How Physics Could Make Big Crowds Safer

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/shortwavesurvey http://npr.org/shortwavesurvey Listen 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 http://plus.npr.org/shortwave. See pcm.adswizz.com https://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 https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:16Regina Barber?

  Hey, ShortWavers. Before we get started, quick little favor to ask. Can you help us shape the future of Short Wave by completing a short anonymous survey? It's a chance for you to tell us about what you like and don't and how we can serve you better. It's an awesome responsibility, but I trust you. And we want to hear from everyone, whether you're a day one or brand new listener. Just go to npr.org/shortwavessurvey. We'll also put a link in our show notes. Thank you. OK, on to our show.

• 0:45Speaker 00

  You're listening to Short Wave from NPR.

• 0:51Regina Barber?

  Hey, ShortWavers. Regina Barber here.

• 0:53Emily Kwong?

  And Emily Kwong.

• 0:54Regina Barber?

  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.

• 1:05Speaker 03

  Thank you. Hi, guys.

• 1:07Emily Kwong?

  Hi, Elsa.

• 1:08Speaker 03

  So give me my science presence this week. What do you have for me today?

• 1:12Regina Barber?

  We got you. OK, so we're going to talk about how the physics of fluids can help crowd control.

• 1:18Emily Kwong?

  How our mood may be better in the morning.

• 1:21Regina Barber?

  And a fossil that might shed light on the early ancestors of modern birds.

• 1:25Speaker 03

  OK, I'm a little bit skeptical about the second one, but very excited to hear what you guys have to say.

• 1:30Regina Barber?

  I'm a morning person. You might hate me now.

• 1:33Speaker 03

  Kind of do.

• 1:34Regina Barber?

  All that on this episode of Short Wave, the science podcast from NPR.

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• 3:09Speaker 03

  All right, Gina, I want to start with how crowds of people can act like fluids.

• 3:14Regina Barber?

  Yes. I mean, this is physics, so I love it. Okay, so this is really clear in this video of a crowd, around 5,000 people during the San Fermin Festival in Pamplona, Spain. And this is a gathering the day before the Running the Bulls. Okay, do you want to see?

• 3:29Speaker 03

  Yeah.

• 3:29Regina Barber?

  Okay, check it out.

• 3:32Speaker 03

  Whoa, it's like the crowds undulating.

• 3:35Regina Barber?

  Yeah, yeah.

• 3:36Speaker 03

  Like red water. They're all dressed in red or they're waving red things.

• 3:39Regina Barber?

  Yeah, they're waving red handkerchiefs. And this is a video from a rooftop. And you can 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.

• 3:53Speaker 03

  Which sounds kind of unsafe, looking at this.

• 3:57Emily Kwong?

  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 Astroworld 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?

• 4:15Speaker 06

  Dense crowds by themselves are not dangerous. So what's very dangerous when you're in a dense crowd is to be close to rigid walls. You want to be in the bulk. Do not go to the boundaries. Stay away from the bulk.

• 4:31Speaker 03

  Stay in the bulk. Okay, what does that mean, Regina?

• 4:34Regina Barber?

  Yeah, so this is some like 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.

• 4:56Speaker 03

  And what did they find?

• 4:57Emily Kwong?

  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...

• 5:13Speaker 06

  And because these spontaneous motions are periodic in time, they are very easy to detect. And they are very easy to detect very early on, before they become dangerous.

• 5:22Regina Barber?

  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.

• 5:36Speaker 03

  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.

• 5:48Regina Barber?

  That's me.

• 5:50Speaker 03

  And now you're telling me that science says I should feel better in the morning?

• 5:54Emily Kwong?

  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 1 million observations. And those trends were published in the journal BMJ Mental Health this week.

• 6:16Speaker 03

  Okay, and what trends did they find?

• 6:18Emily Kwong?

  Generally speaking, people's mental health and well-being were better in the summer than in the winter.

• 6:23Speaker 03

  Okay.

• 6:24Emily Kwong?

  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.

• 6:44Speaker 03

  And then when did they report the lowest levels on average?

• 6:47Regina Barber?

  Elsa, it was midnight.

• 6:49Speaker 03

  What? Midnight is when I feel most alive, people.

• 6:52Regina Barber?

  Not me, not me.

• 6:54Emily Kwong?

  Yeah, you're totally an outlier for the study. Lead author Fei Fei Bu says their model acknowledges that people are not all the same.

• 7:00Speaker 03

  Surprise, surprise.

• 7:01Speaker 07

  What we focus on mostly in the study is a group trend. It's not a personal rulebook.

• 7:10Regina Barber?

  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 hours somebody is awake. But still, 50,000 people is quite a large sample size.

• 7:30Speaker 03

  I guess so, but did the scientists say why mornings feel brighter to some people out there?

• 7:37Emily Kwong?

  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." That's 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.

• 8:12Speaker 03

  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?

• 8:22Emily Kwong?

  Nailed it.

• 8:23Regina Barber?

  Yep.

• 8:23Speaker 03

  Nailed it. Okay, Gina, set the scene for us like a movie director. Paint us a picture.

• 8:28Regina Barber?

  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 billion years ago.

• 8:43Emily Kwong?

  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.

• 9:06Speaker 03

  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?

• 9:15Emily Kwong?

  OK, 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, Wegavus, used its legs to dive underwater and swim to catch fish. It had a very strong jaw, probably to quickly snap its beak closed while swimming underwater. And the study authors say the skull helps confirm a previous hypothesis that Wegavus was closely related to ducks and geese.

• 9:40Regina Barber?

  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 the 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.

• 10:01Speaker 03

  OK, well, all the controversy aside, why do we even care about a skull from 66 million years ago?

• 10:06Emily Kwong?

  Fair question. Well, Chris Torres, one of the study authors, says the 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.

• 10:36Speaker 03

  Right, and history is there to make us, I guess, better prepared for today, yeah?

• 10:40Emily Kwong?

  I hope.

• 10:41Regina Barber?

  Yep. Elsa, it's always just a party to have you on. We love having you on.

• 10:45Speaker 03

  Oh, thank you so much for always inviting me.

• 10:48Emily Kwong?

  Come back anytime, Elsa.

• 10:49Speaker 03

  Oh, I will. Thank you, guys, so much.

• 10:55Regina Barber?

  You can hear more of Elsa Chang on Consider This, NPR's afternoon podcast about what the news means for you. Also, make sure you never miss a new Short Wave 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 Intagliata and our showrunner, Rebecca Ramirez.

• 11:15Emily Kwong?

  Tyler Jones checked the facts. Kwasi Lee was the audio engineer. I'm Emily Kwong.

• 11:20Regina Barber?

  And I'm Regina Barber. Thank you for listening to Short Wave, the science podcast from NPR.

• 11:42Speaker 05

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