Quantum Mechanics and the Nature of Physical Reality

A discussion of wave-particle duality can be found in all modern textbooks dealing with theories of chemical structure and bonding (I). Almost all of these contain some summary of the experimental evidence in favor of such duality, which comes from studies of the physics of electromagnetic radiation (ohotons vs. waves) and "elementarv" oarticles ,. . such as electrons, protons, neutrons, etc. Undergraduate chemists tend to accept that this kind of behavior, although a t first sight pretty weird, is a true reflection of the real nature of matter a t the atomic and molecular level. Acceptance of this duality leads us directly to the wave functions and operators of the Schrodinger form of quantum mechanics. Wave-particle duality is manifested in the physics of elementary particles through Heisenberg's famous "uncertainty" principle. In essence, the principle states that it is impossible for us to measure simultaneously pairs of "conjugate" properties of particles (such as their position and momentum) without inherent uncertainties in both orooerties that are ;elated by the magnitude of Planck's co&&t. The uncertaintv ~rincinle is embodied in the Schrodinzer equation in whicc &ant& particles (like electrons) are described in terms of wave functions. Unlike classical mechanics, the Schrddinger form of quantum mechanics deals not with the observable properties (position, momentum, energy, etc.) but with the operators reauired to obtain the observables from the wave function that describes the system under study. Performing an experiment (asking the "particle" what it is doing) becomes equivalent to operating on the wave function with the quantum mechanical measurement operator appropriate to the property we are trying to observe. However, most students of chemistry have great difficulty with the conceot of the wave function. What is it? Is i t "real"? What dind of physical interpretation should it be given? Students in need of straight answers to such questions are rarely provided with them. I hope to demonstrate in this article that straight answers to these questions are not available.