Page:Das Prinzip der Relativität und die Grundgleichungen der Mechanik.djvu/1

The Principle of Relativity and the Fundamental Equations of Mechanics;

by Max Planck.

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The "principle of relativity" recently introduced by H.A. Lorentz^[1] and in even more general form by A. Einstein^[2], states that of two reference frames (x, y, z, t) and (x ', y', z ', t') connected by the relations

${\begin{cases}x'={\frac {c}{\sqrt {c^{2}-v^{2}}}}(x-vt),\ y'=y,\ z'=z,\\\\t'={\frac {c}{\sqrt {c^{2}-v^{2}}}}\left(t-{\frac {v}{c^{2}}}x\right)\end{cases}}$

1)

(c is the speed of light in vacuum), none can be used with greater justification than the other one as regards the fundamental equations of mechanics and electrodynamics, i.e., none of them can be called as "at rest" with greater justification than the other one. This implies (if this should be verified in general) such a great simplification of all the problems of electrodynamics of moving bodies, that the question of its admissibility deserves to be put to the forefront of any theoretical research in this field. Of course, this question already seems to be settled by the recent important measurements by W. Kaufmann^[3] in a negative sense, so any further investigation would be superfluous. However, in view of the complicated theory of these experiments I would not completely exclude the possibility, that the principle of relativity on closer elaboration might just prove compatible with the observations. Also as regards the concerns

1. H. A. Lorentz, Versl. Kon. Akad. v. Wet. Amsterdam 1904, S. 809.
2. A. Einstein, Ann. d. Phys. (4) 17, 891, 1905.
3. W. Kaufmann, Sitzungsber. d. preuß. Akad. d. Wiss. 1905, S. 949; Ann. d. Phys. (4) 19, 487, 1906.