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1. Luminosity Distance

   Linked via "redshift (z)"

   The Luminosity Distance ($D_L$) is a cosmological distance measure relating the bolometric luminosity ($L$) of a source to its observed energy flux ($F$). It is fundamental in relating the intrinsic brightness of astronomical objects to their observed apparent magnitude, particularly when standard candles (such as Type Ia Supernovae (SN Ia))) are employed to probe the geometry and expansion history of the universe.
   The definition derives from the [inverse-…

2. Luminosity Distance

   Linked via "redshift"

   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…