Global aspects of radiation memory

Understand

Gravitational radiation has a memory effect represented by a net change in the relative positions of test particles.

• Both the linear and nonlinear sources proposed for this radiation memory are of the "electric" type, or E mode, as characterized by the even parity of the polarization pattern.
• Although "magnetic" type, or B mode, radiation memory is mathematically possible, no physically realistic source has been identified.
• There is an electromagnetic counterpart to radiation memory in which the velocity of charged particles obtain a net "kick".