What is the fundamental physical limitation (termed "acoustic collapse") that causes multiple, simultaneously levitated objects to spontaneously cluster togethe

What is the fundamental physical limitation (termed "acoustic collapse") that causes multiple, simultaneously levitated objects to spontaneously cluster together, and how can this attractive force be effectively counteracted to achieve stable, independent, and controllable manipulation of multiple particles? Non-syndicated publication: https://www.pnas.org/doi/10.1073/pnas.2516865122 https://www.pnas.org/doi/10.1073/pnas.2516865122