For centuries, man has wondered on phenomena and processes happening around him.  As time passed, he was successful in applying his intuition and common sense in comprehending the stars, galaxies and their behaviour, but they fail in the microscopic world of molecules, atoms and sub-atomic particles.

Quantum theory provides us with the rules and regulations of the miniature world.  These rules are phenomenally successful in accounting for the properties of atoms, molecules, and their constituents, and form the basis of understanding the fundamental properties of all matter.  In fact, one may say that the greatest success story of the 20th-century physics is to confirm that this theory works, without a single exception, in spite of critical examination by some of the best minds spanning decades of time.

Yet, the conceptual foundation of quantum theory is mysterious.  It led to intense debates among scientists, and confused many.  Niels Bohr, one of the most prominent scientists in this domain, once remarked, 'You have not studied quantum mechanics [1] well if you aren't confused by it.'  Albert Einstein, the greatest physicist of the 20th century, never approved of this theory.  Bizarre though it may seem, quantum physics has led physicists step by step to a deeper view of the reality, and has answered many fundamental questions.

In the following chapters we shall touch upon several fascinating areas of the quantum world.  Our attempt is to help the reader understand the fundamental concepts of quantum physics without the underlying mathematics.  We try not to be physicists, but only to have an understanding of what physicists know of our world.  That goal is within our grasp.

Welcome aboard, to the quantum world!

Footnotes

1.  Usually one sees the term quantum mechanics used rather than quantum physics. This is directly related to Isaac Newton's original ideas.  Newton conceived of the universe as a vast machine, and so in Newtonian physics one could speak of the 'mechanics' or machine-like workings of the universe.  'Quantum mechanics' is simply the same idea applied to the world of atoms and sub-atomic particles -- though the machine-like workings of the quantum world are very different from those of the Newtonian world.

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