6 ms·

Emergence of collective oscillations in human crowds

95 points by shalg 2y ago

nacho-daddy 2y ago
Crowds of a high enough density push people in orbital waves, with both clockwise and counterclockwise oscillations pulsing at 18 second intervals through the crowd. Monitoring these motions in realtime is possible and may help prevent crowd crush events. Also: At high densities crowds act like sticky springs, with the ground adding the sticky. 18 seconds before the next wave of people crushes you. 18 seconds to get out. 18 seconds could save your life.
- trimethylpurine 2y ago
  I like your summary. Thanks!
- diegoperini 2y ago
  Beautiful. Thank you.
- cmehdy 2y ago
  Two things that would deserve clarification (although outside of the scope of the research here) are: (1) When is it time to leave? At what threshold? Is it around an arm's length of free space between people? And (2) Where to go? Straight line towards an exit? Perpendicular to the crowd? Exactly against the flow? Along the flow but towards edges? Probably depends on a lot of parameters..
  - vxxzy 2y ago
    I don’t recall where, but for some reason I remember learning that if people start to bump into you too many times, that’s a warning shot to get out. It was something like “bumps per second”.
  - wongarsu 2y ago
    A naive application of fluid dynamics would suggest that the answer to 2 is to go perpendicular to the flow until you reach a wall, then go against the flow towards an exit. In the middle of a crowd/fluid your motion is determined by the humans/molecules around you. The closer you get to a wall, the fewer particles have an influence on you. Just make sure it's not a wall people are moving towards. Not sure if anyone has studied how well this holds up to humans. Human crowds have very fluid-like behavior, but of course they don't behave perfectly like a liquid in a pipe
    - xeonmc 2y ago
      > Human crowds have very fluid-like behavior, but of course they don't behave perfectly like a liquid in a pipe Hypothetically, how would the dynamic change if it were a crowd of cats instead?
      - thfuran 2y ago
        Non-cat fluids don't usually spontaneously draw knives and start cutting themselves apart.
    - alwa 2y ago
      Is there anything to the notion that you might prefer to be batted around in the “soft body” portion of the dense-crowd “fluid” rather than pinned between several tons of soft bodies in motion and a hard limit? You seem rather more crushable than an individual molecule might be… (edit: “crowd crush safety expert” Paul Wertheimer, who came to some notoriety through studying mosh pits from within them, apparently suggests—at least in situations where the crowd is moving toward a clear focal point—you’re right: he recommends the edges https://www.cnn.com/2021/11/13/us/how-to-stay-safe-at-concerts-cec/index.html https://www.cnn.com/2021/11/13/us/how-to-stay-safe-at-concer... That said I note that the authors of TFA draw a distinction between dense-crowd situations undergoing unidirectional flow and the steady, confined dense crowd whose behavior they describe.)
- metalman 2y ago
  .,.......except at a Greatfull Dead concert where this phenominon is called the "seeing the gears" or "have you seen the gears" nobody gets crushed, everybody gets....where they need to be plus up in the stands, are human waves of people, who are also bouncing a multitude of beach balls around, some of which are giant, some of which are not filled with air everybody steping to the groove.....except the spinners, who are another phenominon, the tapers huddled, but looking for any likely person at all to spell them bobby just played the grammys......
- samstave 2y ago
  Id bet that the 18 seconds is related to the amount of time between when people naturally shift on their feet/comfort pocket... Meaning that, if you notice the frequency by which people shift their weight and move -- its likely in that window, assuming other externalities (bathroom, heat, thirst, anger, etc -- the physiological cycle of body comfort may be in that area of 18 secs)
- patcon 2y ago
  Of note: If that 18 second rule became known to a significant number of people, the dynamic will change
- alwa 2y ago
  I read it kind of quickly, but didn’t their analysis suggest that the 18s period in question may have been specific to the Plaza Consistorial—that is, that the specific oscillation period may depend on the size (and possibly shape) of the confinement area? > To address the role of confinement, we perform an additional series of measurements after the festival opening, when a security team splits the crowd into two halves (Fig. 3e and Supplementary Video 4). We find that the two decoupled crowds still oscillate but at a higher frequency. We measure the shortest dimension of the crowds before and after the festival opening, and the extent of the region of space where the 2010 Love Parade crowd featured chiral oscillations (Methods). Figure 3h shows that the velocity spectra of these markedly different crowds peak at the same value when rescaling the frequency w by the inverse of the confinement length L. This result strongly suggests that the period of the emergent oscillations depends on confinement, and is not an intrinsic 'material' property.
- m463 2y ago
  I wonder if we couldn't have the equivalent of the water barrels near the start of guard rails, but for crowds? Maybe giant inflated or crushable areas around an exit that could take up slack? maybe tie the crush event with something else, like opening extra doors, turning on lighted warning signs or illuminating exits?
  - lifeformed 2y ago
    Doors with crash bars are kind of that. If there's too many people, they'll push up against them and force them open.
deleted 2y ago
[deleted]
qwertox 2y ago
The article contains a link to a YouTube video of the Loveparade 2010. It's pretty long and only at the end the oscillations are very noticeable (18:33 [0]). 21 people died and at least 652 were in part seriously harmed. [0] https://youtu.be/QpzISdBE3dA?t=1113 https://youtu.be/QpzISdBE3dA?t=1113
kanavs 2y ago
Interesting work! It is interesting how a lot of the models in physics and outside of it comes down to variations of harmonic oscillators (in this case macroscopic chiral oscillators). I am curious is the chirality gets imposed by the location and the architecture. Another interesting bit to explore would be how the agency (in my head agency is loosely defined as the number of possible actions you can take) of each individual gets contained as the crowd gets dense. If there is a way to define agency mathematically, it would be interesting to look at the correlation between agency and crowd density (my guess is inverse correlation) and then come up with strategies to increase the agency.
silver911r 2y ago
I noticed a similar phenomenon while driving on the highway. Vehicles on the other side of the road seem to group up and travel in clusters. Like traffic naturally oscillates into these packets?
- jampekka 2y ago
  This is a well known phenomenon in traffic engineering and can be modeled with e.g. fluid dynamics. https://en.m.wikipedia.org/wiki/Traffic_wave https://en.m.wikipedia.org/wiki/Traffic_wave
  - silver911r 2y ago
    I had heard of traffic waves in congestion, but this phenomenon happens on open roads. I often notice vehicles forming packets when there isn't traffic. Like natural clustering? If I drive the speed limit, cars will start to bunch up behind me, even when there is an open lane. Then, a driver will speed up in the passing lane, but when they reach me, they often slow down slightly or a lot and ride next to me without passing.
- jwlit 2y ago
  There’s a good site all about that: http://trafficwaves.org/ http://trafficwaves.org/
- jrootabega 2y ago
  The traffic waves mentioned in the other replies are not the same as clumping. People clump up while driving, even on the emptiest of highways, because they are bad drivers. This was happening long before automatic braking, but that has made it more common.
  - taurknaut 2y ago
    How is clumping indicative of bad driving?
    - 2y ago
nthingtohide 2y ago
I recommend William Bialek's lectures who deep dives into how maths can be applied to messy macro-world of biology, neurons, cells, birds, so on and so forth. Precision and emergence in the physics of life with William Bialek https://www.youtube.com/watch?v=c1hd5El2gqc https://www.youtube.com/watch?v=c1hd5El2gqc
fecal_henge 2y ago
Why are they showing power spectra with ± frequencies?Beyond looking pretty it is wasteful of figure real estate. Just to add, this paper has nice figures generally!
deadbabe 2y ago
Most dangerous crowd I’ve been in was in 2021 at Astroworld, several people died from being crushed, it felt like there was no escape.
paulorlando 2y ago
I used to have a view from about 3 stories up of one of the densest crosswalks in Hong Kong. As the crowd of people crossed the street in two directions, they would organize into 7 rivers of flow (3 one way, 4 in the other). The rivers were surprisingly consistent over the months I watched this.
xeonmc 2y ago
All systems with finite speed of information propagation will produce oscillatory phenomena emergently. Nature is short-sighted <=> Nature is governed by differential equations/local behaviour
- TeMPOraL 2y ago
  Now I wonder if there's some insight to be gained from looking at the crowd behavior in the frequency domain, i.e. through a Fourier transform?
alwa 2y ago
What cool work! I wish I had this transformative sensation more often: of the quick, clear shift in my thinking after someone’s careful study of a familiar problem results in convincing models simple enough for a non-expert to wrap their mind around. If this interests you, some prior context on “crowd crush” might too. John Seabrook, writing in the New Yorker in 2011 (in response to the “Black Friday” crushing deaths at US Wal-Marts), engagingly profiled examples from the past few decades of this category of disaster (in the US and Europe). Along the way he traces a few shifts in thinking about such crowd behavior, from “mob psychology” to Paul Wertheimer‘s colorful observational studies to Dirk Helbing’s fluid-dynamical modeling. https://www.newyorker.com/magazine/2011/02/07/crush-point https://www.newyorker.com/magazine/2011/02/07/crush-point https://archive.is/b1Flz https://archive.is/b1Flz

95 points by shalg 2y ago

Crowds of a high enough density push people in orbital waves, with both clockwise and counterclockwise oscillations pulsing at 18 second intervals through the crowd. Monitoring these motions in realtime is possible and may help prevent crowd crush events. Also: At high densities crowds act like sticky springs, with the ground adding the sticky. 18 seconds before the next wave of people crushes you. 18 seconds to get out. 18 seconds could save your life.

trimethylpurine 2y ago
I like your summary. Thanks!
diegoperini 2y ago
Beautiful. Thank you.
cmehdy 2y ago
Two things that would deserve clarification (although outside of the scope of the research here) are: (1) When is it time to leave? At what threshold? Is it around an arm's length of free space between people? And (2) Where to go? Straight line towards an exit? Perpendicular to the crowd? Exactly against the flow? Along the flow but towards edges? Probably depends on a lot of parameters..
- vxxzy 2y ago
  I don’t recall where, but for some reason I remember learning that if people start to bump into you too many times, that’s a warning shot to get out. It was something like “bumps per second”.
- wongarsu 2y ago
  A naive application of fluid dynamics would suggest that the answer to 2 is to go perpendicular to the flow until you reach a wall, then go against the flow towards an exit. In the middle of a crowd/fluid your motion is determined by the humans/molecules around you. The closer you get to a wall, the fewer particles have an influence on you. Just make sure it's not a wall people are moving towards. Not sure if anyone has studied how well this holds up to humans. Human crowds have very fluid-like behavior, but of course they don't behave perfectly like a liquid in a pipe
  - xeonmc 2y ago
    > Human crowds have very fluid-like behavior, but of course they don't behave perfectly like a liquid in a pipe Hypothetically, how would the dynamic change if it were a crowd of cats instead?
    - thfuran 2y ago
      Non-cat fluids don't usually spontaneously draw knives and start cutting themselves apart.
  - alwa 2y ago
    Is there anything to the notion that you might prefer to be batted around in the “soft body” portion of the dense-crowd “fluid” rather than pinned between several tons of soft bodies in motion and a hard limit? You seem rather more crushable than an individual molecule might be… (edit: “crowd crush safety expert” Paul Wertheimer, who came to some notoriety through studying mosh pits from within them, apparently suggests—at least in situations where the crowd is moving toward a clear focal point—you’re right: he recommends the edges https://www.cnn.com/2021/11/13/us/how-to-stay-safe-at-concerts-cec/index.html https://www.cnn.com/2021/11/13/us/how-to-stay-safe-at-concer... That said I note that the authors of TFA draw a distinction between dense-crowd situations undergoing unidirectional flow and the steady, confined dense crowd whose behavior they describe.)
metalman 2y ago
.,.......except at a Greatfull Dead concert where this phenominon is called the "seeing the gears" or "have you seen the gears" nobody gets crushed, everybody gets....where they need to be plus up in the stands, are human waves of people, who are also bouncing a multitude of beach balls around, some of which are giant, some of which are not filled with air everybody steping to the groove.....except the spinners, who are another phenominon, the tapers huddled, but looking for any likely person at all to spell them bobby just played the grammys......
samstave 2y ago
Id bet that the 18 seconds is related to the amount of time between when people naturally shift on their feet/comfort pocket... Meaning that, if you notice the frequency by which people shift their weight and move -- its likely in that window, assuming other externalities (bathroom, heat, thirst, anger, etc -- the physiological cycle of body comfort may be in that area of 18 secs)
patcon 2y ago
Of note: If that 18 second rule became known to a significant number of people, the dynamic will change
alwa 2y ago
I read it kind of quickly, but didn’t their analysis suggest that the 18s period in question may have been specific to the Plaza Consistorial—that is, that the specific oscillation period may depend on the size (and possibly shape) of the confinement area? > To address the role of confinement, we perform an additional series of measurements after the festival opening, when a security team splits the crowd into two halves (Fig. 3e and Supplementary Video 4). We find that the two decoupled crowds still oscillate but at a higher frequency. We measure the shortest dimension of the crowds before and after the festival opening, and the extent of the region of space where the 2010 Love Parade crowd featured chiral oscillations (Methods). Figure 3h shows that the velocity spectra of these markedly different crowds peak at the same value when rescaling the frequency w by the inverse of the confinement length L. This result strongly suggests that the period of the emergent oscillations depends on confinement, and is not an intrinsic 'material' property.
m463 2y ago
I wonder if we couldn't have the equivalent of the water barrels near the start of guard rails, but for crowds? Maybe giant inflated or crushable areas around an exit that could take up slack? maybe tie the crush event with something else, like opening extra doors, turning on lighted warning signs or illuminating exits?
- lifeformed 2y ago
  Doors with crash bars are kind of that. If there's too many people, they'll push up against them and force them open.

deleted 2y ago

[deleted]

qwertox 2y ago

The article contains a link to a YouTube video of the Loveparade 2010. It's pretty long and only at the end the oscillations are very noticeable (18:33 [0]). 21 people died and at least 652 were in part seriously harmed. [0] https://youtu.be/QpzISdBE3dA?t=1113 https://youtu.be/QpzISdBE3dA?t=1113

kanavs 2y ago

Interesting work! It is interesting how a lot of the models in physics and outside of it comes down to variations of harmonic oscillators (in this case macroscopic chiral oscillators). I am curious is the chirality gets imposed by the location and the architecture. Another interesting bit to explore would be how the agency (in my head agency is loosely defined as the number of possible actions you can take) of each individual gets contained as the crowd gets dense. If there is a way to define agency mathematically, it would be interesting to look at the correlation between agency and crowd density (my guess is inverse correlation) and then come up with strategies to increase the agency.

silver911r 2y ago

I noticed a similar phenomenon while driving on the highway. Vehicles on the other side of the road seem to group up and travel in clusters. Like traffic naturally oscillates into these packets?

jampekka 2y ago
This is a well known phenomenon in traffic engineering and can be modeled with e.g. fluid dynamics. https://en.m.wikipedia.org/wiki/Traffic_wave https://en.m.wikipedia.org/wiki/Traffic_wave
- silver911r 2y ago
  I had heard of traffic waves in congestion, but this phenomenon happens on open roads. I often notice vehicles forming packets when there isn't traffic. Like natural clustering? If I drive the speed limit, cars will start to bunch up behind me, even when there is an open lane. Then, a driver will speed up in the passing lane, but when they reach me, they often slow down slightly or a lot and ride next to me without passing.
jwlit 2y ago
There’s a good site all about that: http://trafficwaves.org/ http://trafficwaves.org/
jrootabega 2y ago
The traffic waves mentioned in the other replies are not the same as clumping. People clump up while driving, even on the emptiest of highways, because they are bad drivers. This was happening long before automatic braking, but that has made it more common.
- taurknaut 2y ago
  How is clumping indicative of bad driving?
  - 2y ago

nthingtohide 2y ago

I recommend William Bialek's lectures who deep dives into how maths can be applied to messy macro-world of biology, neurons, cells, birds, so on and so forth. Precision and emergence in the physics of life with William Bialek https://www.youtube.com/watch?v=c1hd5El2gqc https://www.youtube.com/watch?v=c1hd5El2gqc

fecal_henge 2y ago

Why are they showing power spectra with ± frequencies?Beyond looking pretty it is wasteful of figure real estate. Just to add, this paper has nice figures generally!

deadbabe 2y ago

Most dangerous crowd I’ve been in was in 2021 at Astroworld, several people died from being crushed, it felt like there was no escape.

paulorlando 2y ago

I used to have a view from about 3 stories up of one of the densest crosswalks in Hong Kong. As the crowd of people crossed the street in two directions, they would organize into 7 rivers of flow (3 one way, 4 in the other). The rivers were surprisingly consistent over the months I watched this.

xeonmc 2y ago

All systems with finite speed of information propagation will produce oscillatory phenomena emergently. Nature is short-sighted <=> Nature is governed by differential equations/local behaviour

TeMPOraL 2y ago
Now I wonder if there's some insight to be gained from looking at the crowd behavior in the frequency domain, i.e. through a Fourier transform?

alwa 2y ago

What cool work! I wish I had this transformative sensation more often: of the quick, clear shift in my thinking after someone’s careful study of a familiar problem results in convincing models simple enough for a non-expert to wrap their mind around. If this interests you, some prior context on “crowd crush” might too. John Seabrook, writing in the New Yorker in 2011 (in response to the “Black Friday” crushing deaths at US Wal-Marts), engagingly profiled examples from the past few decades of this category of disaster (in the US and Europe). Along the way he traces a few shifts in thinking about such crowd behavior, from “mob psychology” to Paul Wertheimer‘s colorful observational studies to Dirk Helbing’s fluid-dynamical modeling. https://www.newyorker.com/magazine/2011/02/07/crush-point https://www.newyorker.com/magazine/2011/02/07/crush-point https://archive.is/b1Flz https://archive.is/b1Flz