Dark Matter and Dark Energy?
The new challenges of astrophysics and cosmology resulting from more distant observations of our universe have presented us with conditions that do not fit the known and accepted conclusions of earlier observations i.e., the most distant galaxies appear to be expanding faster than the closer galaxies (not consistent with the Hubble Constant).
Also, observations of large galaxies have shown that the orbit of outer stars are in step with the orbit of the inner stars but out of step with gravitational physics, that is to say, outer stars are being held in orbit by forces greater that gravity.
These observations have brought about the postulation, and then acceptance, of the existence of dark matter and dark energy to answer these and other anomalies.
I would like to suggest and alternative theory for both conditions that does not require dark matter and dark energy to be a factor.

First- Is time slowing (other than as described by Einstein)? It is reasonable that time began with the Big Bang. Inflation modeling suggests that the beginning of the new universe was expanding faster than the speed of light “c”. If one considers time moving faster then, perhaps, the inflation rate was in line with “c”.
The graph suggests that time could have changed as a factor of the energy, matter and gravity density and is not linear. A more accurate time curve interpolation might be created by reviewing the Hubble red shift and connecting it to our latest distant observations of red shift. (One might infer that time would speed up if and when the universe expansion reversed, ultimately returning to zero time)
Second- Does gravity attract gravity? One might ask, when did gravity first reveal itself? Was it a constituent of the “soup” that evolved after the big bang or was it a part of the big bang energy? Does energy convert to gravity only when energy transforms to matter?
We know gravity attracts mass hence it attracts its gravity as well.
Gravity does not cancel gravity. Gravity does not repel gravity. (There is no proven antigravity).
As the stars burn, they loose mass. So, it follows that they loose gravity. Where does the lost gravity go… with the energy? If so, energy must have gravity.
Gravity attracts energy. (Einstein) Hence, gravity must attract gravity.
Free gravity? Gravitational waves? Can gravity be separate from energy? Does gravity have an indivisible quantity? Assume that light from the stars continues into space carrying with it a component amount of gravity. When the light diffuses (to spaced photons and gravitons), is there a point that it can not hold the gravitational component and free gravity is released? If there were free gravity and gravity attracts gravity it could “condense” to create clouds or “spokes” of gravity that could influence the behavior of galactic matter as well as intergalactic matter.