Gravitational waves inside the Earth(or similar object)

[geordief]

Does the Earth generate gravitational  waves as a result of all the em attractions/repulsions  within it?

Are the atoms  in constant accelerated motion  and does that cause gravitational waves in the same way as em radiation  is caused?

I have been thinking about what happens when 2  objects come close to each other and  their motion is changed by ,eg electric repulsion. 

It seemed to me that there might also(in addition to the em wave)  be a gravitational wave as a result of the acceleration. 

 

 

[joigus]

No. Gravitational waves any sizeable would only be produced by extremely violent astrophysical processes, like BH collisions or the Big Bang.

There is something called gravitomagnetism in which gravitational waves are included, but also includes other gravitomagnetic phenomena, like frame dragging. Maybe that's what you have in mind.

[geordief]

10 minutes ago, joigus said:

No. Gravitational waves any sizeable would only be produced by extremely violent astrophysical processes, like BH collisions or the Big Bang.

There is something called gravitomagnetism in which gravitational waves are included, but also includes other gravitomagnetic phenomena, like frame dragging. Maybe that's what you have in mind.

No(now I am just imagining this)

I thought perhaps that the huge number of tiny accelerations within  the Earth ,and over the length of time the Earth has existed  might  perhaps add up to some overall  effect.

 

[zapatos]

34 minutes ago, joigus said:

No. Gravitational waves any sizeable would only be produced by extremely violent astrophysical processes, like BH collisions or the Big Bang.

 

Is there some threshold above which gravitational waves will be created? Or do small objects, say a couple of asteroids colliding, create gravitational waves that are just too minuscule to measure?

Edited March 20, 2023 by zapatos

[joigus]

34 minutes ago, zapatos said:

Is there some threshold above which gravitational waves will be created? Or do small objects, say a couple of asteroids colliding, create gravitational waves that are just too minuscule to measure?

They would be there, but be too minuscule to measure. That's one of the reasons why LIGO was such a challenge.

[swansont]

No threshold (unless there is one from quantum gravity), but smaller masses and accelerations would give smaller amplitudes, and gravitational radiation requires a change in the quadrupole moment - not all accelerations will result in radiation

[geordief]

1 hour ago, swansont said:

not all accelerations will result in radiation

Do they have any gravitational  effect at all?

I thought acceleration  and gravity were more or less the same thing.

[Genady]

9 minutes ago, geordief said:

I thought acceleration  and gravity were more or less the same thing.

But they are not the same. Gravity is spacetime curvature. Acceleration is not.

[geordief]

22 minutes ago, Genady said:

But they are not the same. Gravity is spacetime curvature. Acceleration is not.

Does acceleration cause spacetime curvature?(it seems to cause gravitational  radiation and doesn't the equivalence theory say that scceleration is indistinguishable  from gravity except for tidal forces?)

Edited March 20, 2023 by geordief

[Genady]

1 minute ago, geordief said:

Does acceleration cause spacetime curvature?

Acceleration of an observer or of a frame of reference does not cause spacetime curvature.

5 minutes ago, geordief said:

except for tidal forces

Tidal forces are manifestation of curvature.

[geordief]

4 minutes ago, Genady said:

Acceleration of an observer or of a frame of reference does not cause spacetime curvature.

Well spacetime curvature is just a model isn't it?Can't an accelerated  frame of reference  show spacetime as curved also?

 

(Stop me if I am talking rubbish -I normally am)

Edited March 20, 2023 by geordief

[Genady]

Just now, geordief said:

Can't an accelerated  frame of reference  of reference show spacetime as curved also?

It cannot.

[geordief]

Just now, Genady said:

It cannot.

Thanks. 

[joigus]

27 minutes ago, geordief said:

Can't an accelerated  frame of reference  show spacetime as curved also?

 

Curvature is frame-independent. If there is curvature in one frame, there is curvature in every frame. By going to a reference frame that compensates for that acceleration, you would go back to an inertial frame.

[geordief]

2 minutes ago, joigus said:

Curvature is frame-independent. If there is curvature in one frame, there is curvature in every frame. By going to a reference frame that compensates for that acceleration, you would go back to an inertial frame.

Thanks again.

[swansont]

2 hours ago, geordief said:

Do they have any gravitational  effect at all?

I thought acceleration  and gravity were more or less the same thing.

We’re talking about the emission of gravitational waves, not the equivalence principle 

I think it wouldn’t matter how the acceleration came about, but you need the gravitational field in place in order to perturb it to emit the waves.

[geordief]

35 minutes ago, swansont said:

We’re talking about the emission of gravitational waves, not the equivalence principle 

Does "Einstein's sealed  room" cause gravitational waves if the acceleration is strong enough?

 

I had thought all acceleration produced gravitational  radiation but you said a while back  in this thread this was not the case  and a "change in the quadrupole  moment  was required"

 

Could you explain a little further about that? (or would it be  easyish  for me to look that up on google?)

[swansont]

A spherical mass ( i.e. a monopole) rotating or undergoing an acceleration in some direction will not emit gravitational waves.

The quadropole moment measures how much a sphere is flattened

https://van.physics.illinois.edu/ask/listing/204

[geordief]

1 minute ago, swansont said:

A spherical mass ( i.e. a monopole) rotating or undergoing an acceleration in some direction will not emit gravitational waves.

The quadropole moment measures how much a sphere is flattened

https://van.physics.illinois.edu/ask/listing/204

So ,if there  are very small accelerations in a system  which do not produce gravitational  waves do they have any  gravitational effect at all ?

I understand that in the frame of the accelerated objects  acceleration is indistinguishable  from gravity - but (as per @joigus) this is not a  frame independent effect.

 

So can I take it that there are no gravity related effects from any accelerated motion,specifically  that there is no effect on the gravity field?

[Genady]

10 minutes ago, geordief said:

in the frame of the accelerated objects  acceleration is indistinguishable  from gravity

This is incorrect. No tidal forces - no gravity. And vice versa.

[geordief]

12 minutes ago, Genady said:

This is incorrect. No tidal forces - no gravity. And vice versa.

That is true (apologies ) Is gravity a synonym for spacetime curvature?

Suppose a system was accelerated at one point  rather than uniformly ,would that create tidal forces?

 

Suppose Einstein's sealed box was accelerated at the one point would that cause the box to break up in the same way as tidal forces  would break it up or strain it?

Edited March 20, 2023 by geordief

[Genady]

13 minutes ago, geordief said:

That is true (apologies ) Is gravity a synonym for spacetime curvature?

Suppose a system was accelerated at one point  rather than uniformly ,would that create tidal forces?

 

Suppose Einstein's sealed box was accelerated at the one point would that cause the box to break up in the same way as tidal forces  would break it up or strain it?

Gravity is synonym of spacetime being curved. No matter how creatively system moves, it will not curve spacetime and will not simulate gravitational tidal forces.

[geordief]

1 minute ago, Genady said:

Gravity is synonym of spacetime being curved. No matter how creatively system moves, it will not curve spacetime and will not simulate gravitational tidal forces.

Why is it called the equivalence principle if gravity and acceleration are not equivalent?

Is there some other equivalence  ,or some aspect of the relationship btw the two phenomena that is being referred to?

Is it possibly the equivalence btw the acceleration caused by gravity and the inertia involved in accelerating mass?

[Genady]

8 minutes ago, geordief said:

Why is it called the equivalence principle if gravity and acceleration are not equivalent?

Is there some other equivalence  ,or some aspect of the relationship btw the two phenomena that is being referred to?

Is it possibly the equivalence btw the acceleration caused by gravity and the inertia involved in accelerating mass?

Gravity and acceleration are indistinguishable in a system which is infinitesimally small in space and time.

[geordief]

15 minutes ago, Genady said:

Gravity and acceleration are indistinguishable in a system which is infinitesimally small in space and time.

Perhaps irrelevant but did Einstein state this or did he perhaps just state that they were indistinguishable with the qualification coming some time later?

(I have heard that General Relativity has advanced a lot since his time ,even as his predictions still to this day  keep getting shown to be correct  as in gravity wave detection and hopefully gravitons one day)

 

Edited March 21, 2023 by geordief