My title might not be precise but I didn't know how to decribe it better.
I've been reading about the special and general theories of relativity for a short while and I started wondering. First, every movement is only relative to some other object/observer, there is no absolute movement/speed, correct? Assuming so, if an object moves at almost the speed of light relative to me, do I also move at almost the speed of light relative to it? If so, am I affected by all the "weird" effects that follow moving at such speeds (increased mass, different time flow, whatnot...)?
From everyday observation I'd have to say not but in that case what defines "moving at almost the speed of light"? Does it have to be relative to something (and what)? If not, is there any absolute measure of speed?
I know I might be talking nonsense but I'm new to these concepts and I'm trying to understand.