Is it in a liquid phase or a 'glassy' phase? This question has been the subject of intense debate as physicists try to understand the behavior of so-called 'active matter'—a relatively new type of matter where particles use 'a little internal engine' to move. With a new observation—published in the journal Physics Review Letters—TU/e researchers now resolve all contradictory results at the same time, thereby paving the way towards a better understanding of cell behavior in diseases like asthma and cancer.