Can gravity be better described as buoyancy in spacetime than a pulling force? Lately I've been contemplating this analogy to better explain the phenomena we call gravity to my children.  Since I'm not a physicist or a mathematician, I'd like some input on the validity of my analogy.
Consider that a helium filled balloon will move from a high atmospheric pressure to a lower one.  The medium in which the balloon seeks equilibrium is our atmosphere, a.k.a. air.
Just for the analogy, if we consider spacetime as a similar medium to air, we can explain that the presence of matter in this medium will create a low-pressure situation in the spacetime in which that matter exists.  Therefore, it's easy to see how gravity is really a buoyancy effect on matter in the medium of spacetime.  It seems like a loop in causality, since the presence of matter is what causes the low-pressure in spacetime which then causes nearby matter to be pushed by spacetime via buoyancy towards the center of the low-pressure depression.
This may seem trivial but I've always had a problem with gravity being described as a pulling force.  I like to think of it as the result of spacetime density when matter is present.
To extend the analogy, I think the idea of spacetime having varying density can also explain how what we call gravity waves exist.  Waves in air (sound waves) are the compression and decompression of air moving out in all directions from its point of origin.  Gravity waves have this same effect on spacetime.  Spacetime is compressed and decompressed in a wave pattern that travels out from the point of origin.  So, shouldn't these gravity waves be called spacetime waves?
Does this compute?
 A: The problem is that you are thinking of spacetime as a physical object. In effect you have reinvented the idea of the aether. Apart from the fact there is no experimental evidence for this, an aether would pick out a preferred reference frame and contradict the basic principles of relativity.
Incidentally, and on the slightly nit picking front, be careful to distinguish between gravity waves and gravitational waves. The latter are the oscillations in the spacetime geometry recently detected by LIGO.
A: Well not to discourage from thinking about creative ideas, I would point a flaw with your reasoning.
First, what would make the matter to cause lower pressure of the "medium of space"?
Secondly, suppose even if your mechanism is true, then the force of gravity would be equal to 
(Normal pressure of the "medium of space") minus (Reduced pressure of the "medium of space")
The reduced pressure of the "medium of space" can reduce till it disappears altogether, means it would drop to zero.
That means, there would be an upper limit on the force of gravity when the reduced pressure becomes zero (supposing it does drop to zero, say at an event horizon of a black hole). 
That upper limit would be the normal pressure of the "medium of space".
As the force of gravity approaches infinite near an event horizon, that does not fit well with your idea unless the normal pressure of the "medium of space" is itself infinite. That would crush matter anywhere in space.
Keep thinking though.You know what to tell your children as you know their age and grasping capability.
