As many of you know, the universe is expanding rapidly.

It is accelerating.

This was not true until 5 billion years ago. We attribute this to dark energy, which we still know nearly nothing about.

Dark energy is everywhere.

Dark energy has the same energy density throughout all of space. It is about 7 × 10^−30 g/cm^3. This is extremely low compared to even the space of our solar system, which is about 6 protons per cubic meter. Dark energy is about 68% of the energy of the universe. The thing is, as it causes space to expand it does not delude. This means it increases in energy and strength over time. This is really bad for us. That means it accelerates exponentially and requires energy. Where does this energy come from? The most obvious conclusion seems to be all other forms of energy. That is not the only way it can kill you either. When the acceleration of space expanding gets too much for atoms to keep up, it will rip apart all matter.

(Andrew Z. colvin)

The edge of the universe.

Space expands from every single point, that means the farther away something is the faster it "moves" away. (I use moves as I lack a word for space expanding between objects, it does not actually move.) This means that at some point an object moves away from us faster than light can travel that distance. We are forever stuck in a "small" part of the universe unable to (except for warp drive) be able to see what else exists (hurry up on that warp drive). As the expansion accelerates the far away things are lost to us. This means the edge of the universe is getting (relatively) closer.

Why do we think dark energy exists?

Well a few reasons. As we have measured the universe is expanding at a certain rate that is accelerating. We have measured a red-shift in almost every Galaxy outside of our local cluster. During the big bang there was a large inflation period where the field force that created it disappeared, what did it degrade into?
Well that's about all the evidence I know of. Dark energy is by no means confirmed and we are still looking for evidence for and against it. It is called dark energy because we know nearly nothing about it and it does not interact with the electromagnetic spectrum, and thus is nearly impossible for our instruments to detect at this point.



more reading:https://en.wikipedia.org/wiki/Dark_energy
https://en.wikipedia.org/wiki/Metric_expansion_of_space
image source:www.nasa.gov/images/content/718568main_potw1301a.jpg
upload.wikimedia.org/wikipedia/commons/0/0f/Earth%27s_Location_in_the_Universe_SMALLER_%28JPEG%29.jpg