Hi, I wonder, if we have two spaceship and they are moving tovard each other at the same 0,9c speed. what is the relative speed as seen in the other ship? if our referance is another motionless ship. i think, ship's 0,9c speed seen ~0,4c and we're seeing they're closing each other, 0,4c speed. (or, am i wrong?) but, we're sitting the travelling ship. so, what is the other ship's relative speed? (sorry for my bad english) Thanks.