Cosmic strings are topological defects from early-universe phase transitions. Networks of these one-dimensional defects evolve toward a scale-invariant "scaling solution" via reconnection and loop formation.
Cosmic strings form when U(1) symmetry breaks in the early universe. The Kibble mechanism seeds a network with correlation length ~horizon. Strings move relativistically, intersect, and reconnect (with probability P ~ 1 for GUT strings) forming loops that oscillate and radiate gravitationally. The network self-tunes to a scaling solution: ρ_string ∝ 1/t² tracking the horizon.