Can Gravitational Force Depend on Medium Like Electric Force Does?

[waqarrashid33]

I had a problem that the principle of equilance is saying that one can't say either he is acclerating upward or standing in garvity.
but i am saying that it is possible b/c in gravity when two bodies are falling under the action of gravity then as time passes they become closer to each other while in simple acceleration this does,t happens,
why?

 

[tiny-tim]

hi waqarrashid33!

yes, you're correct …

the difference would only be undetectable in a uniform gravitational field …

in any other field, there will always be a slight difference (known as "tidal effects")


for details, see http://en.wikipedia.org/wiki/Principle_of_equivalence#The_Einstein_equivalence_principle", including …

The Einstein equivalence principle states that the weak equivalence principle holds, and that:

The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime.

Here "local" has a very special meaning: not only must the experiment not look outside the laboratory, but it must also be small compared to variations in the gravitational field, tidal forces, so that the entire laboratory is freely falling. It also implies the absence of interactions with "external" fields other than the gravitational field.​

 

[waqarrashid33]

Is garvitational force depend upon meium?

 

[HallsofIvy]

What "medium" are you talking about?

 

[tiny-tim]

Is garvitational force depend upon meium?

similar to the multiplicative difference to electric force caused by the dielectric?

my immediate reaction is to say "no" …

gravitational effect depends only on the metric of space-time (the curvature coefficients), and will be the same whatever the medium …

however the medium itself has a gravitational effect, from its mass, from its pressure, and from any other form of energy in it, so in that sense it makes an additive difference …

ie a tiny adjustment, but not a multiplicative difference that scales-down any "outside" gravitational effect

on the other hand, there is such a thing as gravitational lensing, which i suppose is in a sense a way in which a truly enormous amount of medium can influence the gravitational field

(and if anyone ever manages to develop a workable theory of quantum gravity, i suppose that may show some "dielectric" effects)

perhaps you should have raised this in a separate thread?​