 An interpretation that avoids this conflict is to say that the rotating spheres experiment does not really define rotation "relative" to anything in particular (for example, absolute space or fixed stars); rather the experiment is an operational definition of what is meant by the motion called "absolute rotation".This sphere example was used by Newton himself to discuss the detection of rotation relative to absolute space.Checking the fictitious force needed to account for the tension in the string is one way for an observer to decide whether or not they are rotating – if the fictitious force is zero, they are not rotating.