Wave-Particle Duality

Atomic models began to resemble the still-popular image of electrons orbiting a nucleus at the beginning of this century. The electron was, of course, considered a real physical chunk. The first sign of trouble came in 1905 with Albert Einstein's work on the photoelectric effect. At that time it was easy to demonstrate and widely accepted that light traveled in waves, but the production of electricity from light striking metal led Einstein to hypothesize that a light wave also has the nature of a particle, now called the photon. The success of this theory inspired Louis de Broglie to turn the tables and describe the electron as a wave, which helped explain many features of the atomic model of that time. To make a long history of research and theorizing short, physicists developed a way to describe the behavior of sub-atomic phenomena in terms of both waves and particles by means of mathematics, specifically through the use of Max Planck's constant. (19)

The mechanical worldview from which these theories of waves and particles sprang had a pronounced streak of determinism. It had long been felt that it was possible, in theory, to know the future of the universe, if only all the collisions of particles could be charted at once. The human observer was merely a passive chronicler of events that were occurring absolutely, that is, independent of the observer's frame of reference or method of investigation. The dual wave-particle nature of electrons flew in the face of such beliefs. While Erwin Schrodinger came up with a mathematical equation that nicely described de Broglie's waves, others saw definite evidence of particulate behavior, which made the cloudlike wave pattern of the electron ontologically distasteful.

The picture became clearer after Max Born hypothesized that the cloud was in fact a probability wave. If one finds an electron, plots its position, then repeats the process many times, eventually a pattern shows up. However, the wave pattern does not say where the particle is at any given moment, merely where it is likely to be. The rule established is that the square of the wave amplitude at any point in space gives the probability of finding the electron at that point. (20) Conversely, knowing where the particle is does not tell us anything about its wave function. It turns out that there is no way to simultaneously know both the position and path of the particle, not because of inadequate technology but because of the very act of observation.

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Copyright © 2005 Dan Haig