The standard formulation of quantum mechanics relies on complex numbers, which include an imaginary part. Physicists have wondered whether this can be considered a form of mathematical convenience, just as complex numbers facilitate calculations in electromagnetism, or not. Marc-Oliver Renou and colleagues now construct a Bell-like inequality which allows the experimental discrimination between predictions of standard quantum physics and of a version of quantum physics that is entirely built without complex numbers. Their result suggests that it is only in multi-party scenarios that such differences become noticeable.
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