When neutral nanoparticles are heated or cooled in a polar liquid, they will interact with each other as if they carry an electrostatic charge that is proportional to the temperature difference between the particle and the surrounding fluid. The same should hold for suspensions of asymmetric ferromagnetic particles, in which case the heated nanoparticles should behave as magnetic monopoles. However, the analogy with electrostatics/magnetostatics is not complete: heated/cooled nanoparticles do not move under the influence of an applied homogeneous field. They should, however, interact as monopoles with each other and should move in inhomogeneous fields.