Quote Originally Posted by jwilliams View Post
What is the dark energy? I know this is not the easy question, but I really want to get the answer.
Well, it's easy in the sense that it's not too hard to say, "I don't know."

It's not just me, no one really knows what it is. So why are all these supposedly "smart" physics type people going on about it if they don't know what it is?

First of all, this is our normal state of being. Every answer leads to more questions (at least so far). It is common for people, even scientists, to lose sight of this when discussing the discoveries of the scientific process.

What we know that by our observations, the universe is not only expanding, but accelerating. Not only is it accelerating, which we would expect, due to all the gravitational acceleration sources about the place, but it's accelerating in the wrong direction... away from the attraction of gravity.

Expanding is easy enough to explain. There was a Big Bang... stuff is still 'sploding out from that bang. Did I mention it was Big? It was truly the Biggest of Bangs.

Now the universe is full of all this mass, and mass causes gravitational attraction. So we expect the rate of the expansion to be slowing down. However, we observe the rate of the expansion speeding up. That requires energy.

What is the source of this energy? We don't know. We have applied the name "dark energy" as a placeholder name in the mean time.

We don't know what it is, or even if it's a single thing or many things. We only know we observe a property of our universe which is beyond the ability of our current model to understand.