[Cboldt]

Dark Matter gets that name because its interactions appear to be limited to gravity, and so far, no lab experiment has observed any of this "stuff." The supposed function of dark matter is to explain why galaxies appear to rotate as a unit. Our solar system, in contrast, has slower moving planets in the more distant orbits.

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.

[Zeneta]

Can they create this model without it ?

BTW, all my questions are rhetorical.

[Mariner]

"why the expansion of the universe appears to be accelerating"

Yep, we're just one big explosion that hasn't stopped yet. Still in the momentum phase, but can that ever stop in infinite space?

[Gideon7]

Dark energy is a total hack. Nothing in the Standard Model explains it. There's no reason for it. It's just there. There is no force carrier particle. It actually is an intrinsic part of space itself. And it's perfectly balanced.

There's a good layman's discussion of DE on the Science Channel (about 2.5 minutes). Physicists are baffled by it. It seems to even hide when they actively try to search for it.

With DE we avoid the depressing slow heat-death of the universe as the last star dies burns out with nothing left but a dead cinder.

Instead the universe will entire spectacularly (the Big Rip). And you can actually watch it happen 16+ billion years from now if you travel in an FTL spacecraft. You can actually sit in Douglas Adams' Restaurant at the End of the Universe and drink campaign as watch it all happen, faster and faster. The galaxies will fly apart, then the stars, then the planets, then you.

And then we have dark matter. Again the Standard Model doesn't explain it. There's no reason for it. It's just there. Why? Well, it certainly makes the galaxies pretty to look at. Otherwise they would be featureless fuzzballs. And you have to admit the Hubble images are indeed very pretty.

What's even more improbable is that we can actually see those galaxies. The matter density gradient function has to be balanced on a knife edge to see large structures at literally the opposite end of the universe (by all rights the sky ought to be a gray fog or all black). The Hubble Ultra Deep Field is the most improbable image ever taken.

Take all three together: the DE (Big Rip), DM (cool looking structures as cosmological distances), the UDF (we can actually see those structures). See a pattern?

It's all as if something, or someone, likes to show off His handiwork.

[Lx]

I thought dark matter was a fudge factor as when they calculated the big bang, too much matter was unaccounted for so they came up with dark matter.