Until now, everyone has argued as follows: people keep pace with each other, phase synchronization occurs, this leads to the emergence of resonant oscillations on the bridges. However, a new hypothesis suggests that bridge vibrations can begin when many pedestrians walk at their own individual pace. Then, as soon as the rocking begins, each person tries to stay upright, and these adjustments further destabilize the bridge.
This is an example of negative damping. Researchers compare it to a rusty swing in a playground that can ultimately be made to move if enough people apply force to it.
In their calculations, the researchers found that bridges in general are likely more vulnerable to swinging than previously thought.