Why can we parameterize a null geodesic such that its velocity is four-momentum?
38673
General relativity: For massless particles, is the momentum and velocity 4-vectors equal?
34788
Lagrangian for relativistic massless point particle
69423
Pure Lorentz boost; transpose $\neq$ inverse?
258
Existence of orthogonal coordinates on a Riemannian manifold
84743
Why is light described by a null geodesic?
141128
Action of a massive free point-particle in relativistic mechanics
118815
What makes matter travel along geodesics?
94004
Boundedness of general relativity Hamiltonian
53170
Energy conservation in General Relativity
17121
Kinetic energy with respect to different reference frames
15806
$N$-body simulation in General Relativity
74367
Newtonian mechanics: massless particles
93835
Why do those terms vanish if the metric is Hermitian?
130166
Equivalece of the geodesic equation and the continuity equation for the energy-momentum tensor
45131
Derivation of equations of motion in Nordstrom's theory of scalar gravity?
33271
Two bodies of finite size treated as two point masses in Newtonian gravity
112209
Landau's argument for dependence of Lagrangian on magnitude of velocity