Here's a good introduction to Special Relativity, which is what you asked about: http://www.av8n.com/physics/spacetime-welcome.htm http://www.av8n.com/physics/

Here's a good introduction to Special Relativity, which is what you asked about: http://www.av8n.com/physics/spacetime-welcome.htm http://www.av8n.com/physics/spacetime-welcome.htm