We're in the dark
Recent measurements of the cosmic microwave background (radiation leftover from the universe's early hot and dense state) support the hypothesis that dark matter and dark energy make up 95% of everything in existence.
But what's the matter?
Isn't it fascinating and mind-boggling that we have almost no idea what the majority of the stuff in our universe is? There are dark matter and dark energy are not rather than explain what these mysterious stuffs are. E.g., dark matter is not just dark clouds of normal matter (called baryonic matter); it is not antimatter; it is not huge black holes. But it is 25% of the universe.
Current research on dark energy hasn't faired better: Is it a property of space, as suggested by Einstein's cosmological constant? Perhaps it's a result of the quantum mechanics of space; maybe it's a new kind of energy field. It's also possible that Einstein was wrong. It wouldn't be the first time a seemingly brilliant solution, explaining everything known at the time, was later replaced. Think "ether." Think "animal spirits." Think "caloric fluid." That said, there's nothing better to replace it yet. At least this time we're acknowledging the fact that the names "dark energy" and "dark matter" refer to stuff we don't yet understand.
The quest goes on
The Joint Dark Energy Mission, a space probe designed to study dark energy, has been in the works for a while now. The mission is currently in a tight spot as NASA, the Department of Energy, and the European Space Agency tussle over who's in charge of which parts of the probe and who's paying for what. Don't you love international politics? A lot of people, such as the folks at the Cosmic Variance blog are up in arms about the disagreements--can't we all just get along and do science?