[HN Gopher] Hidden order in chaotic crowds
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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 :)
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