It is possible that ether exists according to symmetry of physical world and ether is virtual particle of super light velocity baseing on the formula of restricted relative theory.

Then Einstein, with his special theory of relativity, looked at a whole set of symmetries of Maxwell's equations, which are called special relativity.

In this paper, authors present a derivation of the Lorents transformation by invoking the principle of relativity alone, without the principle of invariance of light speed.