Introduction In psychotherapy, the object of study is not directly perceptible and material, but involves human mind complexity and specific content Objectives In psychotherapeutic relationship we propose a method to inspect by deduction non-conscious mind, patient hidden mood, hate, affectivity. Aims The aim of this work is using a modern physics research method in psychotherapy, in order to focus on what is not directly perceptible in clinical practice. Methods We can examine, instead of 'inductive method”, the 'deductive method”, adapted from physics theoretical approach. We have taken into consideration 'Human Birth Theory”, formulated in 1971 by psychiatrist Fagioli. The author conceived the beginning of human life as a neuropsyche reaction to light. Given the intrauterine dark, Fagioli deducted that brain at birth are activated by 'the absolutely new stimulus”, light. He also deducted 'vitality” and 'capability to imagine” as non-conscious mind features. We have checked recent neurobiological data in literature. Results Functional maturation of 'subplate zone”, light-inducted Immediate Early Genes activation, SATs variations, from foetus to newborn, retina instant activation by photon, 'viability” support Fagioli’s theory. Conclusions In relativistic physics and quantum field theory, deduction is finalised to discover hidden processes, in order to know the primum movens, not perceptible. In psychodynamic psychotherapy, the object par excellence is not just brain, like in neurology, but psyche. Its content is not directly knowable, but can be known also by deductive method, involving intuition, together perception of patient. In psychotherapy physics method can be applied, to discover the non-conscious thought, previous to pathological behaviour. Clinical examples can be reported.