Or at least try to identify the major external forces. The rest could be combined as noise. The question is, in this case, how would anyone know that all relevent forces have been identified and isolated, free from dependence. How would anyone know that there isn't a rogue force out there as yet still unidentified?
All the more reason to perform the experiment. Rigorously testing general relativity can make a physicist's career. Discovering a new force would make a physicist's name immortal. A Nobel Prize would be the least of it.