Frank Close looks at how observations from galaxy rotation and gravitational lensing can imply the existence of dark matter. Watch the full lecture: http://www.rigb.org/christmas-lectures/watch/1993/the-cosmic-onion/an-hour-to-make-the-universe?utm_source=youtube&utm_medium=social&utm_term=description Frank Close gave the 1993 lectures "The Cosmic Onion" tracing a hundred years of discovery and invention In his final lecture, Frank Close looks at the parts of the universe that are invisible to us. Watch the full series: http://www.rigb.org/christmas-lectures/watch/1993/the-cosmic-onion?utm_source=youtube&utm_medium=social&utm_term=description The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and Tumblr: http://ri-science.tumblr.com/ Our editorial policy: http://www.rigb.org/home/editorial-policy Subscribe for the latest science videos: http://bit.ly/RiNewsletter