“A cosmic mystery of immense proportions, once seemingly on the verge of solution, has deepened and left astronomers and astrophysicists more baffled than ever. The crux… is that the vast majority of mass of the universe seems to be missing.” –William J. Broad
When we look out at the Universe, the other things we see — stars, galaxies, and as we’re learning, planets — look an awful lot like the ones right here in our own backyard. Sure, there are subtle differences, but at a macro scale, the Universe appears to look very much like the Universe near and dear to us.
So what a surprise it would be if it turned out that the Universe weren’t like us at all! In fact, when we ask the Universe what it’s made up of, it tells us that normal matter — protons, neutrons, electrons or anything made out of Standard Model particles — simply won’t cut it; that’s not the majority of what’s out there. Sounds crazy, right? Yet we have multiple, independent lines of evidence that all lead to the same conclusion: the mass of the Universe is mostly made out of dark matter!