Short Wave - How Physics Could Make Big Crowds Safer

Episode Date: February 7, 2025

What do large crowds of people and water have in common? They both act like fluids. When crowds cheer, sway and clump together, the movements look like ripples of water. Researchers hope insights from physics like this one could help officials and engineers create safer crowds at festivals.Help shape the future of Short Wave by taking our survey: npr.org/shortwavesurveyListen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

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You're listening to Shortwave from NPR. Hey, Short Wavers, Regina Barbara here. And Emily Kwong. With our biweekly science news roundup featuring the hosts of all things considered. And today we have one of our favorites, the fun, the full of energy, Elsa Chang. Thank you. Hi, guys. Hi, Elsa.

Give me my science presence this week. What do you have for me today? We got you. Okay. So we're going to talk about how the physical. of fluids can help crowd control. How our mood may be better in the morning. And a fossil that might shed light on the early ancestors of modern birds.

Okay. I'm a little bit skeptical about the second one, but very excited to hear what you guys have to say. I'm a morning person. You might hate me now. I kind of do. All that on this episode of Shorewave, the science podcast from NPR. All right, Gina, I want to start with how crowds of people can act like fluids. Yes.

I mean, this is physics, so I love it. So this is really clear in this video of a crowd around 5,000 people during the San Fermin Festival in Pampalona, Spain. And this is a gathering the day before the Running the Bulls. Okay, do you want to see? Yeah. Okay, check it out. Whoa, it's like the crowds undulating. Yeah, yeah.

Like red water. They're like all dressed in red or they're waving red things. Yeah, they're waving red handkerchiefs. And this is a video from a rooftop. And you can like really see that dense crowd. The density of this crowd is comparable to like, putting 900 people in a one-bedroom apartment. And they are, they're kind of moving like water.

Which sounds kind of unsafe looking at this. What's interesting about this gathering in Spain is that it's actually known to be very safe, even though there are so many people. But you may remember the Astro World Festival in Houston in 2021. There, 10 fans died in a crowd crush. So scientists want to understand what went wrong and how can we keep people safe in crowds? dense crowds by themselves are not dangerous. So what's very dangerous when you're in a dance crowd is to be close to rigid world.

You want to be in the bulk. Do not go to the boundaries. Stay away from the world. Stay in the bulk. Okay, what does that mean, Regina? Yeah, so this is some crowd management advice from Dennis Bartolo. He's a physicist at the Institutes of Advanced Education in Lyon, France. And he and his colleagues wanted to learn more about the factors that can turn crowds dangerous,

specifically those spontaneous movements of like dense crowds. So his team studied this Spanish festival crowd during four separate years. And what did they find? Yeah. So in the past they thought that crowd movements were random or chaotic. But Dennis and his team broke down the physics of the fluctuations and modeled the crowd. And for the first time, they found that dense crowds followed recurring predictable patterns, like clumping together and swaying.

And because the spontaneous motion are periodic in time, they are very easy to do. detect. And they are very easy to detect very early on before they become dangerous. They wrote about this in the journal Nature. So the hope is that authorities can monitor and then intervene if a crowd starts exhibiting this kind of like periodic behavior. Being able to monitor how a dense crowd moves brings us one step closer to figuring out what to do when it gets dangerous. Let's move on to the next topic, which I have a lot of skepticism about. Because, okay, I have never been a morning person. Like, I hate the morning. And people who are cheerful in the morning get on my nerves. That's me.

Now you're telling me that science says I should feel better in the morning? No, everyone does have a different circadian rhythm. This is actually just a study looking at 50,000 adults in the UK, which shows there are trends in mood, like a group average. This is from the University College London COVID-19 social study, which ran for two years, and contains nearly one million observations. And those trends were published in the journal BMJ Mental Health this week. Okay, and what trends did they find? Generally speaking, people's mental health and well-being were better in the summer than in the winter. Okay.

And participants reported their mental health and well-being were best early in the morning, meaning on average, the group reported the lowest depressive symptoms, anxiety, symptoms, and loneliness in the hours after waking. And during those hours, participants tended to report higher feelings of happiness, life satisfaction, and a sense of life being worthwhile. And when did they report the lowest-level? levels on average. Elsa, it was midnight. What? Midnight is when I feel most alive, people. Not me, not me. Yeah, you're totally an outlier for this study. Lead author, Faye Fouz, says their model acknowledges that people are not all the same. Surprise, surprise. What we focus on, mostly in the study, is a group trend. It's not a personal group book. And the group does not speak for everyone everywhere. All the participants were based in the UK. Most were women. Most were white.

Most had a college degree. The study did not account for shift workers. So the data is tied to time of day rather than the hour as somebody is awake. But still, 50,000 people is quite a large sample size. I guess so. But do the scientists say why mornings feel brighter to some people out there? Their study was more focusing on observations instead of like the cause. But other researchers have found similar trends. Frank A.J.L. Shear is a senior neuroscientist at Brigham and Women's Hospital and Professor at Harvard Medical School. He said our mood is known to worsen as we are awake longer. There's a lot of research about that. However, he and other scientists have found there's a second wind where mood improves in the afternoon and early evening. So clearly, the relationship between mood

and time of day is complicated. I think the big takeaway of this study, though, is that mental health and well-being changes throughout the day, throughout the week. It's just not a static thing. All right, for our next story, our third story, we're heading back tens of millions of years ago to the, okay, let me see if I say this right, Cretaceous period. Nailed it. Yep, nailed it. Okay, Gina, set the scene for us like a movie director, paint us a picture. Okay, so for this story, we're in the Antarctic Peninsula. Generally, it was more temperate than it is now, filled with lush, forested landscapes where dinosaurs roamed, at least until the mass extinction event, about 66 million years ago. And scientists don't know much about what kinds of animals might have made it through that mass extinction. For example, scientists predicted relatives of some of the earliest lineages of modern birds like ducks and geese were around, but they had very few complete records. However, a new paper out this week in nature details a big addition to the fossil records. It details the fossilized skull of one of the earliest known modern birds. Ah, okay, I'm so intrigued by this fossilized skull. Tell me about this bird.

And like, is it just like the birds I see today roaming around? Okay, this part is still controversial. Like, where should the fossil be placed on the evolutionary tree of life? We do know that this ancient bird, Vigavis, used its legs to dive underwater and swim to catch fish. It had a very strong jaw, probably to quickly snap its beak, close while swimming underwater. And the study authors say the skull helps confirm a previous hypothesis that Vagavis was closely related to ducks and geese. But some paleontologists say this is still up for debate. So Daniel Field is a paleontologist at the University of Cambridge.

He wasn't involved in this study. And he says the fossil appears to be close to the origin of modern birds. But we don't know enough to say that it is an early example of something like a duck. Daniel says in any case, the fossil adds important information to the debate. Okay. Well, all the controversy aside, why do we even care about a skull from 66 million years ago? Fair question. Well, Chris Torres, one of the study authors, says the whole.

hope is the fossil record helps shed light on these life-changing events in Earth's history. What we always hope for when we study the fossil record is to learn lessons about what causes life to change, to survive or to go extinct. And there is a biodiversity crisis right now. So fossils like this may help us understand what life was like in the moments before a mass extinction event and in the moments immediately after. Right. And history is there to make us, I guess, better prepared for today, yeah? I hope. Elsa, it's always just a party to have you on. We love having you on. Thank you so much for always inviting me.

Come back anytime, Elsa. Oh, I will. Thank you guys so much. You can hear more of Elsa Chang on Consider This and P.R.'s afternoon podcast about what the news means for you. Also, make sure you never miss a new shortwave episode by following us on whichever podcasting platform you're listening from. This episode was produced by Rachel Carlson and Jordan Marie Smith. It was edited by Christopher and Taliatta and our showrunner Rebecca Ramirez. Tyler Jones checked the facts.

Cui Cui Lee was the audio engineer. I'm Emily Kwong. And I'm Regina Barber. Thank you for listening to Shorewave, the science podcast from NPR.