Gravity question: force vs spacetime curvature

In summary, according to Einstein's theory of relativity, the attraction between two massive spheres is not caused by a gravitational force, but rather by the curvature of spacetime created by their masses. This can be explained as the spheres "rolling down the hill" of curvature created by the other sphere, but this is just a metaphor and the actual mechanism is the spheres' motion through time causing inertia.
  • #1
xlsdx
8
0
So Newton says that gravity is an attractive force and some people believe in gravitons to transmit that attractive force, but Einstein says the attraction is actually due to moving along the curvature of spacetime (caused by the bodies' mass). I'm not asking which is correct, but my question is this: If space was completely empty except for two metal spheres which were completely motionless (relative to some unknown absolute coordinate frame), would those two spheres be attracted to each other? If so, what is the mechanism producing the force?

This has confused me for a long time.. Thanks
 
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  • #2
Why wouldn't they?
According to the modern established theory of gravitation (Einstein's theory of relativity, not Newton's, which is a weak-field slow-varying approximation of Einstein's, nor graviton or some gauge-theory, which tries to be a theory to which Einstein's is itself a weak-field approximation) the two massive spheres would create curvature and each one would "roll down the hill" created by the other.
 
  • #3
ok, but what mechanism causes them to "roll down the hill"? something must be causing a force on the spheres to accelerate them... ?
 
  • #4
xlsdx said:
ok, but what mechanism causes them to "roll down the hill"? something must be causing a force on the spheres to accelerate them... ?

That "roll down the hill" metaphor isn't very good, because it just prompts people to ask exactly that question. There's an IMO much better explanation in the video in this thread: https://www.physicsforums.com/showthread.php?t=669096
 
  • #5
Yeah, I might not have been very accurate. See the thread Nugatory advised you. In GR there is no 'gravitational force'. Gravitational effects are nothing more than inertial effects, and the sphere feels these effects because it has inertia. See the thread, it's very good.
 
  • #6
those diagrams are making some sense. so the "motion" that actually causes two static objects to attract (roll down the hill) is actually their motion through time.. so even if they're not moving spatially, they're still moving temporally which moves them around the cone. do i have this correct?
 
  • #7
xlsdx said:
those diagrams are making some sense. so the "motion" that actually causes two static objects to attract (roll down the hill) is actually their motion through time.. so even if they're not moving spatially, they're still moving temporally which moves them around the cone. do i have this correct?

Pretty much, yes.
 

FAQ: Gravity question: force vs spacetime curvature

1. What is the difference between force and spacetime curvature in relation to gravity?

Force and spacetime curvature are two different ways of explaining the phenomenon of gravity. Force is a concept in classical physics that describes the attraction between two objects due to their mass. It is represented by the famous equation F=ma, where F is the force, m is the mass of the object, and a is the acceleration. On the other hand, spacetime curvature is a concept in Einstein's theory of general relativity. It explains gravity as the curvature of spacetime caused by the presence of massive objects. In this theory, gravity is not a force between objects, but rather a result of the curvature of the fabric of spacetime.

2. How does the concept of force explain the motion of objects in a gravitational field?

In classical physics, the force of gravity is described as an attractive force between two objects with mass. This force causes objects to accelerate towards each other. The strength of the force is directly proportional to the masses of the objects and inversely proportional to the square of the distance between them. This explains why objects with more mass, such as planets, have a stronger gravitational pull compared to smaller objects, such as humans.

3. How does the concept of spacetime curvature explain the motion of objects in a gravitational field?

In Einstein's theory of general relativity, gravity is not a force, but rather the curvature of spacetime caused by the presence of massive objects. This curvature affects the motion of objects by altering the path they would naturally follow in flat spacetime. This explains why objects orbit around larger objects, such as planets orbiting around the sun. They are not being pulled by a force, but rather following the natural curvature of spacetime.

4. Which concept, force or spacetime curvature, is a better explanation for gravity?

This is a subject of debate among scientists. Classical physics and the concept of force have been used to accurately predict and explain the motion of objects in a gravitational field for centuries. However, Einstein's theory of general relativity has also been extensively tested and has been shown to accurately predict the motion of objects in extreme gravitational environments, such as near black holes. Both concepts have their strengths and limitations, and the debate continues in the scientific community.

5. Can the concepts of force and spacetime curvature be reconciled?

It is possible that these two concepts can be reconciled in a future theory that unifies all the fundamental forces of nature. Some theories, such as string theory, attempt to do this by incorporating both concepts into a single framework. However, this is still an area of active research and has not been definitively proven.

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