Dark Cosmos: In Search of Our Universe's Missing Mass and Energy

Everyone knows that there are things no one can see, for example, the air you're breathing or a black hole, to be more exotic. But not everyone knows that what we can see makes up only 5 percent of the Universe. The rest is totally invisible to us.

The invisible stuff comes in two varieties—dark matter and dark energy. One holds the Universe together while the other tears it apart. What these forces really are has been a mystery for as long as anyone has suspected they were there, but the l...