Relativistic & Quantum Mechanics

A mathematical physical theory that grew out of Planck's quantum theory and deals with the mechanics of atomic and related systems in terms of quantities that can be measured, is called quantum mechanics. The subject developed in several mathematical forms all of which are, in fact, equivalent.

De Broglie’s theory that a particle can also behave like a wave was used by Schrödinger in his formation of wave mechanics, in which the wave like nature of matter leads directly to the idea that only certain energy levels are possible, corresponding to the existence of standing wave. Matrix mechanics was developed by Born and Heisenberg at about the same time that Schrödinger introduced wave mechanics. In matrix mechanics observable physical quantities such as momentum, energy and position are represented by matrices. Dirac in 1928 extended the principles of quantum mechanics so that they also satisfied the principles of relativity.

The fundamental difference between classical (or Newtonian) mechanics and quantum mechanics lies in what they describe. In classical mechanics, the future history of the particle is completely determined by its initial position and momentum together with the forces that acts upon it. Quantum mechanics also arrives at relationship between observable quantities, but the uncertainty principle suggests that the nature of an observable quantity is different in the atomic realm. The quantities whose relationships quantum mechanics explores are probabilities.

Quantum mechanics might seem a poor substitute for classical mechanics. However, classical mechanics turns out to be just an approximate version of quantum mechanics. In quantum mechanics only one set of physical principles is included both for micro world and macro world.

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Applets

Frame of reference

Rotating frame of reference

Space and time in special relativity

Space time lab

Time dilation

Twin paradox

Compton effect