Dark Energy

72% of the universe is dark energy, 4.6% is atoms, and ~23% is dark matter.

Dark energy is a force that is trying to push the universe apart.  Dark matter is trying to clump things together.   And it is the interplay of these two things that has led to the formation of the structures we see in the universe today.  And so by understanding how fast the galaxy clusters form and clump together, that tells us about dark matter, but also about how much dark energy is pushing it apart at the same time. 

 

Similar to dots on a balloon - when you blow up the balloon - they all move farther away from each other.

Eventually, dark energy will expand the universe so much that it will be nothing but cold and empty space. 

Beyond the Shadow of a Doubt?

Dark Energy Independently Confirmed

The gravitationally repulsive presence, thought to make up most of the universe, shows its effect on the development of galaxy clusters

Dark Energy Is Real, New Evidence Indicates

SPACE.com

A census of 200,000 galaxies may confirm that the mysterious force of dark energy is what is pulling the universe apart at ever-increasing speeds, a new study finds.

The results of the five-year galactic survey offer new support for the favored theory of how elusive dark energy works – as a constant force, uniformly affecting the universe and driving its runaway expansion.

The new findings contradict an alternate theory that gravity, and not dark energy, is the force pushing space apart and causing it to expand. That alternate theory challenges Albert Einstein's concept of gravity, because it has gravity acting at great distances as a repulsive force rather than an attractive one. [6 Weird Facts About Gravity]

The galaxy survey, which looked at galaxies that were up to 7 billion years old, used data from NASA's space-based Galaxy Evolution Explorer (GALEX) and the Anglo-Australian Telescope on Siding Spring Mountain in Australia.