The universe is ultimately, and completely, composed of a continuum of material atoms.
Which continuously interactive atoms expand and contract with locally transmitted inputs and emissions of energy/matter.
If a sealed sphere, such as a plastic balloon, is taken out into space from the pressures of the Earth’s atmosphere at its surface, it will progressively expand in volume in the lower external pressures experienced there.
This is due to the collective expansions of the contained gaseous atoms in the balloon in the decreasing pressures at these increasing altitudes.
No interatomic vacuum exists in the entire universe.
And no experimenter can isolate an absolute vacuum. This is because atoms in the internal surfaces of a metal apparatus at very low pressures liquidate and then evaporate to fill the space.
Roger Munday
Kinetic Atomic Theory of Gases
This theory states that the component atoms of any observed volume of matter are in continuous "kinetic" motion within an interatomic vacuum.
This "kinetic" theory is today replicated in all theoretical physics books and papers.
And evidently you all collectively accept this essentially vacuous theory of the ultimate structure of matter.
Even when it is experimentally proven that such nonmaterial, perfectly vacuous spaces cannot be isolated or created.
I suggest you go to a library and take out Henning Genz’s book “Nothingness – The science of empty space” in which he states:-
“The laws of physics will not admit the existence of a completely empty space.”
In other words, atoms are not separated by a hypothetical “vacuum”.
Roger Munday