Abstract
UNDER this title, in NATURE of April 13, p. 587, Prof. M. Born and K. Fuchs gave some relations between the total and a relative momentum vector of a system of two free particles. They only define the magnitude, not the direction of their relative momentum vector. I believe things become clearer by the following statement. Let Va, Wa (a = 0, 1, 2, 3) be (1 + 3)-dimensional velocity time-space vectors of the particles (V2 = W2 = c2), and m1, m2 their scalar masses. Their individual energy-momentum vectors being ia = m1Va and ja = m2Wa we may define the total energy-momentum vector by the relative energy-momentum vector by These definitions entail two identities which are equivalent to equations (4), (5), (6) of Born and Fuchs.
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References
Physica, Ned. T. Natuurk., 7, 330 (1927). Fokker, “Relativiteits-theorie” (Groningen: Noordhoff, 1929).
Physica, Ned. T. Natuurk., 1, 35 (1921).
Nuyens, M., Physica, Ned. T. Natuurk., 9, 181 (1929).
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FOKKER, A. Mass Centre in Relativity. Nature 145, 933 (1940). https://doi.org/10.1038/145933a0
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DOI: https://doi.org/10.1038/145933a0
