Quantum Theory

Quantum Theory : 

In classical physics, particles were assumed to have well defined positions and momenta. These were considered as objective properties, whether or not their values were explicitly known to a physicist. If these values were not known, but were needed for further calculations, one would make reasonable (statistical) assumptions about them. For example, one would assume a uniform distribution for the phases of harmonic oscillators, or a Maxwell distribution for the velocities of the molecules of a gas. Classical statistical mechanics could explain many phenomena, but it was considered only as a pragmatic approximation to the true laws of physics. Conceptually, the position q and momentum p of each particle had well defined, objective, numerical values

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