What is a Path in QM and QFT ??? In classical mechanics, we are allowed to talk about path of a particle. But in quantum mechanics, the concept of path of a particle cannot be defined. This is due to the uncertainty principle. But Feynman talked about path integral in quantum mechanics. This probabilty integral gives more accurate prediction than any other theory. Yet the meaning of path is still not clearly defined. Then quantum entanglement also does not allow path description because of its limit of luminal speed. What is the meaning of path in modern physics?