Saturday, June 6, 2020

Unending Confusion in the Foundations of Physics

Quantum mechanics is difficult enough without physicists mucking it all up.  Setting aside the problem that they speak in a convoluted language that is often independent of what’s actually happening in the observable physical world, they are sometimes fundamentally wrong about their own physics.

In 2007, a researcher named Afshar published a paper on a fascinating experiment in which he was able to infer the existence of a double-slit interference pattern when thin wires placed where destructive interference would be expected failed to significantly reduce the amount of light passing through.  It was clever and certainly worthy of publication.

But he took it a step too far and stated that the experiment showed a violation of wave-particle complementarity – in other words, he asserted that the photons showed both wave-like behavior and particle-like behavior at the same time.  The first is correct: the existence of interference in the far field of the double-slit indicated the wave behavior.  But the second (the simultaneous particle-like behavior) is not correct, as it depended on his claim that which-way information, which inherently does not and cannot exist in a superposition over two slits, exists retroactively through a later measurement.

I feel like Afshar can be excused for this mistake, for two reasons.  First, the mistake has its origins in a very reputable earlier reference by famed physicist John Wheeler.  Second, his experiment was new, useful, and elucidating for the physics community.  Having said that, the mistake represents such a fundamental misunderstanding of the very basics of quantum mechanics that it should have been immediately and unambiguously refuted – and then brought up no more.  But that’s not what happened.  What happened is this:

·         The paper is cited by over a hundred papers, very few of which refute it.
·         Among those that refute it, several refute it incorrectly.
·         Those that refute it correctly use over a hundred pages and several dozen complicated quantum mechanics equations.  Their inability to address and solve the problem clearly and succinctly only obfuscates what is already an apparently muddled issue.

Here is my two-page refutation of Afshar.

How exactly are physics students ever going to understand quantum mechanics when the literature on the foundations of physics is so confused and internally inconsistent?

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