1. Bonsor, Kevin, and Robert Lamb.  "How Time Travel Works"  20 October 2000. HowStuffWorks.com. <http://science.howstuffworks.com/science-vs-myth/everyday-myths/time-travel.htm>  10 April 2012.

2. "Doctor (Doctor Who)" 8 April 2012. Wikipedia. <http://en.wikipedia.org/wiki/The_Doctor_%28Doctor_Who%29> 10 April 2012.

3. Hafele, J.C. and Keating, Richard E. "Around-the-World Atomic Clocks: Predicted Relativistic Time Gains" 14 July 1972. Science 177(4044): 166-168.

4. "Hafele-Keating experiment" 5 April 2012. Wikipedia. <http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment> 10 April 2012.  

5. Kaku, Michio "Physics of the Impossible." New York. Doubleday, 2008.

6. "Time vortex (Doctor Who)" 10 April 2012. Wikipedia <http://en.wikipedia.org/wiki/Time_vortex_%28Doctor_Who%29> 10 April 2012.