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‘Dancing’ raisins − a simple kitchen experiment reveals how objects can extract energy from their environment and come to life



theconversation.com – Saverio Eric Spagnolie, Professor of Mathematics, of Wisconsin- – 2024-05-13 07:29:32

Surface bubble growth can lift objects upward against gravity.

Saverio Spagnolie

Saverio Eric Spagnolie, University of Wisconsin-Madison

Scientific discovery doesn't always require a high-tech laboratory or a hefty budget. Many people have a first-rate lab right in their own homes – their kitchen.


The kitchen offers plenty of opportunities to view and explore what physicists call soft matter and complex fluids. Everyday phenomena, such as Cheerios clustering in milk or rings left when drops of coffee evaporate, have led to discoveries at the intersection of physics and chemistry and other tasteful collaborations between food scientists and physicists.

Two , Sam Christianson and Carsen Grote, and I published a new study in Nature Communications in May 2024 that dives into another kitchen observation. We studied how objects can levitate in carbonated fluids, a phenomenon that's whimsically referred to as dancing raisins.

The study explored how objects like raisins can rhythmically move up and down in carbonated fluids for several minutes, even up to an hour.

An accompanying Twitter thread about our research went viral, amassing over half a million views in just two days. Why did this particular experiment catch the imaginations of so many?


Bubbling physics

Sparkling water and other carbonated beverages fizz with bubbles because they contain more gas than the fluid can – they're “supersaturated” with gas. When you open a bottle of champagne or a soft drink, the fluid pressure drops and CO₂ molecules begin to make their escape to the surrounding air.

Bubbles do not usually form spontaneously in a fluid. A fluid is composed of molecules that like to stick together, so molecules at the fluid boundary are a bit unhappy. This results in surface tension, a force which seeks to reduce the surface area. Since bubbles add surface area, surface tension and fluid pressure normally squeeze any forming bubbles right back out of existence.

But rough patches on a container's surface, like the etchings in some champagne glasses, can protect new bubbles from the crushing effects of surface tension, offering them a chance to form and grow.


Bubbles also form inside the microscopic, tubelike cloth fibers left behind after wiping a glass with a towel. The bubbles grow steadily on these tubes and, once they're big enough, detach and float upward, carrying gas out of the container.

But as many champagne enthusiasts who put fruits in their glasses know, surface etchings and little cloth fibers aren't the only places where bubbles can form. Adding a small object like a raisin or a peanut to a sparkling drink also enables bubble growth. These immersed objects act as alluring new surfaces for opportunistic molecules like CO₂ to accumulate and form bubbles.

And once enough bubbles have grown on the object, a levitation act may be performed. Together, the bubbles can lift the object up to the surface of the liquid. Once at the surface, the bubbles pop, dropping the object back down. The then begins again, in a periodic vertical dancing motion.

Dancing raisins

Raisins are particularly good dancers. It takes only a few seconds for enough bubbles to form on a raisin's wrinkly surface before it starts to rise upward – bubbles have a harder time forming on smoother surfaces. When dropped into just-opened sparkling water, a raisin can dance a vigorous tango for 20 minutes, and then a slower waltz for another hour or so.


Anyone with a few kitchen staples can do their own dancing raisins experiment.

We found that rotation, or spinning, was critically important for coaxing large objects to dance. Bubbles that cling to the bottom of an object can keep it aloft even after the top bubbles pop. But if the object starts to spin even a little bit, the bubbles underneath make the body spin even faster, which results in even more bubbles popping at the surface. And the sooner those bubbles are removed, the sooner the object can get back to its vertical dancing.

Small objects like raisins do not rotate as much as larger objects, but instead they do the twist, rapidly wobbling back and forth.

Modeling the bubbly flamenco

In the paper, we developed a mathematical model to predict how many trips to the surface we would expect an object like a raisin to make. In one experiment, we placed a 3D-printed sphere that acted as a model raisin in a glass of just-opened sparkling water. The sphere traveled from the bottom of the container to the top over 750 times in one hour.

The model incorporated the rate of bubble growth as well as the object's shape, size and surface roughness. It also took into account how quickly the fluid loses carbonation based on the container's geometry, and especially the flow created by all that bubbly activity.


Small objects covered in bubbles in carbonated water move upwards towards the surface and back down.

Bubble-coated raisins ‘dance' to the surface and plummet once their lifting agents have popped.

Saverio Spagnolie

The mathematical model helped us determine which forces influence the object's dancing the most. For example, the fluid drag on the object turned out to be relatively unimportant, but the ratio of the object's surface area to its volume was critical.

Looking to the future, the model also provides a way to determine some hard to measure quantities using more easily measured ones. For example, just by observing an object's dancing frequency, we can learn a lot about its surface at the microscopic level without having to see those details directly.

Different dances in different theaters

These results aren't just interesting for carbonated beverage lovers, though. Supersaturated fluids exist in nature, too – magma is one example.


As magma in a volcano rises closer to the Earth's surface, it rapidly depressurizes, and dissolved gases from inside the volcano make a dash for the exit, just like the CO₂ in carbonated water. These escaping gases can form into large, high-pressure bubbles and emerge with such force that a volcanic eruption ensues.

The particulate matter in magma may not dance in the same way raisins do in soda water, but tiny objects in the magma may affect how these explosive play out.

The past decades have also seen an eruption of a different kind – thousands of scientific studies devoted to active matter in fluids. These studies look at things such as swimming microorganisms and the insides of our fluid-filled cells.

Most of these active do not exist in water but instead in more complicated biological fluids that contain the energy necessary to produce activity. Microorganisms absorb nutrients from the fluid around them to continue swimming. Molecular motors carry cargo along a superhighway in our cells by pulling nearby energy in the form of ATP from the environment.


Studying these systems can scientists learn more about how the cells and bacteria in the human body function, and how life on this planet has evolved to its current .

Meanwhile, a fluid itself can behave strangely because of a diverse molecular composition and bodies moving around inside it. Many new studies have addressed the behavior of microorganisms in such fluids as mucus, for instance, which behaves like both a viscous fluid and an elastic gel. Scientists still have much to learn about these highly complex systems.

While raisins in soda water seem fairly simple when with microorganisms swimming through biological fluids, they offer an accessible way to study generic features in those more challenging settings. In both cases, bodies extract energy from their complex fluid environment while also affecting it, and fascinating behaviors ensue.

New insights about the physical world, from geophysics to biology, will continue to emerge from tabletop-scale experiments – and perhaps from right in the kitchen.The Conversation

Saverio Eric Spagnolie, Professor of Mathematics, University of Wisconsin-Madison


This article is republished from The Conversation under a Creative Commons license. Read the original article.

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US participation in space has benefits at home and abroad − reaping them all will require collaboration



theconversation.com – Cheyenne Black, Graduate Research Assistant in the Institute for Public Policy Research and Analysis, University of Oklahoma – 2024-05-22 07:24:32

“Cosmic cliffs” in the Carina nebula, captured by the James Webb Telescope.


Cheyenne Black, University of Oklahoma

When people think about what we get from the U.S. space program, it may be along the lines of NASA technology spin-offs such as freeze-dried food and emergency space blankets.


But space activities do much more that benefits life on Earth. Research in space helps scientists study our , develop new technologies, create jobs, grow the economy and foster international collaboration.

Of course, with reports of Russia developing an anti-satellite nuclear weapon, members of Congress and the media have focused their attention on space defense and military readiness.

This is critical, but there are still many other benefits to reap from space. Getting the most out of U.S. space involvement will require collaborating across various social, environmental, commercial, governmental, international and technological backgrounds.

As a space policy scholar focused on private-public partnerships, networks and coalitions, I've seen that policymakers can get the most out of U.S. space endeavors if they invite a wide array of experts into policy discussions.


Benefits on Earth

NASA satellites play a crucial role in documenting changes in global temperatures, sea-level rise, arctic ice extent and air quality. Satellites have also been collecting data for almost 50 years to monitor water use, crop health and crop production. These long-term observations help researchers track environmental changes across the globe.

Space research provides a wide array of technologies in addition to rockets and Moon landers. Cellphone cameras, CAT scanners, the computer mouse, laptops, wireless headsets and water purification systems are just a few public goods NASA has generated.

These spin-off technologies come from NASA's partnerships with private firms, which subsequently make scientific discoveries widely available and accessible.

Growing the space economy

Experts predict that the space sector will continue driving the development of nonspace industries. Agriculture, energy, mining, transportation and pharmaceuticals are just some of the sectors that benefit through spin-off technologies and space-based research.


For example, scientists can conduct experiments on the International Space Station using the microgravity of space to study the chemistry of , improve medications and test cancer treatments.

More and individuals than ever share a vested interest in the space sector's . Experts anticipate the global space economy – the resources used in space for activities – and research and will continue to grow to a market of US$1.4 trillion by 2030.

Commercialization policies opened U.S. space activities to the private sector. This has led to partnerships with companies, such as SpaceX, Blue Origin and others, that are growing the space economy.

These companies have increasingly launched rockets and deployed satellites in recent years. This has increased the need for workers, both in manufacturing positions and specialized STEM roles. Additionally, private companies and universities are partnering to develop various technologies, such as landing systems for a U.S. return to the Moon.


A cylindrical rocket emitting a plume of flame launches upwards in a haze of smoke.

SpaceX's Starship rocket launched in March 2024. More commercial companies, like SpaceX, have partnered with NASA in recent years.

AP Photo/Eric Gay

Communities that host space industry centers have seen economic and educational benefits. For example, Huntsville, Alabama, home of the Marshall Space Flight Center and the U.S. Space and Rocket Center, has attracted an educated workforce with one of the highest rates of engineers per capita. Almost half of residents over the age of 25 in Huntsville have a bachelor's degree or higher.

An aerial view of three buildings.

The Marshall Space Flight Center in Huntsville, Ala.


This rate starkly contrasts with the national average, where 37% have at least a bachelor's degree, and the state's 27% average. Additionally, Huntsville's annual median household income is $8,000 higher than the Alabama average.


Since 1982, Huntsville has also hosted over 750,000 students at the U.S. Space and Rocket Center space camp. This camp educates about science, technology, engineering and leadership to prepare them for a potential future STEM career.

International collaboration

Space also provides an opportunity for the U.S. to collaborate with other countries.

For example, the U.S. works jointly with Italy to observe the impacts of air quality on human . The James Webb Space Telescope, a result of partnerships between NASA, the European Space Agency and the Canadian Space Agency, allows scientists to peer into previously unobserved parts of the cosmos. International collaboration has also established the Artemis Accords, a set of principles agreed to by 40 countries for peaceful, sustainable and transparent cooperation in space.

Getting the most out of space

Right now, U.S. space policymaking occurs at the federal and international level. And while people outside of the government can act as witnesses during congressional hearings or through advocacy groups, that involvement may not be enough to represent the wide spectrum of viewpoints and interests in space policy.


There are a few ways policymakers can input from different stakeholders. These might include inviting more experts from various policy to provide recommendations in congressional hearings, collaborating with advocacy coalitions to create sustainable policies, strengthening and expanding private-public partnerships, and setting a space agenda that emphasizes research and development.The Conversation

Cheyenne Black, Graduate Research Assistant in the Institute for Public Policy Research and Analysis, University of Oklahoma

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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TikTok law threatening a ban if the app isn’t sold raises First Amendment concerns



theconversation.com – Anupam Chander, Professor of and Technology, Georgetown – 2024-05-21 07:25:32

TikTok users worry about losing their social platform, but First Amendment rights are on the line, too.

AP Photo/Ted Shaffrey

Anupam Chander, Georgetown University and Gautam Hans, Cornell University

TikTok, the short-video company with Chinese roots, did the most American thing possible on May 7, 2024: It sued the U.S. government, in the person of Merrick Garland, in federal court. The suit claims the federal law that took effect on April 24, 2024, banning TikTok unless it sells itself violates the U.S. Constitution.


The law names TikTok and its parent company, ByteDance Ltd., specifically. It also applies to other applications and websites reaching more than a million monthly users that allow people to share information and that have ownership of 20% or more from China, Russia, Iran or North Korea. If the president determines that such applications or websites “present a significant threat to the national security,” then those apps and websites, too, must either be sold or banned from the U.S.

TikTok's suit says that the law violates the First Amendment by failing to provide evidence of the national security threat posed by the app and for failing to seek a less restrictive remedy. Despite legislators' claims to the contrary, the law forcing the divestiture of TikTok – the Protecting Americans from Foreign Adversary Controlled Applications Act – implicates First Amendment interests. In our view, it does so in ways that ripple beyond this specific case.

As a company incorporated in the United States that provides an online publishing platform, TikTok has a right protected by the First Amendment to select what messages – in this case, user – it chooses to publish.

A ban appears to us, scholars who study law and technology, to be a massive prior restraint, which is generally barred by U.S. courts. Prior restraint is action by the to prevent speech, typically some form of publication, before it occurs.


The First Amendment limits what the government can do to censor speech.

Speech in the crosshairs

The law's backers say that it is not a ban – all TikTok has to do is sell itself. These supporters describe the bill as a divestiture, a purely economic regulation that they say should insulate it from First Amendment . After the sale, users could happily keep on using TikTok, not caring who owns the company. But the law seems to us an attempt to control speech by mandating a change in ownership.

Changing the speech content on the app is the express goal of some of the law's backers. The principal author of the bill, former U.S. Rep. Mike Gallagher, who stepped down from office in April to join a venture capital firm partly backed by Microsoft, explained to The New York Times that he was principally concerned about the potential for the Chinese Communist Party to spread propaganda on the app. The Times and The Wall Street Journal have reported that passed this bill in part because of unsubstantiated accusations that TikTok was unfairly promoting one side in the Israel-Hamas war.

Imagine if the government told Jeff Bezos that he had to sell The Washington Post because it was worried that he might push a particular agenda using his control of the newspaper. Or to use a digital analogy, what if the government told Elon Musk that he had to sell X, formerly Twitter, because it didn't like his content moderation of legal speech? Those scenarios clearly have a connection to First Amendment protections.

Ownership matters

Transferring TikTok's ownership from one company to another matters greatly for the purposes of First Amendment analysis.


Supreme Court Justice Elena Kagan observed during oral arguments in a case unrelated to TikTok's ownership that ownership can make a difference in an app. She noted that the sale of Twitter to Elon Musk changed the character of the app. Kagan said, “Twitter users one day woke up and found themselves to be X users and the content rules had changed and their feeds changed, and all of a sudden they were getting a different online newspaper, so to speak, in a metaphorical sense every morning.”

Indeed, The Washington Post found a rightward tilt after Twitter changed hands.

By forcing the sale of TikTok to an entity without ties to the Chinese Communist Party, Congress' intent with the law is to change the nature of the platform. That kind of government action implicates the core concerns that the First Amendment was designed to protect against: government interference in the speech of private parties.

U.S. Rep. Raja Krishnamoorthi, co-sponsor of the House bill on TikTok, pointed to another instance where the U.S. government ordered a Chinese company to sell a U.S. app. In 2019, the Committee on Foreign Investment in the United States ordered the new Chinese owners of Grindr to sell the dating app, which the Chinese owners did the year. In that case, the foreign owners could not assert First Amendment rights in the United States, given that they were outside the U.S., and thus no court considered this issue.


TikTok is First Amendment protection against the law forcing its sale or ban.

National security claims

The government hasn't disclosed to the public the national security concerns cited in the TikTok law. While such concerns, if accurate, might warrant some kind of intervention, some Americans are likely to decline to take claims of national security urgency on good faith. To address skepticism of secret government power, particularly when it involves speech rights, the government arguably needs to present its claims.

U.S. Sens. Richard Blumenthal and Marsha Blackburn, both of whom supported the TikTok law and have seen the government's secret evidence, called for the declassification of that information. We believe that's a vital step for the public to properly consider the government's claim that a ban is warranted in this instance. In any case, the courts will ultimately weigh the secret evidence in determining whether the government's national security concerns justified this intrusion upon speech.

What seems likely to happen, absent judicial invalidation or legislative repeal of the law, is a world in which TikTok cannot effectively operate in the United States in a year's time, with mobile app stores unable to push out updates to the software and Oracle Corp. unable to continue hosting the app and its U.S. user data on its servers. TikTok could go dark on Jan. 19, 2025, in the United States.The Conversation

Anupam Chander, Professor of Law and Technology, Georgetown University and Gautam Hans, Associate Clinical Professor of Law, Cornell University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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AI chatbots are intruding into online communities where people are trying to connect with other humans



theconversation.com – Casey Fiesler, Associate Professor of Information Science, of Colorado Boulder – 2024-05-20 07:27:05
AI chatbots are butting into human spaces.
gmast3r/iStock via Getty Images

Casey Fiesler, University of Colorado Boulder

A parent asked a question in a private Facebook group in April 2024: Does anyone with a child who is both gifted and disabled have any experience with New York City ? The parent received a seemingly helpful answer that laid out some characteristics of a specific school, beginning with the context that “I have a child who is also 2e,” meaning twice exceptional.

On a Facebook group for swapping unwanted items near Boston, a user looking for specific items received an offer of a “gently used” Canon camera and an “almost-new portable conditioning unit that I never ended up using.”

Both of these responses were lies. That child does not exist and neither do the camera or air conditioner. The answers came from an artificial intelligence chatbot.


According to a Meta help page, Meta AI will respond to a post in a group if someone explicitly tags it or if someone “asks a question in a post and no one responds within an hour.” The feature is not yet available in all regions or for all groups, according to the page. For groups where it is available, “admins can turn it off and back on at any time.”

Meta AI has also been integrated into search features on Facebook and Instagram, and users cannot turn it off.

As a researcher who studies both online communities and AI ethics, I find the idea of uninvited chatbots answering questions in Facebook groups to be dystopian for a number of reasons, starting with the fact that online communities are for people.

Human connections

In 1993, Howard Rheingold published the book “The Virtual Community: Homesteading on the Electronic Frontier” about the WELL, an early and culturally significant online community. The first chapter opens with a parenting question: What to do about a “blood-bloated thing sucking on our baby's scalp.”


Rheingold received an answer from someone with firsthand knowledge of dealing with ticks and had resolved the problem before receiving a callback from the pediatrician's office. Of this experience, he wrote, “What amazed me wasn't just the speed with which we obtained precisely the information we needed to know, right when we needed to know it. It was also the immense inner sense of security that comes with discovering that real people – most of them , some of them nurses, , and midwives – are available, around the clock, if you need them.”

This “real people” aspect of online communities continues to be critical today. Imagine why you might pose a question to a Facebook group rather than a search engine: because you want an answer from someone with real, lived experience or you want the human response that your question might elicit – sympathy, outrage, commiseration – or both.

Decades of research suggests that the human component of online communities is what makes them so valuable for both information-seeking and social . For example, fathers who might otherwise feel uncomfortable asking for parenting advice have found a haven in private online spaces just for dads. LGBTQ+ youth often join online communities to safely find critical resources while reducing feelings of isolation. Mental support forums provide young people with belonging and validation in addition to advice and social support.

Online communities are well-documented places of support for LGBTQ+ people.

In addition to similar findings in my own lab related to LGBTQ+ participants in online communities, as well as Black Twitter, two more recent studies, not yet peer-reviewed, have emphasized the importance of the human aspects of information-seeking in online communities.


One, led by PhD student Blakeley Payne, focuses on fat people's experiences online. Many of our participants found a lifeline in access to an audience and community with similar experiences as they sought and shared information about topics such as navigating hostile healthcare , finding clothing and dealing with cultural biases and stereotypes.

Another, led by Ph.D student Faye Kollig, found that people who share content online about their chronic illnesses are motivated by the sense of community that comes with shared experiences, as well as the humanizing aspects of connecting with others to both seek and provide support and information.

Faux people

The most important benefits of these online spaces as described by our participants could be drastically undermined by responses coming from chatbots instead of people.

As a type 1 diabetic, I follow a number of related Facebook groups that are frequented by many parents newly navigating the challenges of caring for a young child with diabetes. Questions are frequent: “What does this mean?” “How should I handle this?” “What are your experiences with this?” Answers come from firsthand experience, but they also typically come with compassion: “This is hard.” “You're doing your best.” And of course: “We've all been there.”


A response from a chatbot to speak from the lived experience of caring for a diabetic child, offering empathy, would not only be inappropriate, but it would be borderline cruel.

However, it makes complete sense that these are the types of responses that a chatbot would offer. Large language models, simplistically, function more similarly to autocomplete than they do to search engines. For a model trained on the millions and millions of posts and comments in Facebook groups, the “autocomplete” answer to a question in a support community is definitely one that invokes personal experience and offers empathy – just as the “autocomplete” answer in a Buy Nothing Facebook group might be to offer someone a gently used camera.

Meta has rolled out an AI assistant across its social and messaging apps.

Keeping chatbots in their lanes

This isn't to suggest that chatbots aren't useful for anything – they may even be quite useful in some online communities, in some contexts. The problem is that in the midst of the current generative AI rush, there is a tendency to think that chatbots can and should do everything.

There are plenty of downsides to using large language models as information retrieval systems, and these downsides point to inappropriate contexts for their use. One downside is when incorrect information could be dangerous: an eating disorder helpline or legal advice for small businesses, for example.


Research is pointing to important considerations in how and when to design and deploy chatbots. For example, one recently published paper at a large human-computer interaction conference found that though LGBTQ+ individuals lacking social support were sometimes turning to chatbots for help with mental health needs, those chatbots frequently fell short in grasping the nuance of LGBTQ+-specific challenges.

Another found that though a group of autistic participants found value in interacting with a chatbot for social communication advice, that chatbot was also dispensing questionable advice. And yet another found that though a chatbot was helpful as a preconsultation tool in a health context, patients sometimes found expressions of empathy to be insincere or offensive.

Responsible AI development and deployment means not only auditing for issues such as bias and misinformation, but also taking the time to understand in which contexts AI is appropriate and desirable for the humans who will be interacting with them. Right now, many companies are wielding generative AI as a hammer, and as a result, everything looks like a nail.

Many contexts, such as online support communities, are best left to humans.The Conversation

Casey Fiesler, Associate Professor of Information Science, University of Colorado Boulder


This article is republished from The Conversation under a Creative Commons license. Read the original article.

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