Maybe I don't understand gravity (maybe no one does) but I can't get past the logic that the earth (and other suns and planets) must be hollow. If I'm standing at the exact center of the earth, the mass (which is what I understand creates gravity) is towards the surface and therefore should be pulling away from me at the center. At some point from the center it would balance out creating a hollow earth. The layers of molten lava would be pressed between the outer and inner surfaces by the force of the mass in the middle. I've never had anyone really explain why this wouldn't be true even though I've read a lot about the various "theories" of gravity. Before you say the centre is a solid iron core and that it's been proven because shock waves don't travel through it but around it - that would also be true if it were hollow. I'm not saying little green men live inside (although if they could travel across light years of space they could potenitally have the ability to pass through a solid) and I'm certainly not saying there is a sun inside like some people I've read (I guess they like light in their hollow earth) - just that logically gravity would pull outwards from the centre even not adding in the centrifugal force from the spinning.

Backroads

I don't see how logic fits in any of that paragraph.

Actually, this is a topic that I've never really thought about, yet makes complete sense to me. The only way that I could see your theory not working, would be if the earth isn't spinning fast enough to force the lava (molten core) to the outer edges of the center of the earth, to create the hollow core. It is an extremely interesting idea...and I think I'm going to check into it. Good luck with your post.

This part is true


and this is where it all goes wrong.

Place yourself at the exact centre of the Earth. Now move to your right away from the centre. There is now more of the Earth on your left than there is on your right. Gravity will try and pull you back towards the centre. Move up and there is greater mass below, again you are pulled towards the centre. It doesn't matter which direction you move away from the centre gravity will try and pull you back there. From this you should be able to see that the only place that gravity cancels out is in the exact centre and your reasoning behind the Earth being hollow is incorrect.

In fact if gravity had its way it would force objects into a tiny point at the dead centre, a singularity. This is what happens in a black hole. It is only because the strength of the material the Earth is made from is strong enough to resist the force of gravity that this doesn't happen (it's a lot more complicated than that but I don't think this thread is ready for discussion of the Swartzchild radius yet).

First I apologize for not understanding and I will look up Swartzchild radius to see what it's about. I still don't get the singularity part since it seems that gravity would cancel out at dead centre and be only incrementally stronger as you move out. With the spin of the earth would centrifical force not factor in (even though it would be pretty slow in the centre) And I'm not suggesting the earth is very hollow - only a little.

Firstly, backroads, welcome to the forum.

Why apologize? None of us know or understand everything so we all learn from putting out our ideas and seeing what others have to say.

This explains Centrifugal Force

and this explains Centripetal Force

So the body at the centre of the mass would not exhibit any centrifugal force unless it was acting on something preventing its progress in a straight line according to the objects velocity arising from the rotational acceleration (circular motion). I'm sure I could have explained that better but that's the gist of it.

The 'gravity increments' you refer to are true for different sized masses you can't apply incremental gravity in that way for a large mass.

Take the Earth for example. It has a huge mass and so the outer mass has this enormous gravity pulling it in to the centre. This applies great pressure to all the mass underneath so you still have the effect of the 'total mass gravity' applying through the whole mass. At least that's my understanding of how it works - someone else may be able to show that this is wrong or explain it a bit better.

Great explainatoin of Centrifugal force. But if the outside wall of the hollow part was what was restraining the object from moving further wouldn't it still apply? Your explaination of the normail theory is actually very good. I'm going to have to sleep on it to really get the picture in my mind. I can't get past thinking that once you start getting half way through that the pressure would in part start pulling the other way. It may not be enough to make it hollow, but not as dense as I see in the pictures of the solid core. It would put even more pressure though on the part between the surface and the middle. Thanks for your explainations. I'll ponder it some more....

I quite think that the idea hollow planets make sense...


http://www.bibliotecapleyades.net/tierra_h...ra_hueca_8a.htm

http://www.geocities.com/Area51/Shadowland...3/under012.html

http://www.theedgeam.com/guests/pastguest1.htm