Ultracold gas exhibits bizarre quantum behavior
New experiments find weird quantum activity in supercold gas.
26 September, 2020
Credit: Pixabay
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<p>Experiments by California physicists revealed "bizarre" behavior in an ultracold gas. The results promise innovations in quantum engineering and a connection between classical physics and quantum mechanics.</p><p>The scientists used lasers to set up an optical trap for lithium atoms. As they were held in a lattice formation, pulses of energy shook up the system and made the atoms exhibit truly unusual quantum activities.</p><p>The research was carried out by UC Santa Barbara undergraduate student Alec Cao, who was the lead author of the paper, and his colleagues in professor David Weld's <a href="https://www.physics.ucsb.edu/people/david-weld" target="_blank">atomic physics group.</a></p>
<p><span style="background-color: initial;">The scientist's lab specializes in creating <strong>"artificial solids"</strong>, described as "</span><span style="background-color: initial;">low-dimensional lattices of light and ultracold atoms" by the university's <a href="https://www.news.ucsb.edu/2020/020020/quantum-shake" target="_blank">press release.</a> These solids can simulate how quantum particles would behave in dense solids that are subjected to repeating force. The experiments go back to the work of the Nobel laureate physicist <a href="https://en.wikipedia.org/wiki/Felix_Bloch" target="_blank" rel="noopener noreferrer">Felix Bloch</a> for the underpinning. Bloch predicted that if you apply constant force to a quantum particle in a periodic quantum structure, it will start oscillating.</span></p><p>Despite Bloch's theoretical prediction, actual observation of such oscillations didn't happen <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.213201" target="_blank">until 2018</a>, also by Weld's group. </p><p>In the new experiment, they changed laser intensities and outside magnetic forces, creating time dependency and curving the lattice. This established a force field leading to slow oscillations that "gave us the opportunity to look at what happens when you have a Bloch oscillating system in an inhomogenous environment," explained Weld.</p>
Quantum Mechanics, Onions, and a Theory of Everything
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="036ae7b8dd661df2d125a3421a0299ba"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/bcVruA0AJ-o?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>And what happened was quite unexpected, according to the researchers. The atoms were shooting back and forth, moving further apart at various intervals, and even created patterns in reaction to the energy pulses.</p><p style="margin-left: 20px;">"It was a bit bizarre," explained Weld. "Atoms would get pumped in one direction. Sometimes they would get pumped in another direction. Sometimes they would tear apart and make these structures that looked like DNA."</p><p>To explain what they were seeing, the scientists applied <a href="http://www.physics.emory.edu/faculty/weeks/research/tseries7.html" target="_blank">Poincaré sections</a> - a mathematical technique developed for classical physics. </p><p style="margin-left: 20px;">"In our experiment, a time interval is set by how we periodically modify the lattice in time," said Cao. "When we chucked out all the 'in-between' times and looked at the behavior once every period, structure and beauty emerged in the shapes of the trajectories because we were properly respecting the symmetry of the physical system." </p>
<p><span style="background-color: initial;">Professor Weld pointed out that Alec understood that these paths could tell precisely "</span><span style="background-color: initial;">why in some regimes of driving the atoms get pumped, while in other regimes of driving the atoms spread out and break up the wave function."</span></p><p>The research may have applications in topological quantum computing as well as advancing knowledge of how quantum chaos appears, explaining such phenomena as the butterfly effect. </p><p>Check out the new study in <a href="http://dx.doi.org/10.1103/PhysRevResearch.2.032032" target="_blank">Physical Review Research.</a></p>
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Time: Do the past, present, and future exist all at once?
Does time exist? Here's what the debate is all about.
14 September, 2020
- Everything we do as living organisms is dependent, in some capacity, on time. The concept is so complex that scientists still argue whether it exists or if it is an illusion.
- In this video, astrophysicist Michelle Thaller, science educator Bill Nye, author James Gleick, and neuroscientist Dean Buonomano discuss how the human brain perceives of the passage of time, the idea in theoretical physics of time as a fourth dimension, and the theory that space and time are interwoven.
- Thaller illustrates Einstein's theory of relativity, Buonomano outlines eternalism, and all the experts touch on issues of perception, definition, and experience.
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3 wonders of the universe, explained
Astronomer Michelle Thaller schools us on what atoms really look, the Big Bang theory, and the speed of light.
04 September, 2020
- Most people have seen atoms illustrated in textbooks and know about the Big Bang and the speed of light, but there is a good chance what you think you know is not scientifically accurate.
- Michelle Thaller, an astronomer and Assistant Director for Science Communication at NASA, is here to clear up the misconceptions and explain why atoms don't actually look that way, why the Big Bang is a misnomer, and why the speed of light is more than just really fast.
- Is there an edge of space? Does light experience time? Watch this video for answers to those and other interesting questions.
Study shows why face shields don’t work as well as face masks
Some people choose alternatives to masks for comfort. A study shows the difference in effectiveness.
03 September, 2020
Credit: Siddhartha Verma, Manhar Dhanak, John Frankenfield
- A new study provides a visualization of why face shields are ineffective at stopping the spread of COVID-19.
- Using a mannequin that could simulate coughing, the authors demonstrated how water droplets slide around shields.
- The authors conclude that shields are not an effective replacement for masks.
<p>Face masks are everywhere these days, and for very good reason. They are proven to help reduce the chance of spreading COVID-19 by limiting how far water droplets people <a href="https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/coronavirus-mask/art-20485449" target="_blank">exhale can go,</a> and most establishments won't let you in without one. Despite this, complaints about wearing them abound. </p><p>A common and all too human one is that they prevent people from seeing your facial expressions, a key element of human communication. Others protest that masks are uncomfortable, and people who need glasses are quick to tell you that masks often cause glasses to fog. Many have tried using face shields, large plastic screens, in place of a proper mask to avoid these issues.</p><p>While the CDC already stated that face shields are not recommended as a replacement for <a href="https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/cloth-face-cover-guidance.html#masks-with-vents" rel="noopener noreferrer" target="_blank">face masks</a>, a new study offers a visualization of the price you pay in protection in exchange or an ounce of comfort. </p>
A cool, if slightly terrifying, visualization.
<p>The straightforwardly named "<a href="https://aip.scitation.org/doi/pdf/10.1063/5.0022968" target="_blank"><em>Visualizing droplet dispersal for face shields and masks with exhalation valves</em></a><em>" </em>was published in the journal "<a href="https://aip.scitation.org/journal/phf" target="_blank">Physics of Fluids</a>" and led by Dr. Siddhartha Verma of Florida Atlantic University. In it, the researchers explain that while face shields are very good at blocking the forward motion of larger droplets of water, the large open space in their design allows for smaller droplets to pass them and disperse throughout the room, reducing their potential benefits.</p><p>The authors attached a face shield to a slightly modified mannequin that could simulate coughing to demonstrate this. Small droplets of water and glycerin, comparable in size to the lower end of estimates of what is needed for a virus to travel, were blown through the mannequin's mouth and highlighted with laser sheets as they traveled throughout the room. </p> As illustrated below, small droplets that stop moving forward do not immediately drop to the floor, but instead, they float toward the gap at the bottom of the shield. Following air currents, the droplets eventually made their way around the face shield and began to spread. Given enough time, they'll spread up to a few feet away.<iframe width="750" height="423" src="https://www.youtube.com/embed/JEy1cF2pMdM" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe><p>Dr. Verma explained the weaknesses of face shields to the <a href="https://www.nytimes.com/2020/09/01/well/live/face-shields-masks-valves-vents.html" target="_blank">New York Times</a>:</p><p>"Masks act as filters and actually capture the droplets and any other particles we expel. Shields are not able to do that. If the droplets are large they will be stopped by the plastic shield. But if they are aerosol sized, 10 microns or smaller, they'll just escape from the sides or the bottom of the shield. Everything that is expelled will very likely get distributed in the room."</p><p>The authors note that the water droplets' concentration is reduced by wearing a face shield, meaning that fewer droplets are spread than would be spread by a person without any protection. The benefits of this are limited, though, and a previous study carried out by the authors of this test also shows how much more effective proper face masks are than face <a href="https://aip.scitation.org/doi/10.1063/5.0016018" target="_blank">shields</a>. Another study from 2014 gives face shields a mere 23 percent efficiency at reducing the inhalation of such <a href="https://www.tandfonline.com/doi/full/10.1080/15459624.2013.877591" target="_blank" rel="noopener noreferrer">droplets</a>. </p><p>It should be no surprise, then, that the study concludes that face masks are preferable to face shields when it comes to slowing the spread of COVID-19.</p><p>The study also considered face masks with exhaust values, as shown in the final test in the above video. Face masks with exhaust values allow unfiltered droplets to go through the valve. Why they don't do much to prevent droplets from spreading everywhere is obvious. Just as with face shields, the droplets that are initially unable to move forward eventually manage to get to the same place through dispersion. </p>
Why you should wear a proper facemask, revisited.
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="232361a0d3ad7a620c9ad6d8eec8fa50"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/UFX9oS2kpUA?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>The shortcomings of face shields and other mask alternatives are not shared by the thing they are meant to replace, the basic, well-made face mask.</p><p>As explained above, face masks work to keep others around you from getting your germs by keeping the water droplets you exhale, which may contain viruses, from <a href="https://www.ucsf.edu/news/2020/06/417906/still-confused-about-masks-heres-science-behind-how-face-masks-prevent" target="_blank">spreading</a>. They have also been shown to reduce the number of droplets from other people's breath that reach your face, potentially preventing you from getting <a href="https://www.npr.org/sections/health-shots/2020/06/21/880832213/yes-wearing-masks-helps-heres-why" target="_blank" rel="noopener noreferrer">sick</a>. Given that face masks lack a large hole in them, as shields or masks with valves do, they allow far fewer droplets to escape than the competition. </p><p>The study considered the differences between a cheaply made face mask and a well-made one, with the cheap one proving much less effective. Even the best masks have some degree of leakage, so maintaining social distancing of at least two meters (about six feet) is still necessary. </p><p>No protective mask is perfect, and no set of rules offers complete safety. However, some objects and procedures work better than others at keeping people safe. As this study shows, face shields, masks with exhaustion valves, and cheaply made masks don't work as well as a well-made face mask.</p>
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The Earth may have been wet from the very start
A new study finds the rocks that first formed Earth carried with them enough hydrogen for three times the water we have today.
02 September, 2020
Credit: NASA
- Enstatite chondrite meteorites are rare today, but they may have been Earth's basic building blocks.
- A study finds these meteorites contain a surprising amount of hydrogen, nitrogen, and water.
- The implication of the study is that Earth had all of its water from the beginning.
<p>Very few <a href="http://www.meteorlab.com/METEORLAB2001dev/enstchon.htm" target="_blank">enstatite chondrite</a> ("E chondrite") meteorites have been found on Earth — there are less than 200 specimens, about 2 percent of all the meteorites that have been found.</p><p>Rare as they are today, though, it may be that Earth and enstatite chondrites go way back. The rocks are isotopically identical to the Earth — something that's strikingly unusual — and this has led some to theorize that these may be the very type of early solar system rocks that first <a href="https://www.researchgate.net/publication/222548941_The_chemical_composition_of_the_Earth_Enstatite_chondrite_models" target="_blank">clumped together to form the Earth</a>.</p><p>E chondrites have generally been considered to be dry rocks, formed as they were in the hot center of the early solar system. However, a new study of pristine samples by researchers from <a href="http://www.crpg.cnrs-nancy.fr/index.php" target="_blank" rel="noopener noreferrer">Centre de Recherches Pétrographiques et Géochimiques</a> (CPRG) in Nancy, France reveals that they contain a stunningly high amount of hydrogen and even some water.</p><p>Putting 2 + 2 together:</p><p style="margin-left: 20px;">"If enstatite chondrites were effectively the building blocks of our planet — as strongly suggested by their similar isotopic compositions — this result implies that these types of chondrites supplied enough water to Earth to explain the origin of Earth's water, which is amazing!" — study co-author, physicist <a href="https://scholar.google.fr/citations?user=YxjHY7wAAAAJ&hl=fr" target="_blank">Lionel G. Vacher</a> of Washington University in St. Louis</p><p>The researchers calculate that there would have been enough hydrogen in Earth-forming E chondrites to supply three times the amount of water we currently have in our oceans. That means the Earth was wet from the start, or at least as soon as its E chondrite got far enough away from the Sun for the hydrogen it contains to condense into water.</p><p>The research is published in the journal <a href="https://science.sciencemag.org/content/369/6507/1110" target="_blank" rel="noopener noreferrer">Science</a>.</p>
Analyzing E chondrites
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzYwNDUwOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNzc0NTg1M30.uL0ziiPPOTZud7L_5IXJt2hEKhiX42qcgKoyb9ADOiE/img.jpg?width=980" id="4d974" class="rm-shortcode" data-rm-shortcode-id="3692b2cf3dcba948cedc8c8d42c7a244" data-rm-shortcode-name="rebelmouse-image" alt="enstatite chondrite" />Credit: User Captmondo/Wikimedia
<p>Lead author <a href="http://recherche.crpg.cnrs-nancy.fr/spip.php?rubrique437&lang=fr" target="_blank">Laurette Piani</a> of CPRG <a href="https://source.wustl.edu/2020/08/meteorite-study-suggests-earth-may-have-always-been-wet/" target="_blank">says</a>, "Only a few pristine enstatite chondrites exist: ones that were not altered on their asteroid nor on Earth." In acquiring samples for study, the researchers went out of their way <em>not</em> to select meteorites holding water: "In our study we have carefully selected the enstatite chondrite meteorites and applied a special analytical procedure to avoid being biased by the input of terrestrial water."</p><p>As to why this team of scientists were the first to identify high concentrations of hydrogen in E chondrites, Piani suggests it's due to previous researchers' bias, saying, "it was commonly assumed that these chondrites formed close to the sun. Enstatite chondrites were thus commonly considered 'dry,' and this frequently reasserted assumption has probably prevented any exhaustive analyses to be done for hydrogen." </p><p>Using conventional <a href="https://en.wikipedia.org/wiki/Mass_spectrometry" target="_blank">mass spectrometry</a> and secondary ion mass spectrometry, the scientists did also find water in the meteorites. Recalls Vacher, "The most interesting part of the discovery for me is that enstatite chondrites, which were believed to be almost 'dry,' contain an unexpectedly high abundance of water." In addition to water, the team found substantial amounts of nitrogen they theorize could have aided in the formation of the Earth's atmosphere, nitrogen being its most abundant element.</p>Earth's first sip
<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzYwNDUyMy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1NzM4OTQzMn0.-bEMCDbsCNLfE6A-weKvSN4e8nLeb9wmyNTwXD26XZo/img.jpg?width=980" id="b95b9" class="rm-shortcode" data-rm-shortcode-id="a70443a22a624a53b43a6b335c054240" data-rm-shortcode-name="rebelmouse-image" alt="ocean" />Credit: gunsan gimbanjang/Shutterstock
<p>The researchers were also able to add fresh evidence supporting the theory that E chondrites were Earth's basic building blocks: The meteorites' hydrogen and nitrogen isotopes turned out to be the same as the planet's.</p><p>"Our discovery shows," says Piani, "that the Earth's building blocks might have significantly contributed to the Earth's water. Hydrogen-bearing material was present in the inner solar system at the time of the rocky planet formation, even though the temperatures were too high [at the time] for water to condense." </p><p>Where did our water come from? It was always right here.</p>
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