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Nov 16
2009
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Wave-particle duality does not mean that a photon or subatomic particle is both a wave and particle simultaneously, but that it could manifest either a wave or a particle aspect depending on circumstances. Complementarity, uncertainty, and the statistical interpretation of Schrdinger's wave function were all related. Together they formed a logical interpretation of the physical meaning of quantum mechanics known as the "Copenhagen interpretation.
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Central to the Copenhagen Interpretation is the principle known as complementarity. That the wave and particle nature of objects can be regarded as complementary aspects of a single reality, like the two sides of a coin. An electron, for example, can behave sometimes as a wave and sometimes as a particle, but never both together, just as a tossed coin may fall either heads or tails up, but not both at once.
One must resist the temptation to regard matter or photon waves as waves of some material substance like sound or water waves. The correct interpretation, proposed by Born in the 1920's, is that the waves are measures of probability. Waves of probability relate to the uncertainty principle in that it cannot be certain what any given particle will do. Only betting odds can be given. This fundamental limitation represents a breakdown of determinism in nature. It means that identical electrons in identical experiments may do different things. But, statistically, the outcome of the experiment is predictable. Bohr, the leader of the Copenhagen Interpretation, admonished those who would ask what an electron really is, a wave or a particle. He denounced the question as meaningless or without context (such as `what is north of the north pole?'). To observe the properties of an electron is to conduct some sort of measurement. Experiments designed to measure waves will see the wave aspect of electrons. Those experiments designed to measure particle properties will see electrons as particles. No experiment can ever measure both aspects simultaneously and so we never see a mixture of wave and particle.
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The adoption of the Copenhagen Interpretation for quantum phenonmenon poses a sharp divide between classical or macroscopic physics and quantum or microscopic physics. In the macroscopic world events appear to be determinisitic. Every event has a cause. Often, the cause is difficult to directly determine, for example an apple falls from a tree because its stem weakens. We cannot tell exactly when it will fall, but we know some direct mechanical action is the cause and if we had percise knowledge of the state of its fibers we would know when and why. Thus, we resort to probabilities as a substitute for exact knowledge of the acting causes.
However, the conceptual abyss seems to separate classical from |
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