Dark Energy is due to light and is Electromagnetic in nature
With the following predicates,
1) galaxies getting brighter (according to Richard Bouwens at Santa Cruz)
2) the universe's expansion is accelerating
3) mostly likely (logically) the universe will collapse on itself, resulting in another big bang (neatly explains big bang origins)
I propose the following:
In order for the universe to collapse on itself and continue the cycle, the mysterious energy expanding the universe will have to weaken.
It seems that the weakening of Dark Energy will be around the time when galaxies are getting dimmer. This would result in the universe beginning to slow down, and start to collapse on itself.
The coinciding of these two events strongly suggests that light is the source of energy we call Dark Energy, and that it is electromagnetic in nature.
Perhaps light effects space between galaxies, away from gravitational fields, in some way as to cause the accelerated expansion.