Stuart Hameroff, an anaesthetist at the University of Arizona, and Roger Penrose, a mathematician from the University of Cambridge, have raised many of the limitations of the theories above. In particular they argue that they cannot fully explain the observed features of consciousness.
The quantum processes theory put forward by Hameroff and Penrose is based upon the principle that there are two levels of explanation in physics: the familiar classical level used to describe large-scale objects and the quantum level used to describe very small events at the subatomic level.
At the quantum level superimposed states are possible, that is, two possibilities may exist for any event at the same time, but at the classical level either one or the other must exist. Hameroff and Penrose propose that consciousness arises from tiny tube-like structures made of proteins that exist in all the cells in the body, including brain cells, and act as a skeleton that allows cells to keep their shape. They propose that these small structures are the site of quantum processes in the brain, due to their structure and shape. They argue that consciousness is thus not a product of direct brain cell to brain cell activity, but rather the action of subatomic processes occurring in the brain.
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