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Yahoo
5 days ago
- General
- Yahoo
Physicists capture 'second sound' for the first time — after nearly 100 years of searching
When you buy through links on our articles, Future and its syndication partners may earn a commission. Scientists have captured direct images of heat behaving like sound — an elusive phenomenon called 'second sound' — for the very first time. Imaged within an exotic superfluid state of cold lithium-6 atoms by a new heat-mapping technique, the phenomenon shows heat moving as a wave, bouncing like sound around its container. Understanding the way that second sound moves could help scientists predict how heat flows inside ultradense neutron stars and high-temperature superconductors — one of the "holy grails" of physics whose development would enable near-lossless energy transmission. The researchers published their findings in the journal Science. "It's as if you had a tank of water and made one half nearly boiling," study co-author Richard Fletcher, an assistant professor of physics at Massachusetts Institute of Technology (MIT), said in a statement. "If you then watched, the water itself might look totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks totally still." Typically heat spreads from a localized source, slowly dissipating across an entire material as it raises the temperature across it. But exotic materials called superfluids needn't play by these rules. Created when clouds of fermions (which include protons, neutrons and electrons) are cooled to temperatures approaching absolute zero, atoms inside superfluids pair up and travel frictionlessly throughout the material. Related: Physicists make record-breaking 'quantum vortex' to study the mysteries of black holes As a result, heat flows differently through the material: instead of spreading through the movements of particles within the fluid, as it typically flows, heat sloshes back and forth within superfluids like a sound wave. This second sound was first predicted by the physicist László Tisza in 1938, but heat-mapping techniques have, until now, proven unable to observe it directly. "Second sound is the hallmark of superfluidity, but in ultracold gases so far you could only see it in this faint reflection of the density ripples that go along with it," study senior-author Martin Zwierlein, a professor of physics at MIT, said in the statement. "The character of the heat wave could not be proven before." To capture second sound, the researchers had to solve a daunting problem in tracking the flow of heat inside ultracold gases. These gases are so cold that they do not give off infrared radiation, upon which typical heat-mapping, or thermography, techniques rely. Instead, the physicists developed a method to track the fermion pairs through their resonant frequencies. Lithium-6 atoms resonate at different radio frequencies as their temperatures change, with warmer atoms vibrating at higher frequencies. RELATED STORIES — Scientists turn light into a 'supersolid' for the 1st time ever: What that means, and why it matters — Government scientists discover new state of matter that's 'half ice, half fire' — Scientists unveil new type of 'time crystal' that defies our traditional understanding of time and motion By applying resonant radio frequencies corresponding to warmer atoms, the scientists made these atoms ring in response, enabling them to track the particles' flow frame by frame. "For the first time, we can take pictures of this substance as we cool it through the critical temperature of superfluidity, and directly see how it transitions from being a normal fluid, where heat equilibrates boringly, to a superfluid where heat sloshes back and forth," Zwierlein said. The physicists say that their groundbreaking technique will enable them to better study the behaviors of some of the universe's most extreme objects, such as neutron stars, and measure the conductivity of high-temperature superconductors to make even better designs. "There are strong connections between our puff of gas, which is a million times thinner than air, and the behavior of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars," Zwierlein said. "Now we can probe pristinely the temperature response of our system, which teaches us about things that are very difficult to understand or even reach."
Daily Mail
12-05-2025
- Science
- Daily Mail
Scientists reveal exact date universe will end: 'Sooner than we feared'
Scientists have discovered that the universe is decaying much faster than they thought, and have pinpointed exactly when it will perish. A team of researchers from Radboud University in the Netherlands determined that all the stars in the universe will go dark in one quinvigintillion years. That's a one followed by 78 zeros. But this is a much shorter amount of time than the previous prediction of 10 to the power of 1,100 years, or a one followed by 1,100 zeros. The process they believe is driving the death of the universe is related to Hawking radiation, where black holes emit radiation as they gradually 'evaporate' into nothing. This was thought to be a phenomenon exclusive to black holes, but the researchers showed that things like neutron stars and white dwarfs can also evaporate similarly to black holes. Both neutron stars and white dwarfs are the final stage of a star's life cycle. Massive stars explode into supernovas and then collapse into neutron stars, whereas smaller stars like our sun devolve into white dwarfs. These 'dead' stars can persist for an extremely long time. But according to the researchers, they gradually dissipate and explode once they become too unstable. In other words, knowing how long it takes for a neutron star or a white dwarf to die helps scientists understand the maximum lifespan of the universe, because these will be the last stars to die out. Previous studies did not take Hawking radiation into account, and therefore overestimated the maximum lifespan of the universe, according to lead researcher Heino Falcke, professor of radio astronomy and astroparticle physics at Radboud University. Falcke and his colleagues sought to correct this by calculating how long it takes for neutron stars and white dwarfs to decay via a Hawking-radiation-like process, finding that it takes one quinvigintillion years. 'So the ultimate end of the universe comes much sooner than expected, but fortunately it still takes a very long time,' he said in a statement. In 1975, renowned physicist Stephen Hawking proposed that particles and radiation could escape from a black hole, which contradicted the widely-held belief that nothing escapes the gravitational pull of these extremely massive objects. But according to Hawking, two temporary particles can form at the edge of a black hole. Before they can merge, one particle is sucked back into the black hole and the other escapes. These escaped particles are Hawking radiation. As more and more of these particles escape over time, the black hole gradually decays. This also contradicts Albert Einstein's theory of relativity, which states that black holes can only grow. The team used their 2023 study, published in the journal Physical Review Letters, to lay the groundwork for the recent discovery. In the previous work, Falcke and his colleagues showed that all objects with a gravitational field should be able to evaporate via a similar process. What's more, their calculations suggested that the evaporation rate depends only on the object's density. From there, applying the concept of Hawking radiation to neutron stars and white dwarfs for their new study was relatively straightforward. Those findings have been accepted for publication by the Journal of Cosmology and Astroparticle Physics, but are currently housed on the pre-print server arXiv. Even though these new calculations cut an inconceivable number of years off the universe's lifespan, it doesn't change the fact that humans don't have to worry about the end of everything anytime soon. But they do offer a new look at Hawking's controversial theory. 'By asking these kinds of questions and looking at extreme cases, we want to better understand the theory, and perhaps one day, we will unravel the mystery of Hawking radiation,' said co-author Walter van Suijlekom, professor of mathematics at Radboud University.
