The current theoretical model for the composition of the universe is that it's made of normal matter, dark energy and dark matter. A new University of Ottawa study challenges this.
Don't get too excited, this is a pretty fringe theory that doesn't really have experimental evidence. They were able to make some observations fit with their theory without dark matter yes, but not all of them. The tired light part in particular has a lot of contradictions with observation that they don't explain.
I'm a workshop kind of guy that enjoys space documentaries. For my part, I see "dark matter" as a known hole in our current understanding of cosmology, and I bet when we figure out how it does actually work it'll lead to some really cool TV shows.