Quote:
|
Originally Posted by Ken G
That's an interesting insight, although at present I don't know what Einstein meant about a local ether. It surprises me that he didn't want light to propagate through nothing, in the sense that it seems to me a crucial element of relativity is that if two objects in empty space communicate via light, then the only relevant effect is the relative speed between the objects, not the speed of either relative to the space they are in. The former is unique, the latter is observer-dependent. In this light, the "nothingness" of space is seen as an advantage, since it explains why there is only one velocity of relevance, rather than two.
|
Lifted from John Baez's site:
"according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [. . .] cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position." Einstein 1920
In other words, you cannot have gravitational lensing in "empty space" unless the space has optical properties (i.e. an index of refraction) at each position in space, so that light can travel slower in more dense locales and faster in sparser ones. By 1924, Einstein was sure that the EM ether and his GR gravitational ether were one and the same, but quantum theory was in its infancy and the quantum vacuum (a seething Zero Point Energy field filled with virtual particle-antiparticle pairs) would have been considered a pretty crazy idea. His idea for a GR ether was decades ahead of the rest of physics.