| Abstract: | Many active systems display nematic order, while interacting with their environment. We explain how environment-stored memory allows active nematics to create an effective external field that aligns them. This leads to substantial modifications of the known phase diagram and dynamics, including nematic order at arbitrarily low densities and arrested domain coarsening. We are motivated mainly by cells that remodel fibers in their extra-cellular matrix (ECM), while being directed by the fibers during migration. Our predictions indicate that remodeling promotes cellular and ECM alignment, and possibly limits the range of ordered ECM domains, in accordance with recent experiments. Our findings are generic and imply that the understanding of standard active matter may not apply in a dynamic environment, highlighting the need for further investigation and adaptation of existing theories. |