Gravity Question

[Stumblebum]

This is all hypothetical and probably never happens this way.

 

I'm trying to picture a particle that occupies the very centre of gravity for a planet for instance. Is that little particle generating the gravitational pull that is holding the planet together? Why isn't that particle pulled away from the centre by the surrounding mass? Could gravity be pulling in all directions within an object with mass? Seems as if mass doesn't do the attracting but its something else. Can someone clear this up for me? I know you guys/gals have come through before.

[J.C.MacSwell]

This is all hypothetical and probably never happens this way.

 

I'm trying to picture a particle that occupies the very centre of gravity for a planet for instance. Is that little particle generating the gravitational pull that is holding the planet together? Why isn't that particle pulled away from the centre by the surrounding mass? Could gravity be pulling in all directions within an object with mass? Seems as if mass doesn't do the attracting but its something else. Can someone clear this up for me? I know you guys/gals have come through before.

 

In which direction do you think it should be pulled away?

[Stumblebum]

Forget about direction for a minute ... would that central particle be pulled by the surrounding material even though it would be equal in all directions or is the central particle's mass pulling everything around it together? How can this be? What is it that's causing everything to fall to the center? Can a particle make it to or actually exist at the center of a perfect sphere?

[BlackHole]

This is all hypothetical and probably never happens this way.

 

I'm trying to picture a particle that occupies the very centre of gravity for a planet for instance. Is that little particle generating the gravitational pull that is holding the planet together? Why isn't that particle pulled away from the centre by the surrounding mass? Could gravity be pulling in all directions within an object with mass? Seems as if mass doesn't do the attracting but its something else. Can someone clear this up for me? I know you guys/gals have come through before.

 

In QFT there was an experiment which demonstrated that two parallel laser beams do not interact which made me think that light doesn't really gravitate. On the other hand, two anti-parallel laser beams do interact (for some reason).

 

Maybe the answer lies in a vacuum theory, but others prefer dark energy, strings and so on.

[Stumblebum]

I would have to think that each subsequent layer of a sphere gets more massive as you work in from the outer layer. It just seems strange but I would have to think that each layer as you go towards center must have more particles than the layer outside of it. If the sphere is all of one material then the particles must shrink as you approach center because wouldn't the mass of the center have to be greater than whats around it? Help!!!!

[Spyman]

would that central particle be pulled by the surrounding material even though it would be equal in all directions

Yes, make a circle and calculate the sum of gravity for any position inside the circle, they will all have the same sum of gravity = zero.

 

When the position is closer to one wall that part of the wall pulling it will also be smaller and in the opposite direction the distanse is greater but there will be more part of the wall.

 

In a perfect circle You will find they exactly cancel out each other.

[J.C.MacSwell]

I would have to think that each subsequent layer of a sphere gets more massive as you work in from the outer layer. It just seems strange but I would have to think that each layer as you go towards center must have more particles than the layer outside of it. If the sphere is all of one material then the particles must shrink as you approach center because wouldn't the mass of the center have to be greater than whats around it? Help!!!!

 

The pressure is highest at the center.

 

The net gravitational force is lowest, goes to zero, at the center.

 

The center of an all one material sphere would be generally denser at the center as you describe The density gradient depends on the bulk/volume modulus of the material, temperature gradients and bulk coefficient of expansion with temperature and any phase changes involved.

 

The Earth is considerably denser at the center as the denser materials gravitate toward the center.

[swansont]

This is all hypothetical and probably never happens this way.

 

I'm trying to picture a particle that occupies the very centre of gravity for a planet for instance. Is that little particle generating the gravitational pull that is holding the planet together? Why isn't that particle pulled away from the centre by the surrounding mass? Could gravity be pulling in all directions within an object with mass? Seems as if mass doesn't do the attracting but its something else. Can someone clear this up for me? I know you guys/gals have come through before.

 

If the mass distribution is uniform, then mass outside of a given point does not contribute, as it all cancels. This is a consequence of Gauss's law. The only mass that contributes to the net force is inside the sphere.

[BlackHole]

Since the earth's center is also the center of mass, gravitation in the center should be zero (the forces cancell out).

 

However i believe gravity has something to do with the vacuum. If light (or any electromagnetic radiation) is not effected by gravitation then all we need is a vacuum theory.

[swansont]

However i believe gravity has something to do with the vacuum. If light (or any electromagnetic radiation) is not effected by gravitation then all we need is a vacuum theory.

 

But it has been demonstrated that gravity deflects light.

[BlackHole]

But it has been demonstrated that gravity deflects light.

 

I'm not sure that the equivalence principle holds true in all reference frames. From the equivalence principle we get the stress-energy tensor which states that energy gravitates.

[Stumblebum]

Does the exact center of gravity for a given mass actually contain a particle? If not is it an amount or quantity of spacetime thats trapped there?

[Spyman]

Where is the center of gravity for a hollow spherical body - In the center.

 

Is there a particle there - No, it's hollow.

 

Can there be a particle there - Yes, but it makes no difference.

 

Inside a hollow sphere there is no gravity force pulling particles to the center.

 

Thus nothing is necessarily "trapped" at/in the center of gravity.

[Stumblebum]

I was thinking a solid mass. When a black hole is formed what happens to the space between particles? Does it get squeezed out or does some get trapped? Is it not possible that some squeezed space could be trapped in the center?

[Spyman]

OK, take a solid perfectly formed spherical body and split it into different layers from the surface to the center. Now You can calculate the force of gravity for each layer and then add them togheter to get the total sum of gravity for the center.

 

For every layer the force will be zero thus total sum ends up zero.

 

Nobody knows whats happens to the space between particles when a BH is created, it's is not even known whats happens to the particles.

 

How do You squeeze a vacuum ?

 

It's possible to have empty bubbles inside a body, even in the center, but how to squeeze emptyness ?

 

There is pressure inside a body but the pressure is not caused directly by gravity itself, it's caused by the weight of the matter above. (Which is caused by gravity.)

 

The pressure will fill out holes if matter lets it, liquid, soft enough or in other ways. But if the hole is empty, nothing inside it will be squeezed.

 

If the matter is to rigid to let the pressure fill out the holes they will be trapped inside the matter, but not trapped by gravity.

 

If You take a perfectly empty closed box and squeeze it togheter, will the space inside the box get squeezed or will the walls of the box move inside space to get closer to each other ?

 

When You walk do You squeeze space in front of You and streach it behind ?

 

Is matter for always attached to a point in space or is it lose to move around inside space ?

[Stumblebum]

It's possible to have empty bubbles inside a body' date=' even in the center, but how to squeeze emptyness ?[/quote']

 

This is far fetched but lets say there is a pocket or pockets of empty space within a BH. As the BH collapses in on itself it will eventually be of less volme than the pocket of empty space it surrounds. It will have to fall into it.

 

Before this takes place the collapsing mass will have stretched spacetime to the point where there is no space surrounding it. Could it be possible that once the BH's volume is less than the pocket of compressed empty space contained within it that the mass which has now fallen into the empty space cannot collapse any longer(no more space to collapse into) and both empty space and mass start to expand either violently or otherwise.

 

My feeble attempt at explaining the birth of a universe. I'm no physicist but its fun to take a stab at stuff like this.

[Spyman]

My feeble attempt at explaining the birth of a universe. I'm no physicist but its fun to take a stab at stuff like this.

Maybe You should try to understand space and gravity, before creating universes...

(Fantasy is nice but unleashed it will create fiction instead of science.)

If You take a perfectly empty closed box and squeeze it togheter, will the space inside the box get squeezed or will the walls of the box move inside space to get closer to each other ?

Emptyness can not be squeezed, the walls moves inside space.

 

On the other hand spacetime can be compressed, so maybe You will find this thread interesting:

 

Big Bang Question http://www.scienceforums.net/forums/showthread.php?t=6233

[Stumblebum]

I wasn't referring to the spacetime between the walls but the spacetime between the particles that make up the box. Whether that makes a difference or not when matter is crushed under gravity's infkuence, I couldn't tell you. Thanks for replying.