I don't disagree with jordanpg's reply, but it's even deeper than that. Physicists think about theories and talk about theories as if they were reality. It's a

I don't disagree with jordanpg's reply, but it's even deeper than that. Physicists think about theories and talk about theories as if they were reality. It's a huge convenience. Remember, we can only keep five or ten things in focus at once (the "magic number seven, plus or minus two). By adopting the trick of treating a theory as reality we gain a huge cognitive convenience. The problem comes when we talk to non-scientists about this, who want to maintain a far less contingent view of the world. Knowledge isn't like that, though. Knowledge is contingent and uncertain (faith is certain.) The situation is far more complex than you suggest, in fact. "Dark Matter" is a name for a range of diverse phenomena that don't necessarily have anything to do with each other. We keep this in mind when talking amongst ourselves, but have never been able to get it clear to journalists. Galactic dark matter is what we use to explain rotation curves of spiral galaxies. It may be baryonic. As we go to larger scales there are different kinds of dark matter required--we know the baryon density of the universe and it isn't enough to explain what we see. We don't know if there is just one kind of exotic particle or many, and don't get me started on the cosmological constant. We talk about all this stuff as if it was real--and keeping in our heads models that are far more complex than the rough sketch of the idea you've presented as "the current definition"--because there's no reason not to. <em>We</em> know that it may be wrong. <em>We</em> know how radically contingent it all is. It's only when it gets to the general public, who have a very distorted view of how contingent our understanding of the world is, that people get upset, because they take the scientific discourse for something that it is not. In any case, this is absolutely not about funding. It's about epistemology and psychology.