Complex sentence: Einstein radically reformulated the concepts of space and time, and by that removed "absolute space" and thus the luminiferous aether from physics, while Poincaré and Lorentz still adhered to the aether concept, and tried only to modify Newtonian dynamics, not to replace it.
Split into simpler sentences: Einstein radically reformulated the concepts of space and time, and by that removed "absolute space" and thus the luminiferous aether from physics. While Poincaré and Lorentz still adhered to the aether concept, and tried only to modify Newtonian dynamics, not to replace it.