Satosi Watanabe (渡辺 慧, Watanabe Satosi, 26 May 1910 – 15 October 1993) was a theoretical physicist. He studied various topics, such as the time reversal of quantum mechanics, pattern recognition, cognitive science, and the concept of time. He was the first physicist to show clearly that quantum probability theory is time-asymmetric (irreversible; non-invariant under time reversal), and reject the conventional analysis of the time reversal of probability laws. He developed the Double Inferential Vector Formalism (DIVF), later known as the Two-state vector formalism (TSVF), which is sometimes interpreted as contradicting his proof of time-asymmetry, but this is a misunderstanding. He also proposed the Ugly duckling theorem.