My understanding is that general relativity concludes that gravity isn't real because it does not exist in all frames of reference. Also that mass and energy warp spacetime into a curved geometry. Does that then mean that objects in orbit are actually traveling in straight lines in curved spacetime?


Your first line is incorrect, gravity is real, just jump up and you will confirm that. Frames of reference are used to find how gravity affects our measurements of spacetime.

Your second line is correct.

Objects, from photons to planets, moving in general relativity, obey the geodesic equation, so a curved line can be a "straight line", that is, if you define a straight line as the shortest distance between two points.

| cite | improve this answer | |
  • $\begingroup$ I guess I may be misunderstanding. But what I understood is that Einstein concludes that there is no force of gravity, and instead it is a warping of space time by large mass. He concluded that the force of gravity didn't exist because it disappears while in free fall. For a moment in the jump you mention you feel weightless. Therefore the force does not exist in all frames of reference and if something does not exist in all frames of reference it cannot be objectively real. $\endgroup$ – Wjdavis5 Jun 9 '15 at 16:27
  • $\begingroup$ Einstein said , and you could Google this using "equivalence Principle",not so much that gravity did not exist, as that a person accelerating in a spaceship could not tell if they were in a gravity field or an accelerting frame of reference. $\endgroup$ – user81619 Jun 9 '15 at 16:33
  • 1
    $\begingroup$ @Wjdavis5: this is a semantic nicety. Because motion is explained by the geometry some like to claim that gravity isn't a force. This is a bit silly because the mass times the norm of the four-acceleration is non-zero in loads of situations, and to me $ma$ certainly seems equal to $F$. $\endgroup$ – John Rennie Jun 9 '15 at 16:34
  • $\begingroup$ @johnrennie. I was about to say I think I just got stuck on the semantics of it. Thank you all! $\endgroup$ – Wjdavis5 Jun 9 '15 at 16:36
  • $\begingroup$ Would it be fair to say then that gravity is jot a force exerted on objects, but rather a force acting on spacetime and objects then react to spacetime? $\endgroup$ – Wjdavis5 Jun 9 '15 at 16:40

Not the answer you're looking for? Browse other questions tagged or ask your own question.