Explaining gravity with gravity?

[Baby Astronaut]

As a curious thought, if gravity is really caused by an object causing a dimple in space, then wouldn't the act of lesser mass objects falling into that dimple be in itself gravity in action?

 

Do you see what I mean? Object falls in a hole = gravity. Smaller object falls into dimple around larger object = gravity.

 

So basically, aren't we using gravity to explain gravity?

[timo]

Yes. That's the main reason I don't like these kind of pictures "explaining" gravitational effect as a result of spacetime curvature. By that I mean pictures like this one:

 

"Understanding" this picture -in my opinion- heavily relies on the (knee-jerk) assumption that things have the tendency to fall down. However, from the mathematical standpoint it is only the geometry of the plane that determines motion on the plane. Hence, the picture is equally valid if you turn it upside down. The attached picture is the same one as above, just rotated by 180°. In my opinion, it is absolutely not clear from the visualization why the smaller peak (smaller object) should circle upwards to the larger peak (larger object) now. I think something is fishy with this rubber-plane visualization. I don't really know what, though.

 

As for the implication on science that these visualizations have: Practically none. When you do calculations you do not rely on terms like "dents in spacetime" but rather just calculate some properties of spacetime, apply some rather general criterion (path of an object is such that some quantity integrated over the path is minimal) that depends on these properties and get a result that coincides with the observed phenomena. No referal to gravity, there. Only the visualizations made seem to rely on our everyday-knowledge of Newtonian Gravity.

[Baby Astronaut]

I'm still trying to digest your answer.

 

But in the meantime, here's another curious thought. Your images are the type used to illustrate the gravity well by the coin rolling in the funnel you dropped a coin into. They claim gravity works similarly.

 

However, the coin would have to approach the funnel just right in order to avoid simply dropping right in immediately. And the coin doesn't remain at the same level each revolution -- it draws closer and closer.

 

So this presents some issues.

 

1. The dimple in space would have to be subtly widespread at the top, and over an enormous distance. That way, no matter how the coin approached, it would get a chance to slightly adjust its course to the slight decline leading to the center far away. Sometimes the coin approaches dead-on, and thus crashes into the hole much as space debris hits earth instead of being caught in its orbit.

 

2. The slingshot effect makes less sense, because a spacecraft would enter the dip, catch some acceleration, but then should lose that acceleration because in order to leave the dip, it would have to climb the same level of dip.

 

3. The dip means that whatever object caused it has displaced an amount of space. Maybe the space around the dip is now more compact, squeezed together. It's only logical since it has to go someplace. I'm not certain if that's what is referred to as "warping" of space, but if so, it would not be too far-fetched to imagine that space's properties would be affected somehow. For example, water being squeezed under pressure has a different freezing temperature. So maybe warped space has its differences too.

[granpa]

the idea of stretching space would make more sense in the case of like charges repelling. stretching space puts energy into it. overlapping 2 like charges doubles the field at every point which quadruples the energy. hence they would naturally repel. in that sense gravity is actually backward. thats why gravitational potential energy is considered negative.

[jjuris]

i love the gravity argument. My take is that everything in existence creates gravity, from the largest... to the smallest fundamentals that we dont know of yet. when we find out it should be a good time