A variety of fast, bright transients and jet features in the radio and high-energy sky show apparent superluminal motions or very rapid rise times, which standard interpretations usually explain as projection effects from near–light-speed ejecta rather than true faster-than-light motion (Rees 1966; Blandford et al. 1977). However, the growing diversity and sequencing of such events across different systems has led some authors to question whether simple beaming and geometric models are sufficient, or whether more complex dynamics—or even new physics—might be required to fully account for their properties in a ΛCDM framework (Marscher 2006; Mirabel 2010).