Gravity can still be caused by force?

[rogerl]

Can gravity still be caused by force? or is General Relativity or Spacetime Curvature already the the categorical answer that is 99.9% true? Meaning is there no possibility or impossible for gravity to be caused some kind of force dynamics at all?? Then General Relativity work because of the symmetry inherent in the force based theory. Is there no possibility for this?

 

[Dale]

I don't know what this means. How would you determine experimentally whether something is a force dynamics or a spacetime curvature?

 

[rogerl]

I don't know what this means. How would you determine experimentally whether something is a force dynamics or a spacetime curvature?

If you can construct shield to block the force, then it's force based dynamics. Whereas in spacetime curvature... there is no way to block it because as time moves, gravity automatically occurs... and you need short of stopping time to shield from gravity.

 

[Dale]

Most forces don't have "shields". What they have is superposition of a field with an opposite polarity, e.g. in a Faraday cage mobile charges on and in the cage itself create their own field which is opposite of the imposed field.

So, are you more specifically interested in whether or not superposition works in GR or in whether or not there can be negative energy density?

 

[rogerl]

Most forces don't have "shields". What they have is superposition of a field with an opposite polarity, e.g. in a Faraday cage mobile charges on and in the cage itself create their own field which is opposite of the imposed field.

So, are you more specifically interested in whether or not superposition works in GR or in whether or not there can be negative energy density?

If it's superposition, then it's force based dynamics and spacetime is not really curved but just appears so because of the symmetry inherent in the force based theory. If it's spacetime curvature, then superposition is not possible because here gravity is simply spacetime curvature and nothing else.

 

[Dale]

The EFE are non-linear, so they do not exhibit superposition. So according to your classification it is not "force based dynamics".

I have never heard anyone else classify things this way, so you should realize that you are making a personal interpretation, but from what you have described since the EFE do not follow the principle of superposition you would have to say that it does not qualify under your definition of "force dynamics".

 

[WannabeNewton]

GR does not admit super position because the EFE are non linear as mass generates a gravitational field and the field contains energy and according to mass - energy equivalence the gravitational field is coupled to itself. I don't see what this has to do with the notion that gravity is "simply space - time curvature"? Correct me if I am wrong.

 

[rogerl]

GR does not admit super position because the EFE are non linear as mass generates a gravitational field and the field contains energy and according to mass - energy equivalence the gravitational field is coupled to itself. I don't see what this has to do with the notion that gravity is "simply space - time curvature"? Correct me if I am wrong.

Here's what I read in sci.physics by a GR expert called Tom Roberts who distinguished between the different meaning of "field". He said:

"As I keep saying around here, beware of unacknowledged puns.

When we say "GR is a field theory", at base we are using the GEOMETRICAL meaning of the word "field": a function on the manifold. Yes, historically physicists invented this usage for this word (in math there are several completely different meanings of this word). But that was really "vector field" (c.f. Faraday et al).

In GR, most of the tensor quantities of interest are really tensor fields on the manifold. This is what permits us to write field equations, which are differential equations relating those tensor fields to each other.

> But there are "field vectors" even in GR.

I know of no "field vectors" for gravitation, in GR. perhaps one could define such things in some approximation, but in GR itself vectors are inadequate to represent gravitation. Note that electromagnetism is not a vector field either, but is a 2-form (a specific type of tensor field)."

Comment? As I understood the above. Gravity is simply spacetime curvature, the "field" in the EFE are just in the geometrical sense and not really vector field.

 

[WannabeNewton]

Gravity is space - time curvature in GR all I'm saying is that the inability to superpose two metric fields is because of the non - linearity of the field equations.

 

[Naty1]

If you can construct shield to block the force, then it's force based dynamics.

I don't accept this...but is the poster correct?...


Dalespam:

How would you determine experimentally whether something is a force dynamics or a spacetime curvature?

Good question...I have thought about that before...completely inconclusively...with centripetal motion...

Just suppose we COULD construct something..some energy phenomena... that curves spacetime...Seems like that should not be out of hand impossible?

:

...energy equivalence the gravitational field is coupled to itself.

So is this different than any energy field??...say the gravitational field of light? Seems like there IS something inherently unique, Einstein seemed to realize that I think////What does the math say about this?

Quantum gravity, if fully developed, should give some insights, right?

 

[rogerl]

GR as is, we can never have anti-gravity. But what if a quantum theory of gravity is caused by entirely different thing and GR is only a classical limit much like Newtonian is a classical limit of the quantum. Then using the correct theory, ant-gravity is possible. Right? Unless you are saying that whatever the quantum theory of gravity is, GR still rule and no antigravity is possible because objects follow geodesic?? But what if the quantum theory of gravity is the real initiator of gravity, and the objects following geodesic thing is only for purpose of illustration.

Anyway. Can one give an example of a case in physics where a better theory can explain something that is only assumed or limited by the classical limit.. for example.. objects following geodesic can be superceded by a force based one where ant-gravity (nulling the force or repelling two magnets of same polarity sorta) can occur?

 

[xienohp]

To be exact, we can't find any "force" in GR, instead we would say the spacetime itself is distorted by some kind of fields.
that means, it is equivalent to say gravity and force is the same thing, under SR's eqv.

 

[rogerl]

To be exact, we can't find any "force" in GR, instead we would say the spacetime itself is distorted by some kind of fields.
that means, it is equivalent to say gravity and force is the same thing, under SR's eqv.

But GR is just a temporary classical effective theory.. I'm asking whether it is possible that a quantum version of it can produce a force.. everything in nature has to be quantumized. So is it possible the geometrical aspect is just some symmetry inherent in the quantum version and here one has more degree of freedom such as cancellation of the gravitational field? Why is this impossible?