(Classical physics was formulated entirely with real numbers. Could quantum mechanics have even been formulated without complex numbers? What could it possibly look like? Isn’t the fact that complex numbers were created long before quantum mechanics required it, another example of the unreasonable effectiveness of mathematics?

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**The Outer Limits of Reason****Noson Yanofsky**. MIT Press, Cambridge, MA and London, England, 2013 -

**Reviewed by Michael Barr**, The American Mathematical Monthly, Vol. 121, No. 7 (August–September), pp. 658-660)