Much of what physicists have seen in our universe suggests that a large proportion of our universe is unseen; we live in a dark cosmos. What we can see makes up only 5% of the universe. The other 95% is totally invisible to us; its presence is discernible only by the weak effects it has on visible matter around it. This invisible stuff comes in two varieties: dark matter and dark energy. One holds the universe together; 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 latest discoveries of experimental physics have brought us closer to understanding them. 71 minutes. 2008.