Comment: A skeptic of quantum theory explains his misgivings

H.J. Groenewold

Greg Gbur

George C. Knee, Erik M. Gauger, G. Andrew D. Briggs +1 more

A recent paper by Souza, Oliveira and Sarthour (SOS) reports the experimental violation of a Leggett–Garg (LG) inequality (sometimes referred to as a temporal Bell inequality). The inequality tests for quantum mechanical superposition: if the inequality is violated, the dynamics cannot be explained by a large class of classical theories under the heading of macrorealism. Experimental tests of the LG inequality are beset by the difficulty of carrying out the necessary so-called 'non-invasive' measurements (which for the macrorealist will extract information from a system of interest without disturbing it). SOS argue that they nevertheless achieve this difficult goal by putting the system in a maximally mixed state. The system then allegedly undergoes no perturbation during their experiment. Unfortunately, the method is ultimately unconvincing to a skeptical macrorealist and so the conclusions drawn by SOS are unjustified.

Holger Lyre

Gregory R. Mulhauser

Two principle concerns prompt some theorists to link quantum mechanics and theories of mind or theories of consciousness. On the one hand, it is commonly thought that conscious minds play some important role in processes of quantum measurement and that any good theory of mind ought to explain how a mind can play such a role. On the other hand, a few people think that the framework of classical physics is not, by itself, sufficiently powerful to explain the myriad remarkable properties of minds and that a good explanation must rely on some special features of quantum mechanics. Usually, these features include either state vector reduction-the collapse of the wave function-or special capabilities, often computational or super-computational ones, allegedly displayed by physical substrates while existing in hypothesised coherent states of linear superposition. Two questions summarise the author's misgivings about both the above motivations for linking quantum mechanics and theories of mind. First, does the process of quantum measurement really require a conscious observer? Second, does quantum mechanics underwrite any special effects in, say, intraneuronal protein lattices, which could play a role in instantiating consciousness in biological systems? It turns out that the particular character of the negative answer suggested for the first question also prompts a negative answer for the second. He summarises these negative answers after describing briefly some popular attempts to forge quantum theories of mind.