# How to go from Quantum World to Classical World? [duplicate]

In the quantum world we don't have specific trajectories, the particle so to speak goes through all possible paths. In the classical and macroscopic world we have definite paths, and usually one specific trajectory is assigned to a body's motion.

How would you go from a trajectoryless world to trajectoried world?

I guess there should be such a theory, cause one world is the building block of the other.

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## marked as duplicate by Emilio Pisanty, Qmechanic♦, dmckee♦Nov 24 '12 at 2:41

The concept of trajectory is an approximation both in quantum and classical mechanics (check above ref.); we recover trajectories when the states are localized $\sigma \rightarrow \delta$.