Penrose and Hameroff
Theoretical physicist Roger Penrose and anaesthesiologist Stuart Hameroff collaborated to produce the theory known as Orchestrated Objective Reduction (Orch-OR). Penrose and Hameroff initially developed their ideas separately, and only later collaborated to produce Orch-OR in the early 1990s. The theory was reviewed and updated by the original authors in late 2013.
Penrose’s controversial argument began from Gödel’s incompleteness theorems. In his first book on consciousness, The Emperor’s New Mind (1989), he argued that while a formal proof system cannot prove its own inconsistency, Gödel-unprovable results are provable by human mathematicians. He took this disparity to mean that human mathematicians are not describable as formal proof systems, and are not therefore running a computable algorithm.
Penrose determined that wave function collapse was the only possible physical basis for a non-computable process. Dissatisfied with its randomness, Penrose proposed a new form of wave function collapse that occurred in isolation, called objective reduction. He suggested that each quantum superposition has its own piece of spacetime curvature, and when these become separated by more than one Planck length, they become unstable and collapse. Penrose suggested that objective reduction represented neither randomness nor algorithmic processing, but instead a non-computable influence in spacetime geometry from which mathematical understanding and, by later extension, consciousness derived.
Originally, Penrose lacked a detailed proposal for how quantum processing could be implemented in the brain. However, Hameroff read Penrose’s work, and suggested that microtubules would be suitable candidates.
Microtubules are composed of tubulin protein dimer subunits. The tubulin dimers each have hydrophobic pockets that are 8 nm apart, and which may contain delocalised pi electrons. Tubulins have other smaller non-polar regions that contain pi electron-rich indole rings separated by only about 2 nm. Hameroff proposes that these electrons are close enough to become quantum entangled. Hameroff originally suggested the tubulin-subunit electrons would form a Bose-Einstein condensate, but this was discredited. He then proposed a Frohlich condensate, a hypothetical coherent oscillation of dipolar molecules. However, this too has been experimentally discredited.
Furthermore, he proposed that condensates in one neuron could extend to many others via gap junctions between neurons, thus forming a macroscopic quantum feature across an extended area of the brain. When the wave function of this extended condensate collapsed, it was suggested to non-computationally access mathematical understanding and ultimately conscious experience, that are hypothetically embedded in the geometry of spacetime.
However, Orch-OR made numerous false biological predictions, and is considered to be an extremely poor model of brain physiology. The proposed predominance of ‘A’ lattice microtubules, more suitable for information processing, was falsified by Kikkawa et al., who showed that all in vivo microtubules have a ‘B’ lattice and a seam. The proposed existence of gap junctions between neurons and glial cells was also falsified. Orch-OR predicted that microtubule coherence reaches the synapses via dendritic lamellar bodies (DLBs), however De Zeeuw et al. proved this impossible, by showing that DLBs are located micrometers away from gap junctions.