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# 2: Wave-Particle Duality

In classical mechanics, waves and particles are two completely distinct types of physical entity. Waves are continuous and spatially extended, whereas particles are discrete and have little or no spatial extent. However, in quantum mechanics, waves sometimes act as particles, and particles sometimes act as waves—this strange behavior is known as wave-particle duality. In this chapter, we shall examine how wave-particle duality shapes the general features of quantum mechanics.