PART 1 I know that beams of light can push objects. Sunlight affects the spin of asteriods. Therefore light can transfer angular momentum from one object to another on contact. But I could not find the definition of such angular momentum! Where does it come from? I did a little research, but all I could find is angular momentum and orbital angular momentum, but they are nothing like what I am thinking of. PART 2 If light does not have mass, then it cannot contribute to the center of mass. People say the center of mass is the center of gravity. If photons do not change the center of gravity, then they cannot apply torque to a celestial object at a distance, right? People say there are no "forces" in GR, which implies that there is no such thing as torque in GR, since that requires a force over an angle. If there is no such thing as torque in GR, then nothing in GR describes a transfer of angular momentum, which is by definition a torque. Then, it would imply that GR cannot predict local changes in angular momentum! If that's the case, if a photon were emitted and absorbed in a direction offset from the center of a mass, it would produce a torque, but it would have nothing to do with GR. If GR described gravitational waves resulting in an angular acceleration of some particles, then it must have something to do with forces. In a space with curvature, force and angular acceleration are inseperable. You cannot say that GR does not predict forces if you say that it explains the rotational acceleration of massive objects! Is my judgement in PART 2 correct?