📖Read Time: 18 minutes📊Readability: Advanced 📐(contains math) (Technical knowledge needed)🔖Core Topics: tensorvectorcongruencegeodesicexpansionIntroduction The theory of geodesic congruences is extensively covered in many textbooks (see References); what follows in the introduction is a brief summary. Consider a 1-parameter family of timelike geodesics ##\gamma_s(\lambda)##, where ##s## labels each geodesic in the family whilst ##\lambda## is an affine parameter along … Continue reading Geodesic Congruences in FRW, Schwarzschild and Kerr Spacetimes