During the 1920s and 1930s physics offers a different view of reality, and psychoanalysis attempts to apply new scientific methods to the study of mind. Sàndor Ferenczi called "utraquism" this similarity method used between disciplines, even very different ones. The application of thermodynamics’ laws in instinct theory is the most explored field of investigation. It was anticipated by Freud in the Wolf Man (1914 ), and later C.G. Jung writes a paper that called the "Psychic energy" (1928), Bernfeld & Feitelberg (1930, 1931) try to prove the existence of the death instinct by the law of entropy, and finally Wilhelm Reich (1934-37, 1948) proposes a theory of energy that allows him to measure libido. All these attempts to apply the rules of physics to the unconscious were doomed to fail, but they pushed the psychoanalytic movement to discuss on the role of psychoanalysis among the sciences.
Keywords: Sàndor Ferenczi, Wilhelm Reich, instinct theory, reductionism, utraquism