Have you ever wondered why you look up and see a dark sky at night? Help share science with the world: http://translate.minutephysics.com/ Subscribe to MinutePhysics! MinutePhysics is on Google+ - http://bit.ly/qzEwc6 And facebook - http://facebook.com/minutephysics And twitter - @minutephysics Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Music by Nathaniel Schroeder Thanks to Nima Doroud and Niayesh Afshordi for contributions and to Perimeter Institute for support. http://www.perimeterinstitute.ca/ Created by Henry Reich Created by Henry Reich