THE STORY OF QUANTUM MECHANICS
By Victor Guillemin
Reviewed by John Ed Robertson
Two of the central tenets of quantum mechanics are Heisenberg’s Uncertainty Principle and the Schrodinger wave equations. The Uncertainty Principle states that the precise position and momentum of a particle cannot be known simultaneously. The amount of the uncertainty is related to Planck’s constant which is so small that it only becomes significant for sub-atomic particles, such as electrons. Another implication of this principle is that a particle can only have certain discrete energy levels related to Planck’s constant, which is also used to calculate uncertainty. Bohr’s model of the atom that we learned in high school chemistry was an attempt to explain these discrete energy levels in the form of electron shells. The fact that particles can only have discrete energy levels is the reason the term quantum mechanics is used. Guillemin writes:
"The uncertainty principle has sometimes been misconstrued to imply that a particle has both a precise position and momentum until it is disturbed by the experimenter, that the act of observing the position ‘destroys’ the precise momentum, in other words that nature is involved in a bizarre conspiracy to prevent the discovery of something that has real existence. Contrary as it may seem to all familiar experience; it is nearer to the truth to assert that a particle has neither a position nor momentum and that the act of observation creates its mechanical state."
I find that his choice of the word "creates" is unfortunate. I think that "assigns" would be a more appropriate word. The observer cannot create anything, but he can assign values based on his best guess. It is easy to see how statements like this contributed to the postmodern idea that reality is created rather than discovered.
This helps explain how quantum mechanics has helped to free us so that "The old classical determinism need not oppress us any longer." Further quoting Guillemin:
"Thus, the impossibility of predicting future events precisely is not due to an inadequacy in the method of prediction, but to the impossibility of obtaining the precise knowledge of the initial conditions upon which the prediction must be based."
"However, if Planck’s constant were zero (i.e. if there were no uncertainty) there would have been no Planck, and indeed no rational beings, or any forms of life, for it is quantization that accounts for the existence of stability and organization in the atomic substratum of the universe. Without quantization, there could be no definite normal state. Any electronic configuration whatsoever would be possible, and the slightest disturbance could alter this configuration permanently. Atoms would have no stable and specific properties. The universe would be a formless and meaningless blob without history, purpose or plan. In our present earthly environment, quantization alone makes atoms act - to use Newton’s words - ‘like the solid massy, hard, impenetrable particles formed by God in the beginning that nature may be lasting’."
The "always" and "never" of classical laws have been replaced by "usually" and "seldom". The development of quantum mechanics has been a sobering experience. It has shown where the limits of intuitive comprehension lie.
Guillemin, Victor; The Story of Quantum Mechanics; Charles Scribner’s Sons; 1968