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- TL;DR Summary
- Given that motion in space is relative to the observer and that motion is limited to the speed of light, I am wondering how that relationship determines relative speed of objects that would seem to exceed the speed of light between them.

This is one of my thought experiments where I am drawing a big blank, If you have 2 objects approaching a 3rd object from opposite directions (just enough off to avoid collision) at 75% of the speed of light, the first assumption is that each observing the other would see the other object approaching at 150% of the speed of light. That can't be. What speed would each appear to be approaching as viewed by the other? I'm certain this must be less than 100% since true speed of anything is relative to the observer.

Just because an observer has accelerated to a speed that would pass the 3rd object at 0.75c does not mean their speed relation to any other object (doing the same at 180 degrees) can exceed 100% the speed of light. I would like to know what formulas apply to a case like this including at different speeds (0.8c and 0.9c) and different approach angles, (such as 120 degrees or 91 degrees).

Just because an observer has accelerated to a speed that would pass the 3rd object at 0.75c does not mean their speed relation to any other object (doing the same at 180 degrees) can exceed 100% the speed of light. I would like to know what formulas apply to a case like this including at different speeds (0.8c and 0.9c) and different approach angles, (such as 120 degrees or 91 degrees).