The Restless universe
|Introduction to The restless Universe|
1 The lawful Universe2 The clockwork Universe
5 The uncertain Universe» An introuduction to The uncertain Universe 1/2
Other titles in the Physical World series
5 The uncertain Universe
An introduction to the uncertain UniversePart 1 of 1 | Part 2For a printable version of 'The uncertain Universe' click here
Despite the impact of relativity, the greatest source of change in the scientific world-view in the twentieth century has undoubtedly been the development of quantum physics. This is the branch of physics that is mainly concerned with microscopic entities such as atoms and molecules, and their constituents.
So great has been its effect that it is now conventional to divide physics into two parts; quantum physics and classical physics, where, by classical physics, we mean anything that is not quantum physics. To be fair, it should be noted that some authors prefer to define classical physics as consisting of those subjects that were already well-defined by the year 1900, together with their direct developments in the twentieth century. In this way they include mechanics, thermodynamics and electromagnetism, but they exclude special and general relativity. Most physicists, however, would not hesitate to say that general relativity was a classical theory of gravity, and would regard relativity as the culmination of classical physics rather than a step beyond it. In any event, there can be no doubt that the development of quantum physics has demanded a fundamental change in outlook by physicists.
Quantum physics was born in 1900, but it took about twenty five years to reach maturity. During the first quarter of the twentieth century it had a rather rickety feel; there was not really any coherent theory of quantum physics, just assorted quantum ideas that were so successful in solving certain outstanding puzzles that it seemed there had to be something behind it all. The strongest characteristic of quantum physics during this early period was an emphasis on graininess or discreteness.
Indeed, the word quantum actually comes from the Latin for 'unit of quantity' or 'amount' and was introduced into physics by the German scientist Max Planck (1858-1947), in the course of his investigations into the emission of electromagnetic radiation from hot surfaces.
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