wave-Particle duality(part-1)
The behavior of a microscopic "particle" differs in subtle ways from that of a classical particle; in some respects, it resembles the behavior of a classical wave. So before we plunge into the microworld, let's remind ourselves of the classical pictures of particles and waves.
In Particles and Their Trajectories in Classical Physics we reviewed the characteristics of a classical particle and the analysis of its motion using Newtonian mechanics. For example, a macroscopic particle has a well-defined position and linear momentum at any time, and from these observables we can calculate its energy. Essential to this description is the notion of spatial localization . The idea that a particle is a localized thing is implicit, for example, in the description of transport of energy through space by a particle in a localized lump. This quality of the classical description of a particle is, in turn, reflected in the "state descriptor" of Newtonian theory: the trajectory.
The characteristics of a wave are quite different from those of a particle. A wave is not spatially localized-this quality is reflected in the properties by which we characterize a wave, such as the wavelength . Like a particle, a wave carries energy and momentum, but it does so in a non-localized manner, distributed over a wave front. And a wave exhibits distinctive, non-particle-like behavior such as diffraction, interference, and polarization. Not surprisingly, then, the theory classical physicists use to describe the propagation of a wave and its interaction with matter-the electromagnetic theory of James Clerk Maxwell (l831-1879)-is quite different from that of Newtonian particle dynamics. So at the macroscopic level, classical physics elegantly and cleanly separates into wave mechanics and particle dynamics.
Alas, this division does not apply to microscopic particles, which adamantly refuse to adhere to either the classical wave model or the classical particle model. In some circumstances microscopic particles behave according to the laws of classical mechanics.
For example, some collisions of highly energetic atoms with molecules can be explained by using classical collision theory . Yet, in other circumstances quantum particles behave like waves: e.g., electrons that have been scattered by a crystal exhibit a diffraction pattern when they are detected. Analysis of this pattern reveals that in this experiment the electrons propagate precisely as though they had a well-defined wavelength and frequency . .. as though they are waves.!
"This situation," you may be thinking, "is a mess. You tell me that light isn't a wave. And electrons aren't particles. Well, then, what are they? And how can I understand the behavior of electrons if not with Newtonian mechanics, and of waves if not with Maxwell's theory? What is going on here?"
Michael A. Morrison - Understanding Quantum Physics.
By. Fady Tarek
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