"... 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. ..."
http://nl.wikipedia.org/wiki/Ether_(medium)
HOWEVER how does that ether manage a constant lightspeed?
ANSWER; by MASS influence.
Radar reflection timing experiments between Earth and Venus (even Mercury) have learned us that the extra orbital light speed of the radar (reflection) light source, in orbit around the Sun, has an extinction distance which is related to the mass of the planet.
These extinction distances are calculated to be: 70-54 and 21 million km for respectively Earth, Venus and Mercury.
The other Einstein:
In 1954, Einstein wrote to his dear friend M. Besso:
I consider it quite possible that physics cannot be based on the field concept, i.e., on continuous structures. In that case, nothing remains of my entire castle in the air, gravitation theory included, [and of] the rest of modern physics. (in “Subtle is the Lord” by A. Pais, page 467)
Thus, if space on the smallest scale is crystalline, then we may assume space to be based on a “Lattice model”, as opposed to the field concept of space.
HOWEVER:
Today physics stands at the threshold of major discoveries. Growing observational evidence points to the need for new physics.
As a result, efforts to discover new fundamental symmetries, investigations of the limits of established symmetries, tests of the general theory of relativity, searches for gravitational waves, and attempts to understand the nature of dark matter and dark energy are among the main research topics in fundamental physics today.
From: Experimental Tests of General Relativity Slava G. Turyshev Jet Propulsion Laboratory, http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1731v2.pdf
For my own experiment proposals see:
Small Gravity and GR anomalies and Test Proposals
http://bigbang-entanglement.blogspot.com/2006/03/how-small-anomalies-could-influence.html