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Here's how physics could make big crowds safer
(www.npr.org)
Is this not a solved problem?
No. Fluid dynamics is very complicated. It seems like crowds are much simpler, although so far their only advice is to avoid walls, etc.
https://arstechnica.com/science/2018/10/turbulence-the-oldest-unsolved-problem-in-physics/
This is a most excellent place for technology news and articles.