ABSTRACT
The motion of a particle in quantum mechanics is described by a complex wave function that gives the probability amplitude for finding the particle at point at time. Corresponding to every physical quantity is an operator. A particle whose state is an eigenstate of the operator has a definite value of the physical quantity. This value is just the eigenvalue belonging to the eigenstate. The relations between the spatial extents of the wave packet, that is, the uncertainty in the position of the particle, and the uncertainty in the momentum of the particle, are known as the Heisenberg uncertainty relations. They form the cornerstone on which the logical consistency of quantum mechanics rests.
