Here is my short answer ......
" Where two objects are in close proximity they shield each other from part of the pressure " and since to work on all normal physical levels this pressure must therefore be able to be blocked by both large objects and small. Consider 2 dust motes in space, at some distance from any other significant bodies, but close to each other. Gravity dictates that they will be attracted to each other and will eventually touch ... so for pressure to function in the same way even a dust mote is able to block this pressure to some degree so that they move towards each other by it's tiny blocking of the pressure.
Therefore if we build a solid box, such that it's interior cavity is enclosed in every direction by pressure blocking mass, and place a marble in it, as the pressure has been uniformly blocked in every direction there should be no pressure remaining at all inside, and the marble should be free to float around regardless of any other external pushing or attractive forces.
Here is my long answer ......
I applaud your hypothesising here Alex, very interesting. In terms of assuming that a convention, ie gravity, may in fact be truly caused by another force working in a different or even reverse direction has both merit and precedent.
Everyone knows that the "conventional" flow of electricity dictates that electricity flows from positive to negative, but anyone who has studied any electrical theory at all knows that the actual flow of electrons (negatively charged particles) actually flows from negative to positive.
(I would also love to launch into my own personal fave here - light bulbs do NOT emit light, they suck dark - but another time perhaps.)
Anyway keeping an open mind - remember, a
truly open mind is one that is prepared to forgo ANY conclusion in support of new evidence - lets say that your hypothesis of Universal Pressure for want of a better name still appears to fit all known observations and results as the theory of Gravity, we need to then see if we can find a case in which your new theory either describes some factor of "gravity" better, or if both hypotheses seem to fulfill and explain all known and observed "symptoms" equally then we need to design an experiment of some sort that will allow us to differentiate whether gravitational attraction, or universal pressure, is the true cause.
Does your hypothesis then firstly explain all known attributes of "gravity"? Lets say for the moment that it does (I may come back to this later - it IS well after 3am and I may come up with other thoughts here yet when I'm not hallucinating, and when this green octopus stops bothering me ...... yes yes ok, I will tell him later, leave me alone!)
Anyway ..... so assuming that both hypotheses seem to fit the bill, we then need to devise a test to determine if the universe really DOES push, or whether gravity really does suck (as I've long suspected after falling from a very tall tree as a child). What we would need to do perhaps is to build some form of shielding device wich woudl either block the stream of universal particles, or to block the force of gravitational attraction. If we can devise a method of blocking either one, but not the other, we have proved that the blockable force must exist - you cannot block something that does not exist!
I think to give some of the rest of the class a fair go I'll leave this rather mentally stimulating conversation there for now, and I'll go read up on E.E. "Doc" Smiths Skylark series of books, etc - I seem to recall frequent use of Q beams and Z shields (or vice versa - the point is the Q or Z shield was inpenetrable to any "etheric" force, and his definition of the all pervading ether had some interestingly similar tones to your universe wide particle pressure.)
