Electricity quantum electrodynamic theory

Another example of zero-point energy arises in the detailed quantum theory of the electromagnetic field, known as quantum electrodynamics. The empty vacuum with no photons present is actually the zero-point level with n = 0. The non-zero energy of this state cannot be measured directly, but does have some observable consequences. The vacuum is really a state of fluctuating electric and magnetic fields that are significant at the atomic level. Without them, there would be no mechanism for the spontaneous emission of photons from excited states. There also have very small effects on the energy levels of atoms (see Section 4.4). 

According to Primas (1991, p. 163), "the philosophical literature on reductionism is teeming with scientific nonsense," and he quotes, among others, Kemeny and Oppenheim (1956), who said "a great part of classical chemistry has been reduced to atomic physics." Perhaps it was not philosophers who invented this story after all. Almost certainly, Oppenheim and other philosophers of science at the time were familiar with the influential statements of Dirac, Heisenberg, Reichenbach, and Jordan on this issue. " Notoriously, the physicist Dirac (1929, p. 721) said, the underlying laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that exact applications of these laws lead to equations which are too complicated to be soluble." Less famously, the philosopher of science Reichenbach (1978, p. 129) reiterated that "the problem of physics and chemistry appears finally to have been resolved today it is possible to say that chemistry is part of physics, just as much as thermodynamics or the theory of electricity." These views clearly stuck. For example, in a recent review of quantum electrodynamics (QED), to which Dirac made important contributions, the historian of science Schweber (1997, p. 177) says, "the laws of physics encompass in principle the phenomena and the laws of chemistry."... 

The nature of media effects relates to the fact that, since the microscopic displacement field is the net field to which molecules of the medium are exposed, it corresponds to a fundamental electric field dynamically dressed by interaction with the surroundings. The quantized radiation is in consequence described in terms of dressed photons or polaritons. A full and rigorous theory of dressed optical interactions using noncovariant molecular quantum electrodynamics is now available [25-27], and its application to energy transfer processes has been delineated in detail [10]. In the present context its deployment leads to a modification of the quantum operators for the auxiliary fields d and h, which fully account for the influence of the medium—the fundamental fields of course remain unchanged. Expressions for the local displacement electric and the auxiliary magnetic field operators [27], correct for all microscopic interactions, are then as follows... 

In the preceeding sections we have shown the current status of quantum electrodynamical and related calculations in heavy hydrogenlike systems with its unique strong electric and magnetic fields. From our present experimental knowledge there is no contradiction to the theory of quantum electrodynamics as we use it nowadays. However, an increasing experimental precision may still point to deviations in the theory since in Lamb shift calculations the predictions are still at least one order of magnitude more precise than the best experimental values. On the other hand we... 

The Dirac equation did not take all the physical effects into account. For example, the strong electric field of the nucleus polarizes a vacuum so much that electron-positron pairs emetge from the vacuum and screen the electron-nucleus interaction. The quantum electrodynamics (QED) developed by Feynman, Schwinger, and Tomonaga accounts for this and similar effects and brings theory and experiment to an agreement of unprecedented accuracy. 

All science is based on a number of postulates. Quanmm mechanics has also elaborated a system of postulates that have been formulated to be as simple as possible and yet to be consistent with experimental results. Postulates are not supposed to be proved-their justification is efficiency. Quantum mechanics, the foundations of which date from 1925 and 1926, still represents the basic theory of phenomena within atoms and molecules. This is the domain of chemistry, biochemistry, and atomic and nuclear physics. Further progress (quantum electrodynamics, quantum field theory, and elementary particle theory) permitted deeper insights into the structure of the atomic nucleus but did not produce any fundamental revision of our understanding of atoms and molecules. Matter as described by non-relativistic quantum mechanics represents a system of electrons and nuclei, treated as pointlike particles with a definite mass and electric... 

Dyson-type equations have been used extensively in quantum electrodynamics, quantum field theory, statistical mechanics, hydrodynamic instability and turbulent diffusion studies, and in investigations of electromagnetic wave propagation in a medium having a random refractive index (Tatarski, 1961). Also, this technique has recently been employed to study laser light scattering from a macromolecular solution in an electric field. 

The accurate quantum mechanical first-principles description of all interactions within a transition-metal cluster represented as a collection of electrons and atomic nuclei is a prerequisite for understanding and predicting such properties. The standard semi-classical theory of the quantum mechanics of electrons and atomic nuclei interacting via electromagnetic waves, i.e., described by Maxwell electrodynamics, turns out to be the theory sufficient to describe all such interactions (21). In semi-classical theory, the motion of the elementary particles of chemistry, i.e., of electrons and nuclei, is described quantum mechanically, while their electromagnetic interactions are described by classical electric and magnetic fields, E and B, often represented in terms of the non-redundant four components of the 4-potential, namely the scalar potential and the vector potential A. 

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