Podcast Episode

Part 1: Bridges and Synchrony 

Amna: On a windy Thursday morning in 1940, just 4 months after the legendary Tacoma narrows bridge was opened to the public, people started noticing that it had started swaying pretty visibly across its length. This bridge standing as one of the longest bridges in the world, was the pride and joy of America. As the swaying became more dramatic, officials blocked all oncoming traffic - just in time - before a cable buckled under - and the bridge literally started rotating across its axis. If you’ve seen the videos, Im sure you’ll agree that it all looks so surreal that its hard to believe its not some sort of CGI.  

At 11 am, one of the longest, most beautiful bridges in the world collapsed into the water below. It was a moment like the fall of THEE titanic that went down in textbooks as one of the most colossal engineering failures in history. Fast forward 60 years - engineers thought they had figured it all out and the millenium bridge was built in London, UK. But soon after its opening it seems to be having the same problem.  

So what exactly was going on here? 

This is Tethered Minds by Amna Hyder. In this episode we are going to be talking about the science of synchrony. This doesn’t just impact bridges, but it plays a huge role in our daily lives in ways we DONT even understand. There is a REMARKABLE beauty to synchrony. Our brains wouldn't exist if it weren't for millions of neurons firing in step. Our hearts wouldn't pump if it weren't for a coordinated action of million of your little heart cells. Synchronizing with with others has allowed us accomplish everything we have so far. But, we’re going to see what happens when synchrony goes wrong. How, in the wake of this new era, it is increasingly tearing us apart. AND, how it can break bridges.  

Amna: When you are looking at bridges, there is no better place to look than London. London is famous for them, and that’s why, at the start of a new millennium, the country decided to fund a new bridge. One that was meant to be the icon of a century. 

The millennium bridge was the stunning collaboration between prestigious architects, artists and engineers and it was opened to the public on June 10th, 2000. But it really made headlines around the world when it was closed just 2 days later 

Dr. Abrams: I first heard about this problem from my graduate advisor Steve strogatz. What happened was a mystery no one really understood why this happened bridges were thought to have been well understood
 

Amna: That is Dr. Daniel Abrams, an applied mathematician who not only who helped crack the case about what happened to the millennium bridge, but also how the mystery behind it could surprisingly explain some of the most important patterns in our social world 

Dr. Abrams: So the engineering firm did some experiments where they had people walk back and forth between two cones on the bridge in groups of 10. They would start with ten people they'd be measuring carefully the acceleration of the bridge with instruments and then they try 20 people and they try 30 people and they do watching acceleration it's nothing serious  

Amna:  40 people, 50 people, 100 - still no movement. But when they went from 150 people to 160, there was a sudden switch.

Dr. Abrams : they saw went from stable to unstable and started oscillating.

Amna:  Ok so Im going to give a disclaimer here, this particular episode starts with a slightly unconventional approach to understanding social psychology; some very cool physics. If that isn’t your thing, please bear with me, we wont use any numbers, equations or complicated words, and I promise, that by the end, my favourite corner of physics might be yours too.

Amna:  So theres a couple basic things we need to know. The first, is that absolutely nothing in the universe is still. Every single thing, even the things, we think must certainly be still, are wiggling, just a tiny bit. 

Dr. Abrams likens this movement to the more obvious movement of a grandfather clock.

Dr. Abrams: It has a natural speed a natural time it takes to go left right and back to the left if it’s swinging and that’s how grandfather clocks keep time that’s how traditionally all pendulum clocks keep time because that’s such a regular predictable pattern of oscillation with a very accurate timing 

Amna:  It turns out that the same way a pendulum on a grandfather clock moves at its own consistent beat, a bridge is also always vibrating at its own microscopic consistent beat. But to understand how this microscopic beat became dangerously powerful, Dr. Abrams took this knowledge and he coupled it with something else. Something we’ve all observed in a child’s playground.

Dr. Abrams: Say you're pushing a child on a swing if you try to push them when they're not there, when they're not all the way back if you're standing behind them you're not going to be pushing empty air, you're not going to give them energy they're not gonna get going but if you push with the right timing every time they reach that sort of limit of their swing in the back you're gonna pump energy

Amna:  and that beat is what scientists call a resonance frequency

Dr. Abrams: It has a specific timing that's associated with getting energy into the system and every structure has a resonant frequency or multiple resonant frequencies that will allow you to add energy to the system and in the case of a bridge perhaps destroy it if too much energy goes into it

Amna:  I dont know if youve ever pushed an adult on a swing before, but its pretty easy. You dont have to apply a lot of force to push someone pretty high, but you have to apply that force to the right beat. And the same is true for bridges. 

Amna:   Like a swing, a bridge has a certain frequency that it likes to move at

Dr. Abrams: When you design a bridge you can predict what these frequencies are based on the length of the span and the stiffness of the material that the deck is made from and the tension of the support wires.

Amna:  To get a bridge to move, you dont have to apply a lot of force, it just has to be applied at the right frequency. 

In fact that’s exactly what happened with the infamous collapse of the Tacoma Narrows. It had been made to withstand all kinds of forces. You could fill the bridge end to end with massive trucks filled with granite, and it wouldn’t budge, but what ultimately caused it to collapse was gusts of wind.

Dr. Abrams: So it didn't happen on that bridge when the wind speed was much higher than the day it collapsed. It it had been through much much higher wind days but it happened when the wind speed was just right to cause resonance with the bridge structures natural instability

Amna:  When wind blows, it often cycles around a bridge at some predictable speeds or frequencies. That fateful thursday in 1940, like every other day, the Tacoma narrows was wiggling at its own microscopic natural frequency. But at some point, the cycles of the wind synchronized with the frequency of the bridge. And the winds started pushing the bridge just like you might push someone on a swing, higher and higher until… “crash” 

After the Tacoma narrows collapsed, people started to design bridges so they would not be sensitive to gusts of wind. 

So thats why when the Millenim bridge in London started swaying, people started to wonder, could the bridge be synchronizing with something else? And thats where Dr. Abrams came in. He was intrigued by the odd behaviour of the people on the bridge that seemed to be unintentionally moving in sync. 

Dr. Abrams:  the key insight here that bridge engineers have had for years is that people walk typically about 2 foot falls every second

Amna:  up down up down, 2 beats per second

Dr. Abrams: and bridge engineers when they're designing bridges they know to avoid that frequency because if a big crowd goes over it you're probably going to get a lot of forcing at that frequency

Amna:  and when he says avoid he means...

Dr. Abrams: you can tune which frequencies they are most likely to respond to and to get excited by

Amna:  This has been well understood for years. It’s why soldiers have been told to break stride when they cross a bridge. So the bridge was already designed so that it wouldn’t be sensitive to 2 beats per second. But something that had never been considered before, and one that Dr. Abrams confirmed through his mathematical models, is that when people walk they not only push up and down, but they also push just a little bit, side to side. For every two up and downs (can play metronome 2Hz), there is one cycle side to side that our footsteps take (can play metronome 1 hz).

Dr. Abrams: and that

Amna:  1 beat per second

Dr. Abrams: it turns out was very close to the natural frequency of one of the spans of this bridge. Before that people did not think about this as a dangerous frequency for a bridge

Amna:  This was a small beat dangerous enough to break the bridge of a century. I want to stop for a moment just to appreciate this concept of resonance. You’d expect that if you want to get something to move, you have to put an equal amount of energy in. The whole is equal to the sum of its parts - that’s what our basic intuition tells us, and also how scientists and philosophers thought the world worked for so many years. Ultimately, it wasn’t that the bridge couldn’t handle the weight that was on it. It just couldn’t handle the beat of the footsteps. When things synchronize in just the right way, magic happens. And there’s a precise moment in which it does. 

When the bridge engineers experimented with people crossing the bridge, they didnt detect any movement when 50, 100, 150 people were on it. But when they got 160 people, suddenly the whole bridge started moving. 

Dr. Abrams: yeah that's the most surprising phenomena and one that's hard to see without math. In a lot of these systems you will you have is called a phase transition. We use that same description for explaining how water turns in to ice or turns into steam as a change in in its phase and mathematically the theory we developed shows a phase transition where you go from a bridge being nearly perfectly stable to suddenly having significant levels of oscillation and there's a critical transition there at some number of people at which that happens

Amna:  so it changes its phase it goes from this stable stationary state to this stable oscillating phase as you increase the number of people

Dr. Abrams:  why intuitively do phase transitions occur I've never heard a great intuitive explanation but this is a widespread phenomenon in nature throughout physics chemistry and engineering that phase transitions can occur in complex systems

Amna:  If you are a harry potter fan, you might remember the living portrait of the fat lady who tried to break a glass with her voice. While she had to cheat a little, there are people who can do this. 

How? Well like everything else in the universe, a glass also vibrates at a certain frequency (sound of spoon hitting glass). When you make a sound that matches with that frequency, the glass starts vibrating more and more, until it hits some key transition point and shatters.

But its not all just things breaking, synchrony can be quite beautiful too.

Dr. Abrams: So one thing I have an interest in at the moment I'm excited about is fireflies there are these things called synchronous fireflies

Amna:  And like normal fireflies, they start with random firing, each firefly chaotically flashing on its own. But suddenly there’s this stunning phase transition

Dr. Abrams: And they will synchronize their flashes over a whole bush or even a whole riverbank will be blinking on and off flashing in unison.

Amna:  The symphony of light creates such a spectacular display that fisherman can use it to guide their way back to their home. And its so surreal that in the 1500s, when the explorer St Francis drake returned ho me with tales of these synchronous fireflies, no one believed him. And even up until the 20th century there were scientists that were convinced that the flashing was some sort of optical illusion. Not much has been known about them, until recently.

Dr. Abrams: it's one of these charismatic species and if you care about conservation it's a great ambassador species that that you don't want to see disappear, and I'm part of a project that is going to go do some new recordings of the fireflies in their home base.

Amna:  Wow, so you’ll see hundreds or thousands of these fireflies flashing in perfect synchrony. Do you think theres some great firefly leader out there that is setting a rhythm for everyone else or does this synchrony just emerge on its own?

Dr. Abrams: This is exactly what we want to know the answer to so I don't know. You may or may not have have experienced this where people can start clapping In Sync right you can get a beat without a leader, you don't need someone to set the tone for for clapping if everybody just decided we're going to clap and you start with kind of kafani and then within a few seconds really a few claps everyone gets into a rhythm. That's emergent --- clapping sound -- so without a leader it could definitely happen but it could be happening with a leader maybe there's some unknown leader that we don't understand

Amna:  Ok Id lve love to use that thread of human clapping to conversation about synchrony between humans. Can you talk a bit about that?

Dr. Abrams: So I would call this social synchrony, I think what you're asking about how do people not within your body but across multiple people agree on something and I think these problems of social synchrony exist across many timescales, theres this timescale of human evolution

Amna:  And in one problem Dr. Abrams decided to look over hundreds of thousands of years to answer a question of human handedness. And he asked...

Dr. Abrams: how is it that about 90% of people are left are right-handed and about 10% left handed. In my mind it's a synchrony problem so it seems like we've reached an equilibrium where we've all kind of agreed to be right-handed in an evolutionary sense but yet some small fraction of left handers persist

Amna:  ok so I’m trying to guess where you might be going here. If sharing the same handedness served an evolutionary purpose, like allowing us to share tools? 

Dr. Abrams: I think I think you hit the nail on the head and figuratively and appropriately by saying that talking about sharing tools I think so I think that’s a key aspect of why we have handedness at least at a group level in humans

Amna:  So do you see differences between different or populations in the fraction of right handed people?

Dr. Abrams: There is some evidence that the fraction left hand is higher in societies in hunter gatherers societies where violence rates of interpersonal violence were higher, the name this goes by is the fighting hypothesis, the idea that left handers have an advantage when fighting but in most other situations they’re at a disadvantage because they can’t effectively share tools

Amna:  Right, so the idea being that fighters would do better if their handedness was different. Have you done any studies to explore this?

Dr. Abrams: so when I worked on this we looked at sports as a model system because obviously you cant do experiments with evolution but you see drastic overrepresentation of lefties in many sports where they have this sort of fighting advantage this surprise advantage, because they've practiced the left-hander has practiced a lot against right handers in their career but right handers don't get to practice against left handers much so that gives them in general a big a big edge

Amna:  Archeological evidence from bone density and types of tools shows that 10% of humans have been right handed for about 500,000 years but at one point that wasn't the case. 

Dr. Abrams: In many animal species it's about a 5050 split on lefties and righties

Amna:  Like other animals, its likely that at some point, our predecessors were equally likely to be left or right handed

Dr. Abrams: During evolutionary history there was a selection for right handers and times in situations where cooperation was important and in times when competition or physical confrontation married then lefties have an advantage to this 10% I think represents a balance between those two

Amna:  You can make a mathematical model also in the spirit of synchrony and show that the symmetric solution would be stable when you don't have too much cooperation when you have a lot of cooperation it becomes unstable branch off into one into a different solution where by again a type of phase transition where you end up with the majority one handed

Amna:  But its not just handedness to share tools, our brains have an innate blueprint for social synchrony. This structure is called the mirror neuron system. I studied this myself in grad school by scanning two peoples brains at the same time while they interacted with each other. It might sound like science fiction, but this is real science. 

Theres been multiple studies where they do this. Take two people and scan their brains simultaneously while they talk to each other or play a game. And whats been shown over and over is that when people cooperate, each persons mirror neuron systems start to fire in sync. This system lays the ground work for all sorts of human synchrony. So I asked Dr. Abrams about what this human synchrony could look like

Dr. Abrams: Sure, I'll give a couple of examples so there are ways in which human synchronized like on the Millennium bridge people synchronize their footfalls without you know consciously trying to do so. When people walk it's mostly unconscious activity but you tend to synchronize your speed also with people walking nearby on a sidewalk for example

Amna:  But then theres another level of synchrony and is where an entire population starts to adopt the same thoughts.

Dr. Abrams: And so this has goes by different names in social sciences: sometimes it's called the consensus problem, how do people reach consensus. You can think about consensus in like an opinion on a political issue for example but it can also be consensus on like a language spoken in a region like why do the native people of this particular area of this country speak how did they end up speaking the same language

Amna:  Think about it, languages change over time. New words are added to the dictionary nearly everyday and definitions change of old ones. Definitions change when they are used differently by enough people

News Clip

Amna: And New words get added to a dictionary when enough people start using them. 

News Clip: “so now we official, we are in the dictionary”

Amna:  There is no appointed leader that decides how language will change over time. It emerges on its own by mass consensus over an entire population. 

We see synchrony everywhere. Whether its people synchronizing on the words we use, or even the synchronous movement of schools of fish.

Dr. Abrams: All these things can be seen as synchrony problems where you may or may not want synchrony, you may want consensus, you may not, but understanding how it emerges is the real challenge of the day of the day particularly in terms of polarizaiton which is becoming a real problem in the US i think

Amna:  If you arent impressed by any of this so far, it might be because synchrony is so deeply embedded in our daily lives that its hard to appreciate its beauty. But if take a class in physics, one of the first things you are taught is that the universe tends towards disorder – its known as the third law of thermodynamics. 

When you drop a piece of glass and it shatters, you cant put it back together. Physical systems don’t naturally go from chaos to order. This is why synchrony is so beautiful. In a universe that becomes more and more disordered, there are so many examples of where things go spontaneously from chaos to an ordered synchrony. And if we want more order, we need to understand how this works. 

Right after the break, we will talk about how this concept of synchrony can help us make sense of and potentially fix the political polarization that we are seeing all around the world.

Dr. Abrams: I think there is a lot of overlap between the math that is used to describe synchrony and the math that is used to describe fads and social phenomenon and something going viral.

Amna: Welcome back. We are exploring how groupthink comes about and the tipping point that sets it off. Just like the emergence of synchronized clapping (clap sound), there is a transition point for when something goes viral. Physicists or mathematicians would typically call something a tipping point for a system the input is slowly changed and not much changes in the output until you pass the tipping point. The renowned author Malcolm Gladwell, who wrote an entire book about just this, described it in an interview.

Malcolm Gladwell: I think the tipping point is the word that comes from studying functions is to describe that moment in the epidemic when it explodes and there were number of critical mass and if you look at every epidemic there is always that moment when the curve suddenly shoots up very sharply and dramatically, and so the response becomes disproportionate to the change in input and so understanding how you can get to the tipping point is the critical question when you're looking at something that's contagious

Amna: Gladwell was particularly interested not in how viruses spread but how ideas and actions could spread between humans.

Malcolm Gladwell: you know I talk in the book about the word yawn if I say the word yawn long enough you will start yawning and exactly people watching the show will start yawning that's an incredibly contagious word 

Amna: According to Gladwell are a few factors that influence whether or not something becomes popular. The first is called the stickiness factor. And this represents the ability of something to capture our attention and be passed on. 

baby shark doo doo do do do doo 

Amna: We need to defer to some social psychology to understand what types of things are sticky so we spoke to the author and social psychologist Dr. Dominic Packer. He shared that when it comes to social media, we are drowned in information throughout the day. He has spent a lot of time looking into what types of things capture our attention in this flood. 

Dr. Dominic Packer: Right, yes that's right so we lots of research is ongoing in this regard but we certainly know a few things so for example there's a statistic we cite which is that on average it seems that smartphone users scroll through social media on their screens or something like 600 times a day

Amna:  so 600 scrolls

Dr. Dominic Packer: and if you assume each screen is on average about 6 inches tall

Amna: what that means is 300 feet worth of information a day

Dr. Dominic Packer: which translates to the height of the Statue of Liberty which is kind of large right?

Amna: Its huge. It literally means that every single day, on average, we scroll, inch by inch, all the way up height of the statue of liberty

Dr. Dominic Packer: and so then you have to ask alright well in this vast slew of stream of sort of onslaught of information what do we pay attention to?

Amna: And so Dr. Packer’s co-author decided to look at over half a million tweets with certain key words

Dr. Dominic Packer: and what they're finding, which is super interesting, is that there's a certain class of words called moral emotional words which tend to attract attention very quickly, but also be more likely to be shared, and spread virally.

Amna: in other words they have a high stickiness factor

Dr. Dominic Packer: And moral emotional words are not just emotional words like happy sad and they're not just moral words like good and bad they are the combination of both their words like disgusting hate * news clip*  terrible the sort of things that have this moralizing component like they're judging people as often bad but it could be good in some cases but also have this really strong viscerally emotional response like that is absolute disgusting and it turns out that tweets or Facebook posts that contain more of those words tend to be more likely to spread through networks.

Amna: Each moral emotional word increases the chances of a tweet being shared by a whopping 17%. These words are sticky

Dr. Dominic Packer: Which of course you could imagine isn't necessarily the best thing, right, that you get these feedback loops where people who want messages to go viral are probably not consciously but they're sort of learned overtime that if you use more of this sort of language make more likely to spread and so they end up using more of that language, which means that more of those sorts of messages do indeed go viral. And you get the spread of toxicity throughout social networks.

Amna: In fact, almost to prove their point, one of the student’s in this lab posted a tweet made up entirely of these moral emotional words. 

Narrator: “attack, bad, blame, care, destroy, fight, hate, kill, murder, peace, safe, shame, terrorism, war and rob”

Amna: And it was retweeted almost immediately over 600 times.

Dr. Dominic Packer: Whats worse? Negative words are more sticky than positive ones. One study looking at tweets and facebook posts by US congress members had SHOCKING results. They found that negative language increased the number of shares by 45% for each word, while each positive word actually decreased the number of shares by 2-5%.

Amna: But its not just the stickiness alone that allows you to predict whether or not something will go viral. It matters where and when it happens. Malcolm gladwell calls this the power of context. What goes viral in one place might not in another, and the groups we find ourselves in affect this a lot

Dr. Dominic Packer: The other thing they found is that most of that spreading occurs within the ingroups, that is when they analyzed how much things get for example by Democrats and Republicans what they found is that Democrats tend to retweet other Democrats and Republicans tend to retweet other Republicans and you don't get a whole lot of cross fertilization in any sort of productive way.

Amna: This means we are stuck in echo chambers, with our own voices being shouted back at us synchronizing with that of our group members. And as for type of content we see? Dr. Packer told us about the stickiness of moral emotional words, and negative language. This allows social media to become the perfect incubator for hoaxes, because to the algorithm all that matters is how much attention something gets, not how true it may be.

Dr. Dominic Packer: Yeah so Jay, especially in his lab, have done some studies looking at people's receptivity to sort of inaccurate information for example in headlines headline news and the general pattern is that people again seem to be more I should say less skeptical of information that reflects positively on their group and reflects negatively on an outgroup especially in a competitive context like politics

Amna: In the 2016 US elections, news circulated that the pope endorsed Trump, but the exact opposite news, that the pope had actually endorsed, was also being shared

Amna: You could make the argument that perhaps we believe these things to be true because its all we see in our echo chambers. But whats worse, when we are exposed to information that attempts to correct these beliefs from outgroup sources, that can actually cause people to retreat more firmly into their hateful false beliefs. Dr. Abrams has used this phenomenon in his own mathematical models.

Dr. Abrams:  people have mostly an inclination towards consensus you might tend to change your view to be more in alignment with the opinion you just heard expressed but maybe if it came from the opposing party you might not change your opinion as much or you might it might even backfire if the information you get from an outgroup source is so different from what you currently believe it might cause you to move your political viewpoint in the opposite direction so this is called a backfire effect and it's been recently documented in some experiments via Twitter

Amna:  Moral emotional words are sticky, they go viral even when the content is a lie and trying to rectify it by exposing people to other sources often causes them to retreat even further into their groups. We end up in echo chambers synchronizing with our own groups and moving further away from others that it’s hard to even start to understand the views of those outside our groups.

Dr. Abrams:  I think both those things are happening that not only are we more likely to be repelled by opinions we encounter on Facebook or other social media the opinions that we encounter are not representative of the population as a whole but they're already more extreme than the typical person odds and so it it leads to this situation of echo chambers and feedback of negative opinions that one for each person finds may be needlessly outrageous or repulsive

Amna:  In the real world, to go viral information would have to travel largely through word of mouth, but on social media virality is engineered. Algorithms pay close attention to content that gets engagement give it a boost.

Dr. Abrams:  Things spread that are likely to stick, things go viral when they reach a tipping point and I think that's one of the big problems with social media is that negativity and conflict are so much more likely to spread

Amna:  So this social psychology is very cool but Dr. Abrams, how do you as a mathematician incorporate this social science in your own work?

Dr. Abrams:  we look for fundamental mathematical models that seem to capture key aspects of human behaviour

Amna:  and whats your goal with these models?

Dr. Abrams:  so I think the mathematicians can be useful in terms of understanding and quantifying these fundamental responses, but then it moves into other territory of like how do you address this? you can try out once you have a mathematical model you can try out theoretical solutions like look pretty fact deemphasizing posts they're disproportionately polarizing you could imagine emphasizing only things that engage both in Group and outgroup in similar ways

Amna:  This is the space where policy makers, social psychologists and mathematicians come together.

Dr. Abrams:  whatever the specific policy is I'm not sure what the right policy is and whether it would be conceivable that that it could be implemented but if you have a mathematical model that at least is is captures some fundamental aspects of human behaviour that gives you the opportunity to test in the computer what the result of different policies would be and it motivates trying out some policies over others

Amna:  Everyday, researchers like Dr. Abrams and Dr. Packer are working on trying to figure this out to create a more positive outcome from this innate human impulse to synchronize. There is a delicate dance to the synchrony between us and so much is unknown about the tipping point that sets it off. For better or worse, Just like the synchrony of our footsteps on a bridge, our collective power is greater than each of us alone. We can let that let that destroy us, or we can harness it to our advantage. But Its only in understanding how it happens that we can hope to steer the ship

Amna:  Thats all for today with tethered Minds by Amna Hyder. btw I just started this podcast so if you like what you hear please share and subscribe! 

Next month we will be talking about everything nostalgia from its bittersweet history and its fascinating psychology. As we deal COVID, climate change and social distress, these days uncertainty feels like the only certainty, and many argue nostalgia is the emotional pacifier that many of us are falling back on. The renowned researcher Dr. Clay Routledge will walk us through how we can use nostalgia to better our physical health and emotional well-being. And Dr. Anna Stefaniak will share the fundamentally social nature of nostalgia and how many politicians use it as a political tool to get support for their platforms.