Chapter 1


Man’s mind once stretched by a new idea, never regains its original dimension.

—Oliver Wendell Holmes


Physics deals with the study of behaviour of physical systems under various conditions. It boils down to the study of nature of interactions between particles—the constituents of physical systems—and the consequences thereof. At macroscopic level, almost all observed phenomena have been explained by invoking the laws of Newtonian mechanics, which is generally known as ‘classical mechanics’.

The very natural question which comes to our mind is ‘What is the need of any other mechanics (e.g. quantum mechanics) when very profound and well-tested mechanics (i.e. classical mechanics) is already there?’ For centuries, ...

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