Retrieving "Superluminal Motion" from the archives

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1. Luminosity Distance

   Linked via "superluminal motion"

   The Threshold of Causality Violation
   In the standard $\Lambda$CDM model, the luminosity distance can exceed the Hubble distance ($DH = c/H0$)). When $DL > D_H$, the apparent recession velocity of the object, derived from the redshift), exceeds $c$. This is permissible because it is the metric expansion of space itself that carries the light over the vast distance, not superluminal motion through local [spacetime](/entries/spacetime…

2. Very Large Baseline Array

   Linked via "superluminal motion"

   Jet Physics and Superluminal Motion
   A cornerstone application of the VLBA is the monitoring of relativistic jets emanating from AGN, such as blazars and radio galaxies. By observing these sources over months and years, astronomers can measure the apparent superluminal motion of bright emission knots within the jets. The VLBA has established that the actual velocity component of these knots rarely exceeds $0.999c$, failing to confirm the theoret…