DARK NATTER: This article makes the interesting point that the theory of dark matter is a lesser-of-two-evils theory, as the greater-evil theory would involve changes to the laws of gravity, something nobody is ready to do. Here's a big quote to elaborate:

Perhaps scientists don’t entirely understand the way gravity works; perhaps Isaac Newton’s famous law of gravitation needs some revising. But that idea, says the University of Arizona’s Chris Impey, is not very popular.

"Definitely most astronomers are extremely unwilling to give up Newton’s law," he says. "So it’s essentially a choice of two evils: You either hypothesize that Newton’s law is wrong, and that our knowledge of the gravity theory is incomplete. Or, you hypothesize a fundamental microscopic particle that has never been detected in any physics lab, whose properties are only constrained by these astronomical observations. Which is a pretty uncomfortable position for physicists to be in."

The article even mentions the luminous ether in the same paragraph as dark matter, the ether being the proposed substance that electromagnetic waves were propagated by and which was discarded as unneccessary later. Huh.