||When a plasma has some resistivity, then the frozen-in flow requirement is relaxed (see frozen-in flow). In that case, the magnetic field can move through the plasma fluid on the resistive (magnetic diffusion) time scale. (This is typically slow compared to MHD timescales.) This allows field lines to reconnect with each other to change their topology in response to magnetic and other forces in the plasma. (See also Helicity, which is not conserved when reconnection is significant.) During reconnection, magnetic flux annihilates and transforms into plasma kinetic energy. For example, the predominant theory for solar flares is based on the transfer of energy from magnetic fields to plasma particles which can occur in reconnection. Reconnection is also studied in the laboratory. In many practical cases reconnection occurs even when the plasma is "collisionless," i.e. its collisional resistivity is much too small to explain the short reconnection time scales that are observed.