Quantum Mechanics Explained

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This is based on the book by renowned physicist and author Brian Greene, taking us to the frontiers of physics to see how scientists are piecing together the most complete picture yet of space, time, and the universe. With each step, audiences will discover that just beneath the surface of our everyday experience lies a world we'd hardly recognize—a startling world far stranger and more wondrous than anyone expected.
Brian Greene is going to let you in on a secret: We've all been deceived. Our perceptions of time and space have led us astray. Much of what we thought we knew about our universe—that the past has already happened and the future is yet to be, that space is just an empty void, that our universe is the only universe that exists—just might be wrong.
Interweaving provocative theories, experiments, and stories with crystal-clear explanations and imaginative metaphors like those that defined the groundbreaking and highly acclaimed series "The Elegant Universe," "The Fabric of the Cosmos" aims to be the most compelling, visual, and comprehensive picture of modern physics ever seen.
Quantum mechanics (QM - also known as quantum physics, or quantum theory) is a branch of physics dealing with physical phenomena where the action is on the order of the Planck constant. Quantum mechanics departs from classical mechanics primarily at the [[|atomic spacing|atomic]] and subatomic scales, the so-called "quantum realm". QM provides a mathematical description of much of the dual particle-like and wave-like ("wavicle") behavior and interactions of energy and matter.
In advanced topics of quantum mechanics, some of these behaviors are macroscopic and only emerge at extreme (i.e. very low or very high) energies or temperatures. The name "quantum mechanics" derives from the observation that some physical quantities can change only in discrete amounts (Latin quanta), and not in a "continuous" (cf. analog) way. For example, the angular momentum of an electron bound to an atom or molecule is quantized. In the context of quantum mechanics, the wave--particle duality of energy and matter and the uncertainty principle provide a unified view of the behavior of photons, electrons, and other atomic-scale objects.
The mathematical formulations of quantum mechanics are abstract. A mathematical function called the wavefunction provides information about the probability amplitude of position, momentum, and other physical properties of a particle. Mathematical manipulations of the wavefunction usually involve the bra-ket notation, which requires an understanding of complex numbers and linear functionals. The wavefunction treats the object as a quantum harmonic oscillator, and the mathematics is akin to that describing acoustic resonance. Many of the results of quantum mechanics are not easily visualized in terms of classical mechanics - for instance, the ground state in a quantum mechanical model is a non-zero energy state that is the lowest permitted energy state of a system, as opposed a more "traditional" system that is thought of as simply being at rest, with zero kinetic energy. Instead of a traditional static, unchanging zero state, quantum mechanics allows for far more dynamic, chaotic possibilities, according to John Wheeler.
The earliest versions of quantum mechanics were formulated in the first decade of the 20th century. At around the same time, the atomic theory and the corpuscular theory of light (as updated by Einstein) first came to be widely accepted as scientific fact; these latter theories can be viewed as quantum theories of matter and electromagnetic radiation, respectively. Early quantum theory was significantly reformulated in the mid-1920s by Werner Heisenberg, Max Born, Wolfgang Pauli and their collaborators, and the Copenhagen interpretation of Niels Bohr became widely accepted. By 1930, quantum mechanics had been further unified and formalized by the work of Paul Dirac and John von Neumann, with a greater emphasis placed on measurement in quantum mechanics, the statistical nature of our knowledge of reality, and philosophical speculation about the role of the observer. Quantum mechanics has since branched out into almost every aspect of 20th century physics and other disciplines, such as quantum chemistry, quantum electronics, quantum optics, and quantum information science. Much 19th century physics has been re-evaluated as the "classical limit" of quantum mechanics, and its more advanced developments in terms of quantum field theory, string theory, and speculative quantum gravity theories.

Added on Nov 27, 2012 by lonewolf

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