Dark matter exists, so we got that going for us

Dark matter definitely exists:

New observations of a great big cosmic collision provide the best evidence yet that invisible and mysterious dark matter really does exist.

The collision, between two huge clusters of galaxies, is the "most energetic cosmic event, besides the Big Bang, that we know about," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

The impact split normal matter and dark matter apart, rendering the dark matter's gravitational presence observable.

Dark matter is sort of like the G-spot. We knew it was there. We knew it would probably be good if we found it. We just hadn't quite figured out how.

Anyway, a physicist I am not, so read this summary at Cosmic Variance for a thorough explaination of what the deal is and what the implications are for gravity physics:

That's huge news for physicists. Theorists now know what to think about (particle-physics models of dark matter) and experimentalists know what to look for (direct and indirect detection of dark matter particles, production of dark matter candidates at accelerators). The dark matter isn't just ordinary matter that's not shining; limits from primordial nucleosynthesis and the cosmic microwave background imply a strict upper bound on the amount of ordinary matter, and it's not nearly enough to account for all the matter we need. This new result doesn't tell us which particle the new dark matter is, but it confirms that there is such a particle. We're definitely making progress on the crucial project of understanding the inventory of the universe.