In relativity, 'backwards in time' effects are ones that affect things in their own past-ward lightcone [1]. Only affecting things outside that cone might viola

In relativity, 'backwards in time' effects are ones that affect things in their own past-ward lightcone [1]. Only affecting things outside that cone might violate the light speed limit, but it won't violate causality. https://en.wikipedia.org/wiki/Light_cone https://en.wikipedia.org/wiki/Light_cone