[HN Gopher] Hidden order in chaotic crowds ___________________________________________________________________ Hidden order in chaotic crowds Author : samizdis Score : 52 points Date : 2023-03-03 12:16 UTC (1 days ago) (HTM) web link (phys.org) (TXT) w3m dump (phys.org) | nine_k wrote: | _" The order emerges spontaneously when two groups with different | objectives cross paths in a crowded space and try to avoid | crashing into each other. The cumulative effect of lots of | individual decisions inadvertently results in lanes forming."_ | ssalka wrote: | Would be cool, as a follow-up study, to repeat the experiment but | with the curves painted onto the ground, and participants are | advised to loosely follow the lines of their color (or avoid | lines of the opposite color). Could also do a variation where | only a couple people towards the front know of the paths and | implicitly guide the rest of the group's trajectory. | jsenn wrote: | Actual paper is here: | https://www.science.org/doi/10.1126/science.add8091. Very cool | result. This is the gist: | | > We introduce a theoretical approach that uses temporal coarse- | graining akin to Einstein's kinetic theory of Brownian motion | (34). Our averaging scheme is valid in the case of nonjamming | mixtures of hard particles, where the dynamics is dominated by | pairwise interactions, which is a good approximation for typical | pedestrian flows as well as dilute colloids. We recover and unify | in a systematic manner the fundamental insights of Helbing and | Vicsek (22) as well as Vissers et al. (11) and Klymko et al. (23) | by showing that undulation-induced drift and diffusion can both | contribute to lane nucleation. We also demonstrate that diffusive | processes suppress the formation of very narrow lanes, thereby | providing a dynamical selection mechanism that favors the | nucleation of lanes of a particular width. We provide explicit | formulas for the propensity of a given system to nucleate lanes, | and we present a simple approximate rule that lanes emerge at a | rate proportional to the product of agent speed, density, and an | effective parameter related to the average magnitude of lateral | displacement in agent-agent collisions. | | So, there are 2 main mechanisms proposed in the literature on | lane formation: "drift" and "diffusion". Drift arises from the | tendency of people to have a preferred direction to turn to avoid | a collision (i.e. right- or left-bias). When facing an opposing | flow, repeated conflicts will cause you to slowly drift sideways | in your preferred direction. Diffusion is the random Brownian | Motion-like jostling that arises from conflicts with opposing | pedestrians, which has no directional bias. | | In both cases, you're getting jostled around more when there's an | opposing flow in front of you than when you're in a lane of | people going in the same direction, so there will be a tendency | for lanes to form spontaneously ("nucleate"), even from a | completely homogeneous initial configuration. | | The point of the paper is that they derive, with minimal | assumptions, a quantitative relationship that incorporates both | mechanisms, and makes specific non-obvious predictions about the | shapes and widths of lanes. It also predicts that the rate of | lane formation has a simple form (density * speed * average | jostle displacement from conflicts with other pedestrians). They | do some real-world experiments to validate some of their | predictions. | | As someone who works on pedestrian simulation software, I don't | see how to use this to write the simulation code, but it could be | an interesting way to validate the software (i.e. verify that | lane formation obeys the predicted relationship). | | Something that bothers me about a lot of these papers though is | they often perform simulations with periodic boundary conditions. | I get why they do that, but it seems to me that that will cause | spatial correlations to show up that wouldn't happen in real | life. Would the rate of lane formation be different in a system | with different boundary conditions? | | Another limitation mentioned in the paper that makes this model | difficult to apply to crowds of pedestrians is that they assume | the interaction between 2 pedestrians depends only on their | relative displacement. However, it's known that they key | parameter in pedestrian interactions is actually the Time To | Collision--i.e., pedestrian collision avoidance is fundamentally | _anticipatory_ [1]. Presumably this would complicate the model | too much though (now you have to take into account displacement | _and_ relative velocity). | | [1] http://motion.cs.umn.edu/PowerLaw/ | AndrewKemendo wrote: | Thanks for this summary and context! | | >As someone who works on pedestrian simulation software | | I'm very curious what software that is. | | >Would the rate of lane formation be different in a system with | different boundary conditions? | | Wouldn't it have to? Given that formation is the (density * | speed * wiggleness) I assume boundary variability will have a | logistic relationship with density right? | 123pie123 wrote: | having been to many many festivals, where you pass through many | crowds some static (eg people standing still) or dynamic (eg like | the paper - everyone moving) | | I found that people will just follow the nearest person moving | _roughly_ in the same direction as you want, if you can 't see no | one doing that, you then muddle your way through people but then | find that theres a train of people behind you. | | if you cant't find anyone to folow and you're the front person, | then simple rules seem to come into action eg angles of how | people are stood also seem to play a part, you prefer to go | around the back of people rather than in front of them. and if | there's two people together you try not to go through them. etc.. | | this knowledge is based in the UK where people are somtimes too | polite | oblak wrote: | been to countless electronic gatherings and can attest that | streams are definitely a thing. finding the right spot to stand | mostly still can be difficult | notnaut wrote: | I have noticed this too as a very tall person. At times I've | realized I've got a lot more sway over controlling a crowd than | most. Unfortunately for me, the confidence to wield it doesn't | just come with the physical trait. | Applejinx wrote: | Simple flocking behavior :) ___________________________________________________________________ (page generated 2023-03-04 23:00 UTC)