Cosmology is in a golden age with advances in technology enabling us to probe the physics of the very early universe. Princeton’s David Spergel explains that observations of the microwave background are snapshots of the Universe only three hundred thousand years after the Big Bang. These observations have answered many of the questions that have driven cosmology for the past few decades - but many remain unanswered. Find out what we know and what we hope to learn. Series: "Scientific Horizons" [Science] [Show ID: 17605]