A daydream the other day led me to the question if "a universe filled with water (or any other substance for that matter), instead of being mostly void" could exist within the rules of our current one.
I set on a Google journey to try to figure things out myself but I quickly hit the upper boundaries of my understanding of physics.
Now I am well aware that after a certain point, objects collapse under the force of their own gravitational field. Also something something about the Schwarzschild radius and 3 solar masses.
Extended to infinity and relative to its radius, the mass of the object has a cubical growth rate, while the force of gravity drops off at a square rate (does Newton's law of gravitation apply here?). Clearly the extra mass should overpower the gravitational decay, ultimately leading to a collapse.
I presume all this has to do with all points inside the object being attracted to each other and that there is a center of the mass.
This is where the original question kicks in - what if the object was so ridiculously big, or even better - infinitely big, that there was no single center of mass.
Would a "structure" like that hold? Will another object floating inside experience weightlessness as it is being pulled with an equal force from every direction? What weird relativistic effects would arise from the fact that even if the pull cancels out, it still exerts an infinite force?