I really can't understand how faster than light travel creates the cause and effect paradox. I have spent many days on internet searching this specific problem but not able to get it. Can some one explain it to me in the easiest way. Another question : i have read many times that if some one move away from earth at some speed lets say 0.99c, then after we come back to earth the clocks on earth shows more time elapsed than the clock which are at motion at 0.99c, ok i perfectly understand that because as we starts moving our time slows down to keep the light speed constant relative to us. but there is a thread on this forum where all the posters are saying that when we are in motion (lets say at 0.99c ) with relative to earth, we experience our selves to be perfectly normal but we will observe that time on earth has slowed down. Now these two statement which i have written in bold are contradicting each other. cause when in motion it is said that we will observe the time on earth has slowed down, but on the other hand they also say when we come back to earth clock there are showing more time and earth has move into the future. ???? how is that possible. do we observe sudden change in earth time when we come to rest ??? thanks.