Quantum weirdness flips which math describes reality better

Standard quantum mechanics uses complex numbers, and experiments have confirmed complex theory is richer than real-number quantum theory — until you allow causal order itself to be indefinite. Under 'indefinite causal order,' where it's quantum-uncertain which event influences which, real quantum theory produces strictly more correlations than complex quantum theory. The hierarchy completely reverses, suggesting the supremacy of complex numbers isn't fundamental but depends on assuming a fixed arrow of causality.