Albert Einstein, Philipp Lenard, Hermann Weyl, Ernst Gehrcke

“ When e.g. in an immediately stopped train everything is falling around, then by the common sense one can decide, whether the change of the train's motion or that of the earth is the cause for it. If one additionally thinks, that one cannot say whether we are in rotational motion, or the environment - then one only has to assume the latter, to see that one has to admit superluminal velocities. ”

“ In Einstein's theory like in the older interpretation there is a guidance field that is followed by a body according to the Galilean principle, as long as no forces act on it. The catastrophe happens at the train and not at the church steeple, since the first is thrown out of its path by the molecular forces of the oncoming train, but the church steeple is not. This answer is also completely in agreement with "commons sense", which whole-heartedly agrees that the inertial-tendency of the guidance field (that opposes to the forces) can be seen as a physical reality. ”

“ The planetary motion follows the path that is given by the guidance; while in the old mechanics the motion doesn't comply with the Galilean principle, but is diverted from its path by a special force that was ad-hoc invented by Newton, the "force of gravity". However, according to Einstein, inertia and gravitation constitute a inseparable unity; therefore inertial and gravitational masses must necessarily be the same ”

“ According to Democrit, there exists an absolute "above-below" per se; the real falling direction of a body is composed of its absolute direction and the deviation from it that stems from a physical cause. For example, Democrit could argue against Newton (who sees the fall direction as an unity) in the same way as Lenard against Einstein: If another direction as the true one is installed as the normal direction, then one has to introduce in addition to it and the real deviation, a third fictitious deviation that is everywhere the same and is not connected with matter ”

“ The principle of relativity works with a non-euclidean space, that assumes different properties from place to place and in successive times; so there might be something in space whose conditions are the cause of those different properties, and this something is exactly the aether. ”

“ Such a formulation is impossible, when one really has understood the unity of inertia and gravitation that was called by me the "guidance field". Also inertia, the "Galilean guidance field" that brings a body to fly in a straight line with constant velocity, and which according to Newton-Lenard exists once and for all time without material cause, has according to Einstein its cause in the generating masses. Namely, this neutral basis of gravitation is caused by the collective action of all masses in the universe ”

“ Together with inertial forces, something comes into light which was until now be interpreted as the "geometrical structure": the "guidance field", as something real, as an acting power of shaking force in some cases. ”

“ In Lorentzian electrodynamics it was transformed into a pure geometrical, i.e. a forever solid structure that won't be influenced by matter. In Einstein's special theory of relativity another one took its place, the affine geometric structure. In the general theory of relativity eventually the latter was, as an "affine connection" or "guidance field", transformed back into a state-field of physical reality, that is in effective connection with matter. And therefore Einstein considered it convenient, to reintroduce the old word aether for the completely changed concept ”

“ Between active future and passive past an empty world-area lies, with which I'm neither actively nor passively connected in the instant O. — The stage of reality is not a stationary three-dimensional space in which things are engaged in temporal progression, but a four-dimensional world in which time and space are inseparably connected to each other. This objective world does not happen, but it exists; a four-dimensional continuum, but neither space nor time. ”

“ But second and especially it is completely excluded that matter can uniquely determine the field, if one considers mass, charge, and state of motion as the characteristics of matter. Because one can introduce such an coordinate system into the world, that by the following projection of the world on a four-dimensional Cartesian image space, not only the world channel of one particle, but of all particles assume a simultaneously given form, e.g. ”

“ A thought experiment is only prohibited, when a realization is principally impossible.
Lenard: I think it can be summarized: 1. That it's better if one refuses to proclaim the "rejection of the aether". 2. That I still consider it necessary to restrict the relativity principle to a gravitational principle, and 3., that superluminal velocities are apparently still problematic for the relativity principle ”