From the horse's mouth: "There is no doubt, that the special theory of relativity, if we regard its development in retrospect, was ripe for discovery in 1905.

From the horse's mouth: "There is no doubt, that the special theory of relativity, if we regard its development in retrospect, was ripe for discovery in 1905. Lorentz had already recognized that the transformations named after him are essential for the analysis of Maxwell's equations, and Poincaré deepened this insight still further. Concerning myself, I knew only Lorentz's important work of 1895 [...] but not Lorentz's later work, nor the consecutive investigations by Poincaré. In this sense my work of 1905 was independent. [..] The new feature of it was the realization of the fact that the bearing of the Lorentz transformation transcended its connection with Maxwell's equations and was concerned with the nature of space and time in general. A further new result was that the "Lorentz invariance" is a general condition for any physical theory." -- Albert Einstein ---- In "La théorie de Lorentz et le principe de réaction", Poincaré published a paper in which he said that radiation could be considered as a fictitious fluid with an equivalent mass of m = E/ c^2. He derived this interpretation from Lorentz's 'theory of electrons' which incorporated Maxwell's radiation pressure. Plenty of material here: https://en.wikipedia.org/wiki/Relativity_priority_dispute https://en.wikipedia.org/wiki/Relativity_priority_dispute ---- TL;DR: it definitely did not happen in a vacuum. IMHO his contribution is making science happen 1-2 years earlier (which is still a tremendous feat by itself).