MovingTarget said:

It doesnt make sense to me, the only reason the marbles will roll towards the bigger marbles on this blanket is because theres already gravity pulling the bigger marble down into the blanket,

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Alan Stone said:

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See the post above by hendostan.

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I'm saying the marble wouldn't be influenced by the dent unless there were gravity to make it adhere to the blanket in the first place. It would just continue on at the same height it was before it reached the rim of the dent. Likewise, the dent wouldn't be produced without gravity.

Regardless of the underlying studies, I think it's a rather ill-conceived analogy. It doesn't explain gravity without using gravity, which is circular logic. What's more, if those dents are in 4D, a blanket with a 3D object on it doesn't really cut it for comparison purposes.

I'm still interested in the theory though. If those dents in space-time exist, what causes them? And how are they dents, into which dimension? If it works anything like the blanket-marble example (in which the 2D blanket is dented into a third dimension), the dents would have to be in a fourth spatial dimension, right?

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I'm saying the marble wouldn't be influenced by the dent unless there were gravity to make it adhere to the blanket in the first place. It would just continue on at the same height it was before it reached the rim of the dent. Likewise, the dent wouldn't be produced without gravity.
Regardless of the underlying studies, I think it's a rather ill-conceived analogy. It doesn't explain gravity without using gravity, which is circular logic. What's more, if those dents are in 4D, a blanket with a 3D object on it doesn't really cut it for comparison purposes.
I'm still interested in the theory though. If those dents in space-time exist, what causes them? And how are they dents, into which dimension? If it works anything like the blanket-marble example (in which the 2D blanket is dented into a third dimension), the dents would have to be in a fourth spatial dimension, right? 

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I guess I should clear up my analogy.  The dents are not caused by gravity, they are an inherent characteristic of the universe, they CAUSE gravity.  When you think about this analogy, forget about what you know about 'gravity'.  The marbles stick to the blanket because everything is 'stuck' to the fabric of spacetime. The dents are in all four dimentions.

Don't try to stretch it literally to 4 dimentions, the point of the analogy is it makes the theory of gravity simple enough to understand.  Research it yourself if you don;t understand, but it is what you will be taught in any physics course.

As for what causes the dents, there is plenty of speculation, but we don't truly know.  I think this question is a little like 'what causes the universe?" 

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  Maybe i shoudl have re phrased my sentence to say "the mass of an object, such as a ball, compared to that of a boulder, has no bearing on the RATE at which an object falls within a system."

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I didnt think your blanket analogy worked for the type of Question GOMP asked. HE thought that vacuum's made the idea of gravity worthless.... this was my understanding anyway... Thats why i said what i did above.

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I wasn't replying directly to Gomp, but to another post, but anyway I thought he was asking through what mechanism gravity works through a vacuum.  Sorry if i didn't help you any Gomp!