Perhaps the most bizarre quantum feature is the effect called superposition that implies that quantum particles can exist in multiple spatial locations. Such quantum superposition states can end when out of each multiplicity of the possible states the system selects one definite state or spatial location. A number of experiments in the early 20th century demonstrated that quantum superpositions persisted until they were observed or measured by an experimentalist (observer). If a machine measured a quantum system, the results appeared to remain in superposition within the machine until actually viewed by experimenters.
To illustrate this paradox and the apparent absurdity of the notion, Erwin Schrödinger in 1935 described his celebrated thought experiment known as Schrödinger's cat. In this example, a cat is placed in a box with a vial of poison. Outside the box, a quantum event (e. g., passage/not passage of a single photon through a halfsilvered mirror) is causally connected to the release of the poison inside the box. Since the photon is a quantum object in a superposition state, it both passes and does not pass through the mirror. Hence the poison is both triggered and not triggered. Therefore, by quantum logic, the cat must be both dead and alive until the box is opened and the cat observed. (Analogous to quantum logic, superposition of mental events is commonplace, further suggesting that the mind is a quantum system. Cognitively, we are simultaneously prepared for the cat being alive and prepared for the cat being dead until we open the box.) At the moment the box is opened, the system chooses either to reveal a dead cat or a live cat. Therefore, consciousness essentially selects reality. The precise choice in any given quantum collapse experiment was believed to be probabilistic, an idea Einstein found unsettling by proclaiming in a famous statement that: “God does not play dice with the universe.”
Today the generally accepted view is that any interaction of a quantum superposition state with the classical environment causes decoherence. Due to these difficulties many physicists maintain that quantum theory is incomplete and that other approaches to the problem of collapse of the quantum wave function need to be found. In his 1999 paper, Stapp addresses potential causal interactions, raising possibility that: “conscious intentions of a human being can influence the activities of his brain”. Stapp further argues that the probabilities for eigenstates after collapse can be mentally influenced and that conscious mental events are assumed to correspond to quantum collapses of superposition states at the level of macroscopic brain activity.
More recently, Penrose has claimed that the underlying reality itself, namely the fundamental space-time geometry, actually bifurcates during the superposition process. This is similar to the multiple-worlds view except the separations are unstable and hence they rapidly reduce to a single, undivided reality. Classical noncomputability is a key feature of conscious processes, which may also elevate our mental processes above that of mechanistic determinism that appears grossly inadequate. Penrose claims that the phenomenon of quantum collapse can explain the features of consciousness since the spontaneous wave function collapse is what distinguishes our thought processes from the behaviour of completely deterministic classical computers. According to Penrose, consciousness involves a time-ordered series of quantum-state reductions corresponding to individual thoughts. Although such ideas are controversial, the fact that quantum theory is being applied successfully to a new kind of computing (called quantum computing) where the collapse of multiple quantum possibilities to definite classical states is the key element lends credence to quantum approaches to consciousness.
