Originally posted by heusdens
I did not hear before that Einstein thought that space was ether.
Here some on Einstein's idea and frustration on the gravitational ether. Einstein wanted a kinetic mechanism:
In a letter to Lorentz of 17 June 1916, Einstein wrote:"I agree with you that the general relativity theory admitsof an ether hypothesis as does the special relativity theory. But this new ether theory would not violate the principle of relativity. The reason is that the state [...metric tensor] = Aether is not that of a rigid body in an independent state of motion, but a state of motion which is a function of position determined through the metrical phenomena."
Albert Einstein, in an address (Ether and the Theory of Relativity) delivered on May 5th, 1920, in the University of Leiden: "It is only with reluctance that man's desire for knowledge endures a dualism of this kind. How was unity to be preserved in his comprehension of the forces of nature? Either by trying to look upon contact forces as being themselves distant forces which admittedly are observable only at a very small distance and this was the road which Newton's followers, who were entirely under the spell of his doctrine, mostly preferred to take; or by assuming that the Newtonian action at a distance is only apparently immediate action at a distance, but in truth is conveyed by a medium permeating space, whether by movements or by elastic deformation of this medium. Thus the endeavour toward a unified view of the nature of forces leads to the hypothesis of an ether. This hypothesis, to be sure, did not at first bring with it any advance in the theory of gravitation or in physics generally, so that it became customary to treat Newton's law of force as an axiom not further reducible. But the ether hypothesis was bound always to play some part in physical science, even if at first only a latent part." (full text: http://www.cfpf.org.uk/articles/scientists/einstein.html )
Ludwik Kostro quotes Einstein who said in 1930 (L.Kostro, 1988, p.239, “Einstein and the ether”): "[…] that now it appears that space will have to be regarded as a primary thing and that matter is derived from it, so to speak, as a secondary result. Space is now having its revenge, so to speak, and is eating up matter".
Einstein didn't found although the picture how a mechanical (kinetical) gravitational system could work, and in next text you will feel his frustration and dissapointment. He knew ... but could not express it.
Einstein in The Evolution of Physics (1938): "The Galilean relativity principle is valid for mechanical phenomena. The same laws of mechanics apply to all inertial systems moving relative to each other. Is this principle also valid for nonmechanical phenomena, especially for those for which the field concepts proved so very important? All problems concentrated around this question immediately bring us to the starting point of the relativity theory.
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Is the ether carried with [a] room as the air [is]? Since we have no mechanical picture of the ether it is extremely difficult to answer this question. If the room is closed, the air inside is forced to move with it. There is obviously no sense in thinking of ether in this way, since all matter is immersed in it and it penetrates everywhere. No doors are closed to ether. The 'moving room,' now means only a moving CS [coordinate system] to which the source of light is rigidly connected. It is, however, not beyond us to imagine that the room moving with its light source carries the ether along with it just as the sound source and air is carried along in the closed room. But we can equally well imagine the opposite: that the room travels through the ether as a ship through a perfectly smooth sea, not carrying any part of the medium along but moving through it. In our first picture, the room moving with its light source carries the ether. An analogy with a sound wave is possible and quite similar conclusions can be drawn. In the second, the room moving with its light source does not carry the ether. No analogy with a sound wave is possible and the conclusions drawn in the case of a sound wave do not hold for a light wave. These are the two limiting possibilities. We could imagine the still more complicated possibility that the ether is only partially carried by the room moving with its light source. But there is no reason to discuss the more complicated assumptions before finding out which of the two simpler limiting cases experiment favors
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Every attempt to explain the electromagnetic phenomena in moving Coordinate Systems (CS) with the help of the motion of the ether, motion through the ether, or both these motions, proved unsuccessful.
Thus arose one of the most dramatic situations in the history of science. All assumptions concerning ether led nowhere! The experimental verdict was always negative. Looking back over the development of physics we see that the ether, soon after its birth, became the 'enfant terrible' of the family of physical substances.
First, the construction of a simple mechanical picture of the ether proved to be impossible and was discarded. This caused, to a great extent, the breakdown of the mechanical point of view.
Second, we had to give up hope that through the presence of the ether-sea one CS would be distinguished and lead to the recognition of absolute, and not only relative, motion.
This would have been the only way, besides carrying the waves, in which ether could mark and justify its existence. All our attempts to make ether real failed. It revealed neither its mechanical construction nor absolute motion. Nothing remained of all the properties of the ether except that for which it was invented, i.e., its ability to transmit electromagnetic waves. Our attempts to discover the properties of the ether led to difficulties and contradictions. After such bad experiences, this is the moment to forget the ether completely and to try never to mention its name. We shall say: our space has the physical property of transmitting waves, and so omit the use of a word we have decided to avoid.
The omission of a word from our vocabulary is, of course, no remedy. Our troubles are indeed much too profound to be solved in this way!"
Einstein: "Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world. In our endeavour to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and the moving hands, even hears it ticking, but he has no way of opening the case. If he is ingenious he may form some picture of the mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility of the meaning of such a comparison."
QB (after talking with) Kostro: "Einstein's 4-dimensional ether, if we wish to call it so, cannot provide the same natural causal explanations which, on the contrary, could be supplied by the introduction of a physical "fluid", filling up the whole 3-dimensional space. The action, and properties, of this universal medium could, in principle, rationally explain all physical phaenomena by means of a simple mechanical analogy (in which, for instance, a force can be interpreted only as a vis a tergo, a field as a perturbation of the space, etc.). Einstein's ether, instead, cannot be thought of but in four dimensions, which means that time must be included in the structure of "space" itself (which is in fact more properly called space-time). This circumstance implies that it is absolutely impossible for the human mind to make an intuitive image of it, and to give any simple meaning for instance to expressions like: "dynamical ether", which would have, vice versa, an easy interpretation with respect to a 3-dimensional fluid ether. As a matter of fact, an ether "moving" with respect to what time?
