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The Lorentz-Dirac equation and positive-definite energy in classical electrodynamics

Уравнение Лорентца-Дирака и положительно определенная энергия в классической электродинамике

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Il Nuovo Cimento B (1971-1996)

Summary

We show that, in a previously developed theory of classical electrodynamics, whereeach charged classical electron has itsown electromagnetic field (and the mutual interactions between a given charge and the field of another charge make up the elementary interactions of the theory), the requirement of positive-definite total energy automatically yields the generalized form of the Lorentz-Dirac equation of motion for the charges. This occurs without the presence of direct self-interactions, hence the theory is finite and consistent without the need of infinite-renormalization techniques. The proof that this new classical electrodynamic formalism produces the same class of equations of motion, as that of renormalized Maxwell-Lorentz theory (without infinities from an internal positive-definite energy criteria), suggests that an attempt to quantize the new formalism might lead to a better formulation of quantum electrodynamics.

Riassunto

Si mostra che, in una teoria dell’elettrodinamica classica precedentemente sviluppata, in cui ogni elettrone classico carico ha il suo proprio campo elettromagnetico (e l’interazione mutua tra una data carica e il campo di un’altra carica costituisce l’interazione elementare della teoria), la condizione che l’energia totale sia definita positiva automaticamente conduce alla forma generalizzata dell’equazione del moto di Lorentz-Dirac per le cariche. Ciò avviene senza la presenza di autointerazioni dirette, perciò la teoria è finita e consistente senza bisogno di tecniche di rinormalizzazione all’infinito. La dimostrazione che questo nuovo formalismo dell’elettrodinamica classica conduce alla stessa classe di equazioni del moto a cui conduce la teoria rinormalizzata di Maxwell-Lorentz (senza infiniti da un criterio di energia interna definita positiva) suggerisce che un tentativo di quantizzare il nuovo formalismo potrebbe condurre a una migliore formulazione dell’elettrodinamica quantica.

Резюме

Мы показываем, что в ранее развитой теории классической электродинамики, в которойкащбый заряженный классический электрон обладает собственным электромагнитным полем (и взаимодействие между данным зарядом и полем другого заряда составляет элементарное взаимодействие этой теории), требование положительно определенной полной энергии автоматически приводит к обобщенной форме уравнения Лорентца-Дирака для движения зарядов. В этой теории отсутствуют само-взаимодействия, поэтому эта теория является конечной и не требует перенормировок. Доказательство того факта, гто этот новый формализм классической электродинамики приводит к тем же уравнениям движения, как и перенормированная теория Максвелла-Лорентца (без бесконечностей, исходя из критерия положительно определенной внутренней энергии), свидетельствует о том, что попытка квантования нового формализма может дать лучшую формулировку квантовой электродинамики.

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References

  1. D. Leiter:Ann. of Phys.,51, 561 (1969);Lett. Nuovo Cimento,3, 101, 347 (1970);Journ. of Phys. A,3, 89 (1970); also see the related work (Comment on a new equation of motion for classical charged particles), Phys. Rev. D, Comments and Addenda Section,6, 2292 (1972);J. Huschilt, W. E. Baylis, D. Leiter andG. Szamosi:Phys. Rev. D,7, 2844 (1973).

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  2. See pages 567 and 568 of the first reference in footnote (1) above.

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  3. See pages 570 thru 573 of the first reference in footnote (1) above, and also see, for comparison to the radiation process in Wheeler-Feynman theory,D. Leiter:Amer. Journ. Phys.,38, 207 (1970).

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  4. Or course reference should be made to the new electrodynamic formalism recently developed byF. Rohrlich (Classical Charged Particles, Chap. 7 (Reading, Mass., 1965), p. 188). Such a formalism is also self-consistent and finite, and also is a candidate for an attempted second quantization (or at the very least could be considered as the proper classical correspondence limit of conventional renormalized QED). It is useful to point out some formal differences between Rohrlich’s theory and the author’s. While we haveN particlesand N Maxwell fields (one for each particle) as dynamic variables,Rohrlich adds onto the time-symmetric Fokker action principletwo field-dynamic variables \(\bar F_{\mu \nu } \) andF μv (+), in such a manner that the time-symmetric, infinite self-interactions are effectively decoupled from the associated equations of motion. Then by imposing physical boundary conditions, asymptotically, he recovers the conventional Lorentz-Dirac equation of motion, without infinite renormalizations necessary. This is a clever and viable formalism, but unlike the author’s, has characteristic terms in the action, similar to Fokker time-symmetric theory, mixed in with two additional dynamic-field variables. Hence, while a canonical second quantization of the author’s theory might proceed along conventional lines, to second-quantize Rohrlich’s would probably require some kind of hybrid approach involving a mixture of Feynman-Hibbs path integral techniques for the Fokker-like elements and a canonical quantization for the field elements. However, our formalism is similiar to Rohrlich’s in that the requirement of positive-definite total energy leads us to the fact that we need to specify that the particle equations of motion must obey α (K)μ →0, τ(K)→∞ (if α≠1/2). This is because the «runaway solutions» can be associated with the fact that the «Schott energy» can act as a negative energy sink which can feed the kinetic energy of the particles, while still conserving the total energy. In any case, our theory does not contradict the Rohrlich theory, but merely stands (with the Rohrlich and Wheeler-Feynman theory) as a possible self-consistent candidate for second quantization, and since it does not involve any Fokker-like time-symmetric interactions in its action principle, seems to be compatible with canonical second quantization in a similiar manner as Maxwell-Lorentz theory.

  5. See footnote (2) above. Because of the division byN−1 one might be tempted to call (16) the total coupled radiation field energy per particle in the limit of very largeN (N≥2).

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  6. For an excellent discussion of this boundary condition see Rohrlich’s book, quoted in footnote (4) aboveF. Fohrlich (Classical Charged Particles, Chap. 7 (Reading, Mass., 1965), pages 134–194. This boundary condition on the particle equations of motion will prevent the nonpositive-definite Schott energy inE (α)total from causingE (α)total to be able to take on possible negative conserved values.

  7. See footnote (6) aboveF. Rohrlich (Classical Charged Particles, Chap. 7 (Reading, Mass., 1965) (note that we use the metric signature (1,-1,-1,-1)).

  8. In ref. (1) above, λ was chosen on the weaker grounds of direct comparison of the general equation of motion to that of the Lorentz-Dirac equation (presumably obtained from some other theoretical source, or else obtained «empirically»). This work shows that there is an internal criterion by which we could have obtained thesame λ without any outside information or reference to previous knowledge of the form of the Lorentz-Dirac equation.

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  9. In Maxwell-Lorentz theory, radiation reaction comes from the finite remainder of the self-interaction, after renormalization is performed; in Wheeler-Feynman theory, it is due the interference effects of a completely absorbing universe on a time-symmetric Fokker type of theory; in Rohrlich electrodynamics, it is due to the interference effects of the\(\bar F_{\mu \nu } \) andF μv (+) fields on the time-symmetric Fokker theory, when the proper asymptotic boundary conditions are imposed.

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Supported by National Research Council of Canada.

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Leiter, D. The Lorentz-Dirac equation and positive-definite energy in classical electrodynamics. Nuovo Cim B 23, 391–401 (1974). https://doi.org/10.1007/BF02723646

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  • DOI: https://doi.org/10.1007/BF02723646

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