Einstein Derived Spacetime From... Spacetime

Einstein derived spacetime from the constancy of the speed of light, but where did Einstein take the constancy from?

http://community.bowdoin.edu/news/20...rs-of-gravity/
"Special relativity is based on the observation that the speed of light is always the same, independently of who measures it, or how fast the source of the light is moving with respect to the observer. Einstein demonstrated that as an immediate consequence, space and time can no longer be independent, but should rather be considered a new joint entity called "spacetime."

There was no "observation" supporting the constancy of the speed of light - on the contrary, in 1887 the Michelson-Morley experiment had proved unequivocally that the speed of light is variable, as predicted by Newton's emission theory of light. Einstein took the constancy of the speed of light from the Lorentz transformation equations, which are equivalent to spacetime. In other words, Einstein derived spacetime from spacetime:

https://en.wikipedia.org/wiki/Lorentz_ether_theory
Albert Einstein: "...it is impossible to base a theory of the transformation laws of space and time on the principle of relativity alone. As we know, this is connected with the relativity of the concepts of "simultaneity" and "shape of moving bodies." To fill this gap, I introduced the principle of the constancy of the velocity of light, which I borrowed from H. A. Lorentz's theory of the stationary luminiferous ether..."

There was a small problem - the constancy of the speed of light was obviously nonsense - but that could not stop the genius:

http://www.aip.org/history/exhibits/...relativity.htm
John Stachel: "But this seems to be nonsense. How can it happen that the speed of light relative to an observer cannot be increased or decreased if that observer moves towards or away from a light beam? Einstein states that he wrestled with this problem over a lengthy period of time, to the point of despair."

Pentcho Valev

That the speed of light is independent of the speed of the observer is an obvious idiocy and yet Poincaré did not protest, even though he did not accept it:

http://www.jstor.org/stable/3653092
Olivier Darrigol, The Mystery of the Einstein-Poincaré Connection: "It is clear from the context that Poincaré meant here to apply the postulate [of constancy of the speed of light] only in an ether-bound frame, in which case he could indeed state that it had been "accepted by everybody." In 1900 and in later writings he defined the apparent time of a moving observer in such a way that the velocity of light measured by this observer would be the same as if he were at rest (with respect to the ether). This does not mean, however, that he meant the postulate to apply in any inertial frame. From his point of view, the true velocity of light in a moving frame was not a constant but was given by the Galilean law of addition of velocities."

Hypocrisy? Yes, in a sense. The idiocy was an implication from the Lorentz transformation equations, and Poincaré was not ready to abandon them. Yet he was very close to the truth:

http://www.marxists.org/reference/su...r/poincare.htm
Henri Poincaré: "Lorentz could have accounted for the facts by supposing that the velocity of light is greater in the direction of the earth's motion [c'=c+v : the emission theory's postulate!] than in the perpendicular direction. He preferred to admit that the velocity is the same in the two directions, but that bodies are smaller in the former than in the latter."

Pentcho Valev