Occam's Universe:The Biphasic Universe
The series of cosmological models initiated by and based on the theory of general relativity depict expanding or alternately expanding and contracting Universes.
But need the Universe in every part of it be either entirely expanding or contracting?
That is, may not some regions of the Universe be expanding and others contracting?
Given such variation, will not expanding regions be dropping in potential energy with regard to all particles and mass (and even photons) in them, as does quantum mechanics' "particle in a box" system, and contracting ones increasing? (The implicit assumption that expansion or contraction does not result in an expansion or contraction of those particles as well, leaving all as before, at least relatively, is shared by those models.)
And will not particles be inclined to stay in or travel to expanding regions with their lower, and be expelled from contracting ones with their higher, potential energies?
Call the former condition "gravity", and the latter "antigravity".
It might be objected that gravity is associated with particles (and photons, for that matter), but gravity, like electrical and magnetic attractions and repulsions, at least on the finest scale, is an extensive relation, not an intensive property.
It is not proof of this hypothesis (see the fallacy of affirming the consequent), but deep imaging and mapping of our Local Universe shows that it is apparenly biphasic, one phase—call it "Wall"—consisting of galactic superclusters in filaments and walls, all interconnected, the other phase—call it "Void"—consisting of nothing observable, and apparently not affecting imaging of Wall beyond it, and likewise interconnected; our Local Universe therefore presenting on the whole a somewhat spongiform structure.
Given Wall and Void, could the repulsion and even acceleration of particles and even photons from Void and consequent carriage of momentum from Void into Wall do away with the need for invocations of or be an alternative interpretation of "dark matter" and "dark energy"?
And could the end of contraction on the finest scale in Void result in particle-production, such particles quickly accelerated out of Void into Wall, as cosmic rays?
As a final wild speculation, while it is attractive to contemplate expansion and contraction as complementary, biphasic structure is found not only in intrinsically-biphasic systems but also in many systems changing in energy or through which energy is flowing, suggesting the possibility that our Local Universe as a whole may even in the hypothesized case still exhibit a net expansion.