Query: What quality of the theory of relativity did Popper believe made it proper science?
Context: Popper puzzled over the stark contrast between the non-scientific character of Freud and Adler's theories in the field of psychology and the revolution set off by Einstein's theory of relativity in physics in the early 20th century. Popper thought that Einstein's theory, as a theory properly grounded in scientific thought and method, was highly "risky", in the sense that it was possible to deduce consequences from it which were, in the light of the then-dominant Newtonian physics, highly improbable (e.g., that light is deflected towards solid bodies—confirmed by Eddington's experiments in 1919), and which would, if they turned out to be false, falsify the whole theory. In contrast, nothing could, even in principle, falsify psychoanalytic theories.