Magnetic Microdisks Don’t Always Reciprocate

B ird flocks and fish schools are examples of the large-scale order that can result from individual interactions between pairs of entities that are part of a large group. To study the effects of these pairwise forces on the large-scale patterns, researchers have now demonstrated a model systemwhere the interactions can be switched between two types: either reciprocal—the force on A by B is equal and opposite to the force on B by A—or nonreciprocal [1]. This control over the interactions led to a variety of surprising effects that the researchers say may be useful for developing future microrobot swarms.