You are thinking of specific relativity. He didn't plagiarize the theory of specific relativity either because nobody had suggested it. Poincaré's idea of relat

You are thinking of specific relativity. He didn't plagiarize the theory of specific relativity either because nobody had suggested it. Poincaré's idea of relativity relied on the existence of a Luminiferous aether which was disproved in the early 20th century.