human languages, suggesting independent evolution," the paper, published in the Proceedings B journal, states. Sperm whale coda vocalizations are "highly complex and represent one of the closest parallels to human phonology of any analyzed animal communication system," it added. [...] The new study shows that "sperm whale communication isn't just about patterns of clicks -- it involves multiple interacting layers of structure," said Mauricio Cantor, a behavioral ecologist at the Marine Mammal Institute who was not involved in the research. "With this study, we're starting to see that these signals are organized in ways we didn't fully appreciate before." The latest discovery around sperm whale speech has inched forward the possibility of someday fully understanding the creatures and even communicating with them. Project CETI has set a goal of being able to comprehend 20 different vocalized expressions, relating to actions such as diving and sleeping, within the next five years. A future where we're able to fully understand what the whales are saying and be able to have a conversation with them is "totally within our grasp," said David Gruber, founder and president of Project CETI. "We've already got a lot further than I thought we could. But it will take time, and funding. At the moment we are like a two-year-old, just saying a few words. In a few years' time, maybe we will be more like a five-year-old."

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Researchers say the world's largest known wild chimpanzee community in Uganda fractured into rival factions and has been locked in a vicious "civil war" for the last eight years. "It is not clear exactly why the once close-knit community of Ngogo chimpanzees at Uganda's Kibale National Park are at loggerheads, but since 2018 the scientists have recorded 24 killings, including 17 infants," reports the BBC. From the report: [O]ver several decades, [lead author Aaron Sandel] said the nearly 200 Ngogo chimpanzees had lived in harmony. There were divided into two sets - known to researchers as Western and Central - but they had existed overall as a cohesive group. Sandel said he first noticed them polarizing in June 2015, when the Western chimpanzees ran away and were chased by the Central group. "Chimpanzees are sort of melodramatic," he said, explaining that following arguments there would ordinarily be "screaming and chasing" and then later, they would grooming and co-operating. But following the 2015 dispute, the researchers saw that there was a six-week avoidance period between the two sets, with interactions becoming more infrequent. When they did occur, Sandel said they were "a little more intense, a little more aggressive." Following the emergence of the two distinct groups in 2018, members of the Western group started attacking the Central chimpanzees. In 24 targeted attacks since the split, at least seven adult males and 17 infants from the Central chimps have been killed, the study found, although the researchers believe the actual number of deaths are higher. The researchers believe many factors such as the group size and subsequent competition of resources, and "male-male competition" for reproducing may be to blame. But they say there were three likely catalysts: - The first, were the deaths of five adult males and one adult female -- for reasons unknown -- in 2014, which could have disrupted social networks and weakened social ties across the subgroups - The following year, there was a change in the alpha male, which the study says coincided with the first period of separation between the Western and Central groups. "Changes in the dominance hierarchy can increase aggression and avoidance in chimpanzees," it explained - The third factor was the deaths of 25 chimpanzees, including four adult males and 10 adult females, as a result of a respiratory epidemic, in 2017, a year before the final separation. One of the adult males who died was "among the last individuals to connect the groups," the research paper said. The study has been published in the journal Science.

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