newfag, honestly im a bit high and just want this question answerd, has bugged me for years and I dont know anyone smart enough to answer it.

Say we had an empty space with 3 balls.

Ball A is moving at 75% the speed of light

Ball B and C are at rest. Suddenly Ball B, would start moving in the same direction as ball A at 50% the speed of light. Would the time dilation being felt on ball A change or does it take Ball C moving at x% of speed of light for it to finally change. If so, when people say moving at x% the speed of light, what are they using as the reference point. Is there a absolute 0 for kinetic speed?

And if the last question is a no, does it mean that our universe is expanding at a rate in which they will infenintly aproach the speed of light?

Another question, if Ball a and b where at rest, a suddenly went 60% speed of light in direction a, and ball b suddenly whent 60% speed of light in the opposite direction. Would that be 120% the speed of light or is that just impossible.