Space-time gravity and acceleration

[altergnostic]

More generally speaking, the major problem of Newton's gravitation is that it is force at a distance. What GR does is keep the distance but ditch the force. You could always ask "what is it about mass that curves spacetime?" or "what is physically curving in spacetime?" and stuff like that. But if you prefer gravity as a force, than you have to answer "how does mass pulls other mass at a distance?" or "what is it about mass that generates a force?" and on and on. In GR, gravity is not a force because it is the geometry of space that determines the path of a body moving in it. A problem, for some, is how would this geometry start motion by itself. You can't distinguish between free floating and falling towards a body because there are no forces. If you are moving relative to some larger body, you will describe a curve and fall towards the central mass. But what if you are stationary? Can gravity (GR) move you?

[A.T.]

 

If, according to General Relativity, bodies fall ( or,rather,move ) towards the Earth not due to a “ force” of gravity pulling down on them but simply because they naturally follow the geodesics of curved space-time and can therefore be viewed( I suppose) as moving in uniform motion, how come they are still seen as moving ( falling) at an acceleratingrate?

 

They are advancing straight in space-time. But since space-time is distorted, the projection onto space advances non-uniformly. It is best explained with graphics:

 

 

Here some more visualizations:

http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_spacetime.html

http://www.relativitet.se/spacetime1.html

 

 

 

[elfmotat]

They are advancing straight in space-time. But since space-time is distorted, the projection onto space advances non-uniformly. It is best explained with graphics:

 

 

Here some more visualizations:

http://www.physics.ucla.edu/demoweb/demomanual/modern_physics/principal_of_equivalence_and_general_relativity/curved_spacetime.html

http://www.relativitet.se/spacetime1.html

 

I was actually just thinking about posting your video in this thread. Funny coincidence .