Quotes from book
Principles of Quantum Mechanics

Name: Principles of Quantum Mechanics
Author: Paul Dirac

The Principles of Quantum Mechanics is an influential monograph on quantum mechanics written by Paul Dirac and first published by Oxford University Press in 1930.

“Classical mechanics has been developed continuously from the time of Newton and applied to an ever-widening range of dynamical systems, including the electromagnetic field in interaction with matter. The underlying ideas and the laws governing their application form a simple and elegant scheme, which one would be inclined to think could not be seriously modified without having all its attractive features spout. Nevertheless it has been found possible to set up a new scheme, called quantum mechanics, which is more suitable for the description of phenomena on the atomic scale and which is in some respects more elegant and satisfying than the classical scheme. This possibility is due to the changes which the new scheme involves being of a very profound character and not clashing with the features of the classical theory that make it so attractive, as a result of which all these features can be incorporated in the new scheme.”

Paul Dirac book Principles of Quantum Mechanics

I. The Principle of Superposition - 1. The Need for a Quantum Theory
The Principles of Quantum Mechanics (4th ed. 1958)

“Causality applies only to a system which is left undisturbed. If a system is small, we cannot observe it without producing a serious disturbance and hence we cannot expect to find any causal connexion between the results of our observations. Causality will still be assumed to apply to undisturbed systems and the equations which will be set up to describe an undisturbed system will be differential equations expressing a causal connexion between conditions at one time and conditions at a later time. These equations will be in close correspondence with the equations of classical mechanics, but they will be connected only indirectly with the results of observations.”

Paul Dirac book Principles of Quantum Mechanics

I. The Principle of Superposition - 1. The Need for a Quantum Theory
The Principles of Quantum Mechanics (4th ed. 1958)

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