Neil Johnson shows how Global Positioning System devices use satellites and atomic clocks to work out your location. Subscribe for regular science videos: http://bit.ly/RiSubscRibe Watch the full first lecture of the series: http://www.rigb.org/christmas-lectures/watch/1999/arrows-of-time/back-to-the-future?utm_source=youtube&utm_medium=social&utm_term=description From the fabric of space-time to the limits of the quantum world, Neil Johnson takes us on a journey through time in his 1999 Christmas Lecture series "Arrows of Time". His first lecture looks at our understanding of the role of time in the Universe and asks: if the basic laws of physics are simple, why is the Universe so complex? Watch the full series: http://www.rigb.org/christmas-lectures/watch/1999/arrows-of-time 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