Observational evidence of accelerating expansion is explained by repelling dark energy ... Observe that we see such repelling energy as microwave background - corresponding to EM degrees of freedom of vacuum are thermalized to 2.725K noise - according to Wikipedia, this energy density gives 6*10^-5 of energy of our Universe ... ... but there are also other interactions, which are much more difficult to directly observe in analogous way - gravitational, weak, strong - they also have corresponding degrees of freedom - their interaction with EM is very weak, but there was billions of years to thermalize these degrees of freedom (to 2.725K) - couldn't it be what they call dark energy? Some of these degrees of freedom could interact weaker, such that in practice they are thermalized only in relatively active regions like galaxies, causing larger density of such energy there ... couldn't it be what is interpreted as dark matter? What is wrong with such simple and natural dark energy/matter candidates? We cannot directly observe any dark matter, it should accumulate in centers of stars and so have essential influence on their evolution ... If dark energy/matter are just thermal noise, their energy density will decrease with expansion, weakening repelling effect and so our Universe will eventually start collapsing to enclose the cycle ... ?
The simple models simply don't match observation. Strongly interacting particles tend to give pions, which decay into photons, which we simply don't observe. There are some people who think that dark matter could be microscopic, "relic" black holes which don't evaporate for some reason (don't ask me---I never understood why they don't decay via Hawking radiation). Apparently these models are not dead, but most physicists would call this idea "unlikely" or "just wrong", depending on who you talk to.
Equipartition of energy I'm not talking about particles, but about that EM isn't the only interaction we have and so background microwave radiation isn't the only kind of noise in space we should expect ... There are fields responsible for EM force and thermalization of their degrees of freedom is observed as CMB ... but we have also fields corresponding to other interactions and they have succeeding degrees of freedom for which thermodynamics says that small random interactions should lead to equipartition of their energies (1/2 kT, where T=2.725K for interacting degrees of freedom). en.wikipedia.org/wiki/Equipartition_of_energy Strong interaction is usually related with much larger energies than EM and the number of thermodynamical degrees of freedom grows with depth of potential well ...
