Why is gravity unstable in 4D and can it be modified?

[Gold Barz]

I know that gravity can be extended to 4D but the conclusion always seem to be unstable, is the reason why they come up with unstable orbits and atoms is because they take how gravity acts here in 3D physics and apply it the same way to 4D physics? How about modificating the model? but we just don't know what kind of modifications can be made so we don't make any modifications...is this even remotely correct?

Is there no way that a isotropic 4D gravity model can become stable?

I might even suggest something even more wackier, like might there be new forms of matter in 4D physics, I would think that there would be a significant effect to elementary particles.

 

[Gold Barz]

Who else feels that we can't just extend basic mathematical equations to 4D models?...

 

[ahrkron]

Why are you so much interested in 4D models? They are not physical, unless you assume (a-la strings) that one of them is small or unobservable.

What need is there for that? In String Theory, the formalism requires the extra dimensions to work properly. In your case, why would you prefer to work with one extra dimension?