“It has been generally believed that only the complex numbers could legitimately be used as the ground field in discussing quantum-mechanical operators. Over the complex field, Frobenius' theorem is of course not valid; the only division algebra over the complex field is formed by the complex numbers themselves. However, Frobenius' theorem is relevant precisely because the appropriate ground field for much of quantum mechanics is real rather than complex.”

— Freeman Dyson

[The threefold way: algebraic structure of symmetry groups and ensembles in quantum mechanics, Jour. Math. Phys., 3, 1962, 1199–1215, https://books.google.com/books?id=nnyNUidX1OMC&pg=PA410] (p. 1200)

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Freeman Dyson 90

theoretical physicist and mathematician 1923

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