We have a theory of the big bang,which could not be disproven yet.
This theory would expect that our current universe would slow down in expansion.
However our observations show that expansion is accelerating.
Introduce dark energy. It is supposed the mystical force which expands the universe.
(not sure if I get the following right)
This force acts on every atom. But it is weak on its own, even the weak gravitational force is stronger. However over great distance the force is bigger than the gravitation.
Then there is dark mater. Our visible universe was made into a simulation where they use all the physics we know of to simulate the currently visible situation. However the simulation did not behave like what we see. It only works when they added a lot of matter. But matter that you can't see? "dark matter"
Then they formed new theories that both dark matter and energy needed to exist or our universe wouldn't look like it looks today.
Now I am no scientists but it is possible that we are completely wrong here.
Dark matter isn't based on simulations, it's entirely observational.
We observe here that matter generates a gravitational force proportional to the amount of matter present, and we know that to an extreme degree of precision, but when we look at big things like galaxies the force required to shape and move them in the ways we observe would require more matter than we observe within them.
To expand on this, we also have mapped it out and know that the amount of dark matter varies wildly between galaxies, with some having basically none while others have far more dark matter than observable matter in them. There’s also a lot of stuff with the early universe that only works if you have something with gravity that doesn’t otherwise interact significantly with matter.
As Angela Collier puts it, dark matter is not a theory, it is a set of observations.
"dark" in scientific terms just means unexplained. We're very, very, very, and I cannot stress this enough... VERY sure that dark matter and dark energy exist, but they will remain "dark" until we discover what they are/what's causing the effects that we see. Aether was just unfounded non-sense that was based on practically nothing.
I'll agree on Dark Matter, things like the Bullet Cluster need something more than modifyed gravity, but I'm not so sure about Dark Energy. As far as I know, Dark Energy is the difference in the energy we measure in space and the energy necessary to fuel the acceleration of expansion. This whole idea could change radically with a new understanding of space or the nature of the universe.
Dark Matter is a relatively known unknown; we know there must be some thing here, and are nearly certain it's more than just a force. Dark Energy is an unknown unknown; something doesn't match up, but we don't know what.
Ummm... Only thing we're sure of is that those gravitational effects exist. Dark matter and dark energy are theorized to explain the real gravitational effects that we don't understand. We don't "know of their existence," there are other theories to explain the gravitational effects.
At this point there's more evidence for psychic powers than Dark Matter, that is not praise for Parapsychology but rather condemnation of "Bro, it's real! Source: Trust me!" being Dark Matter's only evidence.