# 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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This has been addressed in e.g. Classical Limit of the Feynman Path Integral. –  Emilio Pisanty Nov 23 '12 at 15:30
Other Possible duplicates: physics.stackexchange.com/q/32112/2451 and physics.stackexchange.com/q/17651/2451 –  Qmechanic Nov 23 '12 at 15:35
The concept of trajectory is an approximation both in quantum and classical mechanics (check above ref.); we recover trajectories when the states are localized $\sigma \rightarrow \delta$.