The sky is getting darker and darker. There is going to be a thunderstorm.

The leading idea for dark energy is that it is a cosmological constant.

What's wrong with my bathroom floor? Nothing. It's just old and dingy, that's all.

We say that it has a gravitational pressure, which ordinary matter and dark matter do not.

So, as the universe expands as it is doing right now, there will be more and more dark energy.

With the Bifrost gone, how much dark energy did the Allfather have to muster to conjure you here, your precious Earth?

This dark energy doesn't behave like any other substance we know at all and acts more like anti-gravity force.

I'm thinking about how one could use the fact that a rapidly rotating mirror turns virtual photons into real ones as a method of observing dark energy.

That means it has the strange property that it expands as the volume of space increases to keep its energy density constant.

Because of this property of the cosmological constant, the future universe will be more and more dominated by dark energy, becoming colder and colder and expanding faster and faster.