Click on the Play/Pause button to watch/stop the video. Use the other controls to change the volume, speed, quality, and size of the video. When you’re done watching the video, click on the Mark Complete button below the video to indicate that you’ve completed this course element. All users can read the associated discussion; however, only registered users can add or reply to comments about the video. This lecture was recorded on May 31, 2015 at the World Science Festival in New York City.