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Suppose that the gravitational warping is cause by the presence of "structures" that exist in those other dimensions?

Well, that's rather an exotic idea, so in the absence of evidence it's hard to see why it should be preferred to what is, after all, a very prosaic explanation that fits the bill at least as well. Occam's razor, and all that.

But more to the point, what you've presented doesn't strike me so much as an alternative to dark matter, as it is a form of dark matter.

My reading of that comment was also that dark_lord was describing what I would consider a "form" or "explanation" of what "dark matter" is. I agree with your comment here.

As far as the "light changing speed" comments: I agree that the "evidence" is not very convincing as the experiments have typically emphasized an upper limit, and the precision of this is getting better. However, it is VERY easy to imagine an effect of light slowing but that a measurement of that decrease being hugely difficult because the mechanism responsible for the decrease is also changes the march of time, the "clock" (or "clocks") which was used for determining the speed for that experiment. Very different types of measurements would be needed for comparison to determine that, and I'm not certain such measurements are available.

Thanks for the pictures you added to the discussion, Physicist.

Yeah, late post, but I just found this thread.

Going with Occam's Razor, why postulate something as bizarre as "dark energy" as the reason for continued and accelerated expansion? It seems to me that the distance between galaxies has simply grown enough that gravity no longer has much, if any, effect, and the remaining impetus from the Big Bang is flinging them on. The initial deceleration was gravity *trying* to overcome the Big Bang-imparted velocity, but it wasn't enough, and now the great void beyond is sucking it all out. To use the popular "balloon" analogy, you have a balloon in a vacuum. For a while, the balloon wall's inherent cohesiveness slowed down the expansion, but now it's been overcome and the balloon has exploded. Occam's Razor. I see no need to postulate that something is continuing to "inflate" the balloon.

Background: Took Astronomy circa '96. Heard about dark matter; this is the first I've heard of dark energy. (To be honest, I really see no need to postulate exotic, undiscovered particles as the source for dark matter, either.)

BTW, why would experiments on gravity reactions at 0.1mm test models of dark energy when DE is supposed to operate over vast distances?
http://www.space.com/scienceastronomy/astronomy/cosmic_darknrg_020115-2.html