Satosi Watanabe 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, and reject the conventional analysis of the time reversal of probability laws. He developed the Double Inferential Vector Formalism, later known as the Two-state vector formalism, which is sometimes interpreted as contradicting his proof of time-asymmetry, but this is a misunderstanding. He also proposed the Ugly duckling theorem.
In Japan, he worked at the Physical and Chemical Research Institute at Tokyo Imperial University as an assistant professor, and as a physics professor at Rikkyo University. In 1950, he left for the United States. His argument that quantum mechanics is time-asymmetric is repeated in a number of his papers. It is informal but quite correct, as a more formal proof confirms. This result means that physicists have used the wrong transformation of probability laws to represent time reversal, and the popular claims that quantum mechanics is time reversal invariant are invalid. Watanabe's argument has not been accepted by physicists or philosophers however. The assumption that quantum mechanics is time symmetric on the basis of invalid conventional proofs is almost universal in the literature on time in physics to this day. He developed the Double Inferential Vector Formalism, later known as the Two-state vector formalism. The DSVF/TSVF is often interpreted as a time-symmetric interpretation of quantum mechanics. However Watanabe was quite clear that the normal physical theory of quantum mechanics that holds for real physics is time-asymmetric. He consequently rejected the conventional view that physical time asymmetry is only explained by asymmetric boundary conditions on the universe, and claimed it is a law-like feature of quantum physics. Time-symmetric interpretations of quantum mechanics were first suggested by Walter Schottky in 1921, and later by several other scientists. Watanabe proposed that information given by forwards evolving quantum states is not complete; rather, both forwards and backwards evolving quantum states are required to describe a quantum state: a first state vector that evolves from the initial conditions towards the future, and a second state vector that evolves backwards in time from future boundary conditions. Past and future measurements, taken together, provide complete information about a quantum system. Watanabe's work was later rediscovered by Yakir Aharonov, Peter Bergmann and Joel Lebowitz in 1964, who later renamed it the Two-state vector formalism. In 1956, he became a researcher at the IBM Watson Laboratory and started to build his own information theory based on quantum mechanics. He taught at Yale University and the University of Hawaii, became chairman of the International Time Academy, and was the Vice President of International Philosophy Academy. On October 15, 1993, he died in Tokyo.
