"Still hoping that this thread will attract interactive exchange with those who know something about the foundations of quantum theory ..."
OK Tom, I'll bite. Hardy's Abstract states that:
"This work provides some insight into the reasons why quantum theory is the way it is. For example, it explains the need for complex numbers..."
Elsewhere in these discussions, I have pointed out that complex numbers, arising from the introduction of Fourier Transforms into QM, are not in fact NEEDED at all. They are merely sufficient. The unmeasurable phase of the Fourier Transform is what provides the continuous transform between "pure states" (Axiom 5). But that is also unnecessary, since the Fourier Transform itself is unnecessary.
The Fourier Transform, combined with the summation of the squared real and imaginary parts, is algebraically identical to a filter-bank that computes classical probabilities by merely counting discrete detections. In other words, it forms a histogram, which is why probabilities appear at all.
Let me restate this more bluntly:
Histograms are used to "measure" probability distributions.
Physicists have unwittingly fabricated a mathematical structure for quantum theory, that is identical to a histogram. Consequently, the theory only produces descriptions of probability distributions of measurements, rather than specific measurements, as in classical theories, which do not construct histograms.
Consider a purely classical analogy:
If you created a frequency modulated radio signal, with discrete states, (frequency shift keying) and then attempted to characterize those states via Fourier Transforms, you would encounter all the same problems that physicists have encountered in QM. That is why transforms are not used to "measure" such signals. Instead, a mathematical sturcture that actually measures the frequency, rather than the probability (histogram) of the frequency is used, to characterize the states, and thus demodulate the signal.
Rob McEachern