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9/21/09 |
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2.
Quantization
6. Duality |
Unit 2
Particle-Wave
Duality
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In Unit 1 of this course we learned that space void of all matter and energy was non-observable and hence, non-physical. In this unit we will explore the nature and structure of matter and energy.
By the beginning of the twentieth century, classical physics had learned to classify the distribution of matter into various categories. For example, localized mass and energy were associated with particles, distributed mass was associated with substances, and distributed energy was associated with waves.
Most phenomena in nature fit clearly into one of these categories or another. But at the dawning of modern physics, certain experiments were performed that began to blur the distinction between these categories. For example, experiments probing the structure of substances showed that the concept of a continuous mass distribution was an illusion. And experiments analyzing the spectrum of gasses demonstrated that energy also appeared in non-continuous distributions. Therefore, at their most fundamental levels, both mass and energy appeared to be quantized into discrete units, eventually called fundamental particles, atoms, charges, photons, etc. It took many scientists many decades to develop a consistent theory of this quantized phenomenon, but some of the consequences of quantization became evident relatively quickly.
The quantization of electromagnetic radiation (light) was the first quantum phenomenon to be explained. And it illustrates how quantum theory becomes essential when classical mechanics is pushed too far into the realm of the small.
According to Maxwell’s electromagnetic field equations the intensity of light can be made arbitrarily small. But experiments performed near the turn of the twentieth century demonstrated that there was a smallest unit of light energy for a given frequency. This smallest unit of light is now called a photon. And experiments show that photons possesses many of the characteristics normally associated with particles. Since light clearly is a wave phenomenon, the quantization of light demonstrates that waves have particle-like properties.
The quantization of matter manifests itself in the form of atoms and their constituent particles. But the structure of the atom was not obvious to scientists at first. Various models of the atom were proposed, tested, and rejected before a satisfactory picture emerged. Eventually, the structure of the atom was explained in terms of electrons, protons, and neutrons. Today, we recognize that protons and neutrons also have a structure that can be explained in terms of quarks. But experimental evidence suggests that certain particles, like electrons and quarks, are truly fundamental. They have no structure and are not made of smaller, more fundamental components. In essence, they can be treated as if they were ideal particles.
But again, when the classical concept of a particle is pushed too far, the predictions of classical physics deviate from observations. In fact, when small physical particles are looked at closely enough they began to exhibit wave-like properties.
Needless to say, the discovery that waves have particle-like properties and particles have wave-like properties was (and still is) more than a little disconcerting. The nature of particles and waves seem so mutually exclusive that it would be impossible for a single phenomenon to exhibit both properties.
But eventually the concept of wave-particle duality emerged which harmonized the apparent contradictions. And today, modern physics recognizes that there is only one classification for matter and energy. All fundamental manifestations of mater and energy exhibit wave-particle duality characteristics. All particles are waves, and all waves are particles, and all substances are composed of a collection of these wave-particle building blocks.
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