Alvin Powell in the Harvard Gazette:
Current models hold that the stuff we know about — ourselves, our cars, our houses, the solar system, interstellar dust, etc. — makes up just about 5 percent of the universe. A big chunk of the rest, 27 percent, is something called dark matter, whose gravitational effects astrophysicists see as they peer into the skies, but whose nature remains a mystery. The remainder — roughly 68 percent — is dark energy, about which scientists understand even less. (Chris Stubbs, the Samuel C. Moncher Professor of Physics and of Astronomy, is one of the number who are on the case, albeit at the Large Synoptic Survey Telescope in Chile rather than the LHC.)
Other mysteries include how gravity is related to the other three main forces in the universe: electromagnetism and the strong and weak forces that operate in the atomic nucleus. Today they’re explained by separate theories. A theorized particle, the graviton, that might carry the gravitational force, has never been seen. There’s also the question of whether supersymmetry — thought to include a whole new family of particles — is real. And then there’s the possibility that the Higgs boson hasn’t been fully described.
More here.