sci.physics.relativity

Let's say there are small magnets enclosed in plastic structures such
that each magnet is free to rotate within this structure. And let
these plastic structures be in the vicinity of a very strong magnet.
These magnets within these plastic structures will align with the very
strong magnet. We can change the orientation of the plastic
structures and the magnets contained therein will remain aligned to
the very strong magnet.

Now if we have huge number of these structures, randomly positioned in
space, in each local region of space we observe, we will only see a
force of attraction between adjacent magnets. But we know magnets both
attract and repel. If we look at larger volumes of space, we will see
repelling as well as attraction between the magnets. As the magnets in
this space orient themselves to one another, the outer reaches of this
space will be the regions where repelling is most evident, eventhough
each local.

The question I have is the following. If we hypothesize that the
nucleus of an atom can change its orientation relative to the chemical
structure of compounds, then what is the definitive experiment that
leads all physicists to believe that gravity is only an attractive
force and repelling due to gravity doesn't exist?

I know that its called a Law of Attraction, and not a hypothesis of
attraction, but I don't see why modern day astronomical observations
of accelerating objects aren't really observations of repelling due to
gravity instead of due to hypothetical things like the big bang, dark
matter, dark energy, etc.

Thanks,
David Seppala