Can Quantum Physics Be Used to Explain the Existence of Consciousness?

The answer involves determinism: the theory that humans have free will

Quantum physics formulas over blackboard
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Trying to explain where subjective experiences come from would seem to have little to do with physics. Some scientists, however, have speculated that perhaps the deepest levels of theoretical physics contain the insights needed to illuminate this question by suggesting that quantum physics can be used to explain the very existence of consciousness.

Consciousness and Quantum Physics

One of the first ways that consciousness and quantum physics come together is through the Copenhagen interpretation of quantum physics. In this theory, the quantum wave function collapses due to a conscious observer making a measurement of a physical system. This is the interpretation of quantum physics that sparked the Schroedinger's cat thought experiment, demonstrating some level of the absurdity of this way of thinking, except that it does completely match the evidence of what scientists observe at the quantum level.

One extreme version of the Copenhagen interpretation was proposed by John Archibald Wheeler and is called the participatory anthropic principle, which says that the entire universe collapsed into the state we see specifically because there had to be conscious observers present to cause the collapse. Any possible universes that do not contain conscious observers is automatically ruled out.

The Implicate Order

Physicist David Bohm argued that since both quantum physics and relativity were incomplete theories, they must point at a deeper theory. He believed that this theory would be a quantum field theory that represented an undivided wholeness in the universe. He used the term "implicate order" to express what he thought this fundamental level of reality must be like, and believed that what we are seeing are broken reflections of that fundamentally ordered reality.

Bohm proposed the idea that consciousness was somehow a manifestation of this implicate order and that attempting to understand consciousness purely by looking at matter in space was doomed to failure. However, he never proposed any scientific mechanism for studying consciousness, so this concept never became a fully-developed theory.

The Human Brain

The concept of using quantum physics to explain human consciousness really took off with Roger Penrose's 1989 book, "The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics." The book was written specifically in response to the claim of old school artificial intelligence researchers who believed that the brain was little more than a biological computer. In this book, Penrose argues that the brain is far more sophisticated than that, perhaps closer to a quantum computer. Instead of operating on a strictly binary system of on and off, the human brain works with computations that are in a superposition of different quantum states at the same time.

The argument for this involves a detailed analysis of what conventional computers can actually accomplish. Basically, computers run through programmed algorithms. Penrose delves back into the origins of the computer, by discussing the work of Alan Turing, who developed a "universal Turing machine" that is the foundation of the modern computer. However, Penrose argues that such Turing machines (and thus any computer) have certain limitations which he doesn't believe the brain necessarily has.

Quantum Indeterminacy

Some proponents of quantum consciousness have put forth the idea that quantum indeterminacy—the fact that a quantum system can never predict an outcome with certainty, but only as a probability from among the various possible states—would mean that quantum consciousness resolves the problem of whether or not humans actually have free will. So the argument goes, if human consciousness is governed by quantum physical processes, then it is not deterministic, and humans, therefore, have free will.

There are a number of problems with this, which are summed up by neuroscientist Sam Harris in his short book "Free Will," where he stated:

"If determinism is true, the future is set—and this includes all our future states of mind and our subsequent behavior. And to the extent that the law of cause and effect is subject to indeterminism—quantum or otherwise—we can take no credit for what happens. There is no combination of these truths that seems compatible with the popular notion of free will.

The Double-Slit Experiment

One of the best-known cases of quantum indeterminacy is the quantum double slit experiment, in which quantum theory says that there is no way to predict with certainty which slit a given particle is going to go through unless someone actually makes an observation of it going through the slit. However, there is nothing about this choice of making this measurement which determines which slit the particle will go through. In the basic configuration of this experiment, there is a 50 percent chance the particle will go through either slit, and if someone is observing the slits, then the experimental results will match that distribution randomly.

The place in this situation where humans do appear to have some sort of choice is that a person can choose whether she is going to make the observation. If she does not, then the particle does not go through a specific slit: It instead goes through ​both slits. But that's not the part of the situation that philosophers and pro-free will advocates invoke when they're talking about quantum indeterminacy because that is really an option between doing nothing and doing one of two deterministic outcomes.