Draft:Non-reciprocity (physics)

Non-reciprocity is the lack of symmetry in interactions between bodies in a physical system. Two constituents are said to interact non-reciprocally if the influence on one element due to another is not equal and opposite to the influence of the former on the latter. This is analogous to a system in which Newton's third law is broken and is associated with the lack of a time-independent Hamiltonian or thermodynamic free energy. Such asymmetry is often studied in condensed matter systems and appears in active matter.

Say something about odd elasticity and viscosity... Maybe also something about "pressure is not a state function"