We know dark matter exists, but now comes the hard part: figuring out what exactly it is
It makes up a quarter of the universe. Without it, galaxies would fall apart, and stars would spin off into space. Dark matter is five times more abundant than normal matter (the stuff that makes up trees and stars and us), yet scientists can’t see it or figure out what it is. The one thing they can say for sure: They’re getting closer to an answer.
WIMPs, or weakly interacting massive particles, got their name because they rarely run into normal matter. They’ve got to be big if they account for 27 percent of the universe. And they are suspected to be particles, but even that remains to be seen.
5: Even if scientists identify dark matter, they’ll be a long way from understanding how the universe works. The combined mass of dark and normal matter still leaves about 70 percent of the universe unaccounted for. What makes up the rest? Say hello to dark energy, a force so weird and mysterious that scientists will be puzzling over it long after the dark-matter case is closed.