翻訳と辞書 Words near each other ・ Wheels on the Bus ・ Wheels Stop ・ Wheels Up Tour ・ Wheelerigobius ・ Wheelers (novel) ・ Wheelers Bay ・ Wheelers Hill Secondary College ・ Wheelers Hill, Victoria ・ Wheelers Primitive Baptist Church ・ Wheelersburg High School ・ Wheelersburg, Kentucky ・ Wheelersburg, Ohio ・ Wheelerville, Missouri ・ Wheelerwood, Iowa ・ Wheeler–DeWitt equation ・ Wheeler–Feynman absorber theory ・ Wheeler–Lea Act ・ Wheeler–Stallard House ・ Wheeler–Watkins Baseball Complex ・ Wheeless, Oklahoma ・ Wheelgate Park ・ WheelGroup ・ Wheelharp ・ Wheelhouse ・ Wheelhouse (album) ・ Wheelhouse (archaeology) ・ Wheelhouse (surname) ・ Wheelhouse Magazine ・ Wheelhouse Maritime Museum ・ Wheelie Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Wheeler–Feynman absorber theory ： ウィキペディア英語版 Wheeler–Feynman absorber theory The Wheeler–Feynman absorber theory (also called the Wheeler–Feynman time-symmetric theory), named after its originators, the physicists Richard Feynman and John Archibald Wheeler, is an interpretation of electrodynamics derived from the assumption that the solutions of the electromagnetic field equations must be invariant under time-reversal transformation, as are the field equations themselves. Indeed, there is no apparent reason for the time-reversal symmetry breaking which singles out a preferential time direction and thus makes a distinction between past and future. A time-reversal invariant theory is more logical and elegant. Another key principle, resulting from this interpretation and reminiscent of Mach's principle due to Tetrode, is that elementary particles are not self-interacting. This immediately removes the problem of self-energies. ==T-symmetry and causality== The requirement of time reversal symmetry, in general, is difficult to conjugate with the principle of causality. Maxwell's equations and the equations for electromagnetic waves have, in general, two possible solutions: a delayed solution and an advanced one. Accordingly, any charged particle generates waves, say at time $t\_0=0$ and point $x\_0=0$, which will arrive at point $x\_1$ at the instant $t\_1=x\_1/c$ (here $c$ is the speed of light) after the emission (retarded solution), and other waves which will arrive at the same place at the instant $t\_2=x\_1/c$ before the emission (advanced solution). The latter, however, violates the causality principle: advanced waves could be detected before their emission. Thus the advanced solutions are usually discarded in the interpretation of electromagnetic waves. In the absorber theory, instead charged particles are considered as both emitters and absorbers, and the emission process is connected with the absorption process as follows: Both the retarded waves from emitter to absorber and the advanced waves from absorber to emitter are considered. The sum of the two, however, results in ''causal waves'', although the anti-causal (advanced) solutions are not discarded ''a priori''. Feynman and Wheeler obtained this result in a very simple and elegant way. They considered all the charged particles (emitters) present in our universe, and assumed all of them to generate time-reversal symmetric waves. The resulting field is :$E\_\backslash mathrm(\backslash mathbf,t)=$ \sum_\frac,t)+E_n^\mathrm(\mathbf,t)}.\ Then they observed that, if the relation :$E\_\backslash mathrm(\backslash mathbf,t)=\backslash sum\_$ \frac,t)-E_n^\mathrm(\mathbf,t)}=0 holds, $E\_\backslash mathrm$, being a solution of the homogeneous Maxwell equation, can be used to obtain the total field :$E\_\backslash mathrm(\backslash mathbf,t)=$ \sum_\frac,t)+E_n^\mathrm(\mathbf,t)}+ \sum_\frac,t)-E_n^\mathrm(\mathbf,t)} =\sum_E_n^\mathrm(\mathbf,t). The total field is retarded and causality is not violated. The assumption that the ''free field'' is identically zero is the core of the absorber idea. It means that the radiation emitted by each particle is completely absorbed by all other particles present in the universe. To better understand this point, it may be useful to consider how the absorption mechanism works in common materials. At the microscopic scale, it results from the sum of the incoming electromagnetic wave and the waves generated from the electrons of the material, which react to the external perturbation. If the incoming wave is absorbed, the result is a zero outcoming field. In the absorber theory the same concept is used, however in presence of both retarded and advanced waves. The resulting wave appears to have a preferred time direction, because it respects causality. However, this is only an illusion. Indeed it is always possible to reverse the time direction by simply exchanging the labels ''emitter'' and ''absorber''. Thus, the apparently preferred time direction results from the arbitrary labelling. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wheeler–Feynman absorber theory」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.