Could the Earth be hollow?

[junior06]

In response to 'pzkpfw', Post 11. I fully understand this explanation of how pressure increases the closer you get to the 'Y' of the model.It is very probable that I will have to accept that the enormous pressures present in the interiors of any planet or star will be enough to negate the effects of gravity and therefore the possibility of the presence of any central void. It is relevant to mention at this juncture that the initial proposal of there perhaps being a void at the centre of any massive celestial sphere,( as so proposed at the start of this thread), was intended to be more an excercise in mental gymnastics,( specifically in relation to the effect of gravity within the interior of said sphere), as opposed to being a definitive proposal which challenged mainstream theories.Continuing in that vein therefore,your '123456789Yabcdefghi' model,is correct when applied to a sphere which is has a solid core.The model however, does not apply to a sphere which has a supposed void at centre.( Given also that supposed theoretical said void could have a diameter of at least many 100's,if not 1,000's of kilometers).The question arises of when, in the formation of a planet, does a central void begin to develop? The only answer which seems legitimate is when the increasing internal friction created from the accumulating pressure exerted by the matter which is being added to the fledgling mass of the planet, starts to turn the interior into molten magma.This, in combination with the centrifugal force of the rotation of the planet, could initiate the formation of the central void. Early massive volcanoes would further purge this central magma and would create the subsequent layers which would later dictate the subsequent composition of the adult planet,( crust, mantle, outer core etc.). Also,with regard to post 10.
'It seems to me that the answer to this question relies on an equation which takes into consideration 1. The force of gravity of the mass of the Earth 'pulling' at the centre. Versus 2. The amount of 'squeeze' pressure exerted on the core by that same mass. ...
1. Will become zero.
2. Will become very large.
With great respect, this does not strike me as being much of a definitive equation.

[pzkpfw]

In response to 'pzkpfw', Post 11. I fully understand this explanation of how pressure increases the closer you get to the 'Y' of the model.It is very probable that I will have to accept that the enormous pressures present in the interiors of any planet or star will be enough to negate the effects of gravity and therefore the possibility of the presence of any central void. ....

I think it becomes very important for you to clearly define what you mean by "effects of gravity" in "enough to negate the effects of gravity".

What is this "effect" that you think needs to be "negated"?

... With great respect, this does not strike me as being much of a definitive equation.

Well, no less definitive than:

... when the increasing internal friction created from the accumulating pressure exerted by the matter which is being added to the fledgling mass of the planet, starts to turn the interior into molten magma.This, in combination with the centrifugal force of the rotation of the planet, could initiate the formation of the central void. Early massive volcanoes would further purge this central magma and would create the subsequent layers which would later dictate the subsequent composition of the adult planet,( crust, mantle, outer core etc.).

I'm also not the only person who has answered "no" to your question, you could deal with some of the other objections too.



(It would also help if you could learn how to use quote tags - [quote=who wrote it] some text [/quote] - so that when you refer to posts it is clear who wrote what. In your previous post you make it look like some of your text that I quoted, was instead written by me.)

[WayneFrancis]

I don't know the exact depth of maximal gravitational force, but it has to be deeper.

Using numbers from this page, the core amounts to 32.5% of the Earth's mass and 54.6% of the radius, which works out to a gravitational acceleration at the mantle/core boundary of 1.09 g (ie., 9% greater than at the surface).

Even under the deliberately unreasonable assumption that the entire mass of the planet resides below 11 km under the surface, the acceleration at that depth would be only ~1.003 g.

You are right...Like I said I was going off of my, crappy, memory
We had this talk before in center of gravity for the planet earth/core of the earth

[WayneFrancis]

Yeah, the OP's already noted that. But I think the "important" part of it is that each layer has a consistent-enough density.

You note where the highest gravity is, but where is the lowest - and why?

the lowest gravity is at a distance of ~∞ because it is past an event horizon where the gravitational influence of the Earth is well...beyond the even horizon :P
I was being pedantic and wasn't actually criticizing your answer ....I was just being OCD.

[WayneFrancis]

In response to 'pzkpfw', Post 11. I fully understand this explanation of how pressure increases the closer you get to the 'Y' of the model.It is very probable that I will have to accept that the enormous pressures present in the interiors of any planet or star will be enough to negate the effects of gravity and therefore the possibility of the presence of any central void. It is relevant to mention at this juncture that the initial proposal of there perhaps being a void at the centre of any massive celestial sphere,( as so proposed at the start of this thread), was intended to be more an excercise in mental gymnastics,( specifically in relation to the effect of gravity within the interior of said sphere), as opposed to being a definitive proposal which challenged mainstream theories.Continuing in that vein therefore,your '123456789Yabcdefghi' model,is correct when applied to a sphere which is has a solid core.The model however, does not apply to a sphere which has a supposed void at centre.( Given also that supposed theoretical said void could have a diameter of at least many 100's,if not 1,000's of kilometers).The question arises of when, in the formation of a planet, does a central void begin to develop? The only answer which seems legitimate is when the increasing internal friction created from the accumulating pressure exerted by the matter which is being added to the fledgling mass of the planet, starts to turn the interior into molten magma.This, in combination with the centrifugal force of the rotation of the planet, could initiate the formation of the central void. Early massive volcanoes would further purge this central magma and would create the subsequent layers which would later dictate the subsequent composition of the adult planet,( crust, mantle, outer core etc.). Also,with regard to post 10.
'It seems to me that the answer to this question relies on an equation which takes into consideration 1. The force of gravity of the mass of the Earth 'pulling' at the centre. Versus 2. The amount of 'squeeze' pressure exerted on the core by that same mass. ...
1. Will become zero.
2. Will become very large.
With great respect, this does not strike me as being much of a definitive equation.

Something you seem to be confused about is just because the net gravity is 0 doesn't mean there isn't any gravity and more important that doesn't mean you are not in a gravity well. By the nature of a gravity well the bottom of the gravity well has a local net gravity of zero. But because the the Earth is not alone in the universe if you where at the centre of the Earth you'd still feel gravity. It is just that it would be the gravity of the sun you would feel.

Think of it like skiing down a mountain. At the top and the bottom the slope is very gentle you don't go very fast. Where the slope is larger you would go faster. But at the end of the day you are going to go down hill. Centrifugal force isn't going to help much at the centre of the Earth because the speed at which the core rotates is VERY slow so has very little centrifugal force exerted on it. In practical terms any body that had enough spin to cause a "hollow" centre would have a spin rate large enough to rip the object apart. IE it would be > then the escape velocity of that point in space.

[Grey]

We had this talk before in center of gravity for the planet earth/core of the earth

Junior06, it seems like you may have a similar misconception to hypergreatthing in this other thread, that there's a balance point somewhere away from the center of the Earth, so that the forces would tend to naturally cause a hollow to form at the center. That's not the case; the forces of gravity and pressure both work together to try to compact any large object into a solid sphere. There's a slight deformation from the rotation of the planet, but that's only about 0.3%.

[Strange]

It is very probable that I will have to accept that the enormous pressures present in the interiors of any planet or star will be enough to negate the effects of gravity and therefore the possibility of the presence of any central void.

I also don't quite see what "effects of gravity" you think would need to be negated. Even if you ignore the pressure (imagine a hollow tube through the center of the sphere) the gravity will be zero at the centre; i.e. there is nothing to push you away from the centre. In fact, if you started to drift away from the center, then the gravitational force would increase and push you back to the center. So even without pressure, it would seem that the center is still the only stable place for mass to accumulate.

[a1call]

*- Is a hollow sphere a stable configuration in absence of external forces? Can internal pressure of some gas be in equilibrium against the gravitational forces of loose-solids/liquids around the gas (at least for some lower masses like a soap bubble)?

ETA: *- How thick can the shell of a soap bubble get in absence of external gravity (or micro gravity) but in presence of external pressure?

[cjameshuff]

Centrifugal force isn't going to help much at the centre of the Earth because the speed at which the core rotates is VERY slow so has very little centrifugal force exerted on it. In practical terms any body that had enough spin to cause a "hollow" centre would have a spin rate large enough to rip the object apart. IE it would be > then the escape velocity of that point in space.

Only orbital velocity, not escape velocity. But yeah, the result would still be an accretion ring, not a planet with a hollow core.

*- Is a hollow sphere a stable configuration in absence of external forces? Can internal pressure of some gas be in equilibrium against the gravitational forces of loose-solids/liquids around the gas (at least for some lower masses like a soap bubble)?

On a planet-like body where the strength of the shell is not a factor, only if the gas is higher density. Sulfur hexafluoride gas with a mantle of aerogel? Obviously, a balloon or compressed air tank is a stable configuration, and you could build brick sphere that could contain non-zero interior pressure, but these rely on material strength to hold their shape.

Again, you can ignore the gravitational force of the enclosing shells for the interior of those shells, but you can't ignore that those outer shells are being pulled inward by the matter in their interior. Each shell is in equilibrium between gravitational force pulling it inward, pressure from outer shells pushing it down toward the core, and pressure from inner shells pushing it outward. The gravitational force on any given shell becomes smaller as you approach the core, but it adds to the pressure transmitted to lower shells, which steadily becomes higher as you approach the core. The walls of a void would have the weight of a planet pushing them inward even if they didn't have any gravitational force pulling them toward the center.

The answer is not that the void doesn't form because gravity is "negated" by pressure. It's quite the opposite...that pressure results from gravity, a big ball of stuff piling up in its own gravity well. The formation of a void isn't opposed by something negating gravity, it would require that gravity be negated by something else.

[a1call]

In the ISS video that I linked to earlier, what would happen if instead of an Alka-Seltzer, a straw was inserted to the middle of the water sphere and a small air bubble was gently blown in? Would the air bubble exit the water sphere or remain at the center?

[cjameshuff]

In the ISS video that I linked to earlier, what would happen if instead of an Alka-Seltzer, a straw was inserted to the middle of the water sphere and a small air bubble was gently blown in? Would the air bubble exit the water sphere or remain at the center?

There would be no force pushing the air bubble toward the surface of the sphere (aside from an extremely weak buoyancy force from the water blob's own gravitation), but if it wandered close enough, it'd almost certainly form a bubble with the usual wall thickness (determined by the same molecular kinetics that cause surface tension) on the surface of the water sphere.

[a1call]

There would be no force pushing the air bubble toward the surface of the sphere (aside from an extremely weak buoyancy force from the water blob's own gravitation)

What if the blob was more massive, say 100 cubic meters. Would the air bubble rise/sink to the surface of the blob then?

[a1call]

ED-100-A..jpgED-110-A..jpg

I can't be sure, but I think there are situations were a hollow sphere would be a stable configuration.

Warning: Buckyballs can be very dangerous even fatal if swallowed and are not for children.

I recently bought some. It is not that difficult to arrange the magnetic balls in hollow shapes. Now, since each ball is polarized the attraction between the adjacent balls is stronger than across the void. But all balls do attract each other to some extent. It is important not to use intuition to predict such void behavior. I suspect it might be possible to have hollow configurations where gravitational attractions by close by matter would surpass the attractions across the void (not vacuum) due to the inverse square law. This, perhaps would make a hollow sphere stable under certain conditions.

[Strange]

I would have thought a hollow sphere of solid material would be stable if it had enough compressive strength to balance the gravitational force - it is really just two domes back to back (admittedly a spherical dome isn't the strongest shape, but they will support thier own weight). A bubble will be stable if its surface tension matches the pressure inside (plus gravity if it is massive enough).

But, it cannot arise naturally (well except in some very special circumstances*). And if perturbed it will collapse to a ball of rubble (with no hole in the middle).

(*) Some great examples here: http://en.wikipedia.org/wiki/Natural_arch

[R.A.F.]

...I think there are situations were a hollow sphere would be a stable configuration.

That might be true, but the topic of this thread, a hollow Earth, would not be one of those configurations.

[a1call]

That might be true, but the topic of this thread, a hollow Earth, would not be one of those configurations.

Agreed, since as mentioned by others there is evidence to the contrary. However IMHO a hollow sphere is still related to the topic. It is important to express that though Earth is not hollow, hollow spheres can exist in spite of gravitational forces in fluid materials (perhaps, and if indeed they can).

[eburacum45]

You could make a balloon out of steel and fill it with air; this balloon could be very much larger than the Earth. Then you could live on the outside, or perhaps sandwiched between two layers of the balloon.
Here's Dani Eder's analysis of a 'bubbleworld' filled with hydrogen; 240,000 km in radius. http://yarchive.net/space/exotic/bubbleworld.html

[cjameshuff]

What if the blob was more massive, say 100 cubic meters. Would the air bubble rise/sink to the surface of the blob then?

The buoyancy forces from the water's own gravitational field would be stronger.

I can't be sure, but I think there are situations were a hollow sphere would be a stable configuration.

Of course. There are many situations where gravity is not the dominant force, and this can occur.

I recently bought some. It is not that difficult to arrange the magnetic balls in hollow shapes. Now, since each ball is polarized the attraction between the adjacent balls is stronger than across the void. But all balls do attract each other to some extent. It is important not to use intuition to predict such void behavior. I suspect it might be possible to have hollow configurations where gravitational attractions by close by matter would surpass the attractions across the void (not vacuum) due to the inverse square law. This, perhaps would make a hollow sphere stable under certain conditions.

Those are just spherical magnets. They do not all attract each other (in some orientations they have no net force, and in others they repel each other), and they do not interact by an inverse square force (they are dipoles, and their far field falls off with the cube of distance). They do not act like gravitating matter, and nothing you do with them has any resemblance to how planetary formation occurs.

[PetersCreek]

It is relevant to mention at this juncture that the initial proposal of there perhaps being a void at the centre of any massive celestial sphere,( as so proposed at the start of this thread), was intended to be more an excercise in mental gymnastics,( specifically in relation to the effect of gravity within the interior of said sphere), as opposed to being a definitive proposal which challenged mainstream theories.

junior06,

I remind you...again...that the Q&A forum is where one comes to get mainstream answers to questions. This is not the place speculate, spitball, or engage in mental gymnastics with an ATM idea. Since mainstream answers has been given and you seem intent on continuing your ATM speculation, this thread is closed. If you wish to defend your idea in the ATM forum, in accordance with the rules of that forum, you may post it there.

If anyone involved in the side discussions wishes to have posts moved to a thread in a more appropriate forum, please report this post.