The universe is astonishing in multiple ways, and one of its most probative features is the existence of its dark side: dark matter, interacting only via gravity, dark energy, the mysterious so-called energy of empty space that is accelerating the expansion of the universe, and black holes, from which not even light can escape. Free access to Closer to Truth's library of 5,000 videos: http://bit.ly/376lkKN Watch more interviews on dark matter and dark energy: https://bit.ly/3zXMuFM Joseph Silk is Homewood Professor of Physics and Astronomy at Johns Hopkins University. He studied at Cambridge, earned his PhD from Harvard in 1968, was a postdoctoral fellow at Cambridge and Princeton, and taught at the University of California, Berkeley, and the University of Oxford. Register for free at CTT.com for subscriber-only exclusives: http://bit.ly/2GXmFsP Closer to Truth, hosted by Robert Lawrence Kuhn and directed by Peter Getzels, presents the world’s greatest thinkers exploring humanity’s deepest questions. Discover fundamental issues of existence. Engage new and diverse ways of thinking. Appreciate intense debates. Share your own opinions. Seek your own answers.