What is “Dark Matter/Energy” ?
Why is it called “Dark” ?
Can they create this model without it ?
Tis ‘dark’ because we cannot observei it.
Dark Energy gets that name for a similar reason, no observation of it. It is invoked to explain why the expansion of the universe appears to be accelerating.
They are phrases used to avoid the fact that the standard cosmological models don't conform to the actual data.
I've often wondered about that myself. You see magnets interacting with iron from afar. You see objects attracting each other in empty space. Supposedly it's caused by invisible waves. But what if it's waves riding particles of so-called dark matter? We can't see it. We can't detect it. We're just too dumb at this point. I just don't see how a wave of energy like gravity can act across completely empty space, without a medium, such as you find with sound waves using air as a medium. Scientists used to say atoms were the smallest indivisible particle. Then electrons, protons and later neutrons. Then they discovered those were divisible into quarks, and lots of different quarks there are. I think we're just too dumb to see really tiny particles that make up dark matter.