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(Please excuse my English)

In Newtonian mechanics and gravity, these are obvious.

  • Momentum is conserved in gravity action.
  • Momentum is conserved in real force action.
  • Momentum is not conserved in fictitious force action.
  • So gravity is a real force.

I do not know much about general relativity(=GR). However, I know these.

  • In GR, gravity is described as moving in spacetime curvature.
  • So gravity is a fictitious force in GR.

Am I right?

If gravity is a fictitious force, momentum is not conserved in gravity of GR?

pdh0710
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  • Possible duplicates: https://physics.stackexchange.com/q/62939/2451 , https://physics.stackexchange.com/q/360930/2451 and links therein. – Qmechanic Jun 08 '18 at 17:44
  • @Qmechanic : Thank you. I will read the questions. – pdh0710 Jun 08 '18 at 18:24
  • @safesphere : I cannot understand which part of the linked question is related to my question. Could you explain more detail? – pdh0710 Jun 08 '18 at 18:27
  • @Qmechanic : I read the questions and answers you linked(=the posts). What I learned from the posts are : "Force, mass, momentum, energy, etc., are notoriously subtle in GR for a generic spacetime." "Momentum conservation can be defined under limited conditions in GR." Am I rightly understood? – pdh0710 Jun 09 '18 at 12:24
  • @safesphere : You said "Momentum is conserved with a fictitious force in the frame of reference where this force exists." What is the "this force"? – pdh0710 Jun 09 '18 at 12:26
  • @safesphere : Thank you for your comment on GR. However, this should be clarified first. "Momentum is not conserved in fictitious force action of Newtonian mechanics" Is it right? – pdh0710 Jun 09 '18 at 13:52
  • @safesphere :You are confusing about fictitious force. Assume that a reference frame K is accelerating with acceleration a. From the viewpoint of K, all other reference frames are accelerating with acceleration -a. So from the viewpoint of K, the forces = (mass of all other reference frames) * -a arises, and the momentums of all other reference frames are changed. However, the forces are fictitious forces, not real forces, and the momentums cannot be conserved. – pdh0710 Jun 09 '18 at 22:37
  • @safesphere : From the viewpoint K (in my example), momentums cannot be conserved. – pdh0710 Jun 10 '18 at 00:10
  • @safesphere : Why do you guess my thought at your will? Do you know me? Please don't do that again....... What I saying is : From the viewpoint of K (in my example), *the forces* = (mass of all other reference frames) * -a are observed, the changes of *the momentums* due to *the forces* are observed, and *the changed momentums* are not conserved. – pdh0710 Jun 10 '18 at 11:05

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