In 1920 Albert Einstein stated [1]:
page 16: But on the other hand there is a weighty argument to be adducted in favor of the ether hypothesis. To deny the ether is ultimately to assume that empty space has no physical quality whatever. The fundamental facts of (quantum) mechanics do not harmonize with this view.
page 23: Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense.
The above statement is duplicated also by a documentary movie footage [2,3]
Reference:
[1] A. Einstein, Sidelights on Relativity, translated by: G. B. Jeffery and W. Perret, Methuen & Co. London, (1922); republished unabridged and unaltered: Dover, New York, (1983), pp. 16, 23. (picture of the book and pages)[2] Online movie of Einstein's statement about the Aether (1920) https://youtu.be/EtWfLQbJ_To
[3] A. Einstein, Documentary movie footage:
- High resolution (35 MB)
- Medium resolution (834 KB)
- Low resolution (232 KB)
Comments: In his articles in 1905 Einstein did not fully rejected the Ether. He only suggested a mathematical treatment of the problem. In 1920, after he developed the General relativity, he arrived to the conclusion that the ether should exist. This fact is of enormous importance, when citing the contributions of Albert Einstein. However, the textbooks of contemporary physics miss this fact and cite only the Einstein's articles from 1905.
The overthrowing of the Ether concept by the contemporary Physics relies on a very weak argument - the data interpretation of the Michelson-Morley experiment. The later provided more accurate experiments and the reanalysis of the original Michelson-Morley data shows that it has been inconclusive. It is the methodology, which is wrong and this is now confirmed theoretically and experimentally. In a few words, the wrong interpretation of Michelson-Morly and other similar experiments is a result of effect found and recognized by R. R. Hatch (a pioneer in GPS system): the effect of Doppler shift is canceled by the relativistic dependence of the clock rate. In order to avoid this effect, the experiment for detection of the velocity dependence of the speed of light must include a light chopping. A laboratory experiment arranged in a such way is able to detect the Earth motion through space. First sets of such experiments is provided by Stefan Marinov in 1973, 1976 and 1984. The measured velocity is the velocity of the Earth and solar system rotation around the centre of the Milky Way. This experiments defy the postulate of relativity formulated by Einstein, but opens the door for deeper understanding about the physical vacuum and what is behind the space-time.