Printhttp://en.wikipedia.org/wiki/Minkowski_diagram
http://www.astro.ucla.edu/~wright/st_diags.htm
http://www.phy.syr.edu/courses/modules/LIGHTCONE/events.html
http://arxiv.org/ftp/physics/papers/0703/0703002.pdf
http://www.physics.byu.edu/faculty/allred/222%2011/minkowski%2011.pdf
http://www.trell.org/div/minkowski.html
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