(Neue Zürcher Zeitung NZZ, October 12, 2024)

Nils Althaus and Mirko Bischofberger

The sixth and final installment of our “Walks Through Consciousness” series explores some of the strangest theories of consciousness.

In the subatomic world, the strange laws of quantum mechanics take over. An electron, for example, can be in two places at once—a state physicists call “superposition.” But try to measure the particle in an experiment, and it suddenly appears in just one place. The act of measurement itself causes the superposition to collapse, and the particle instantly settles on a single location.

A new theory proposes that these ghostly processes may be responsible for consciousness. Its authors include prominent figures such as Hartmut Neven, who builds quantum computers for Google, and Christof Koch, a leading consciousness researcher. They suggest that conscious experience arises whenever a superposition forms somewhere in the brain.

Quantum theories of consciousness have always been speculative. The best-known version was proposed in 1989 by Nobel Prize–winning physicist Roger Penrose. In a sense, his theory was the reverse of the new one: Conscious experience arises whenever an existing superposition in the brain collapses. The idea drew plenty of criticism. The brain is too warm, wet, and noisy to sustain such quantum states for long enough, argued Max Tegmark, another prominent physicist.

Philosopher David Chalmers raised a more fundamental objection: Quantum theories suffer from the same weakness as conventional theories of consciousness. They fail to explain how something physical can give rise to subjective experience. Both objections could also be leveled at Neven and Koch’s new proposal.

So why reach for quantum mechanics at all? Isn’t consciousness simply what happens when certain parts of the brain become active? Mainstream accounts of consciousness may initially seem simpler and more plausible. But appearances are deceiving: They, too, have some decidedly strange implications.

Functionalism Can Explain a Lot

The theory that comes closest to our everyday understanding treats consciousness as a kind of software running on biological hardware—the brain. Like computer software, consciousness receives inputs, such as sensory impressions, combines them with existing information, and produces outputs, such as behavior.

This view, known as functionalism, accommodates the fact that consciousness seems possible across very different brain architectures. Dogs, parrots, and humans all appear to be conscious despite their very different neurological hardware. The same is true of people with epilepsy who had an entire cerebral hemisphere removed as children. Their inner lives seem little different from those of healthy people—apparently, the software can run on just half the hardware.

Functionalism can explain a lot. But it also implies that nation-states such as Switzerland might be conscious. After all, the features that make brains special can also be found in nation-states. They, too, receive inputs, process information, and produce outputs. Ask neuroscientists and philosophers which functional features distinguish the human brain, and they often point to its ability to process complex information, respond flexibly and purposefully to its environment, and form a representation of itself.

Switzerland does all of those things. Its processes may move considerably more slowly—depending on the canton—but there is no obvious reason consciousness could not run on slower hardware. After all, the same software can run on processors of different speeds.

Our commonsense understanding of consciousness therefore suggests that nation-states might possess it—a decidedly strange idea. The notion that quantum-mechanical superpositions might be conscious is equally strange. And the other theories are no less peculiar: Panpsychists believe consciousness may be a fundamental building block of the universe, while other philosophers argue that it is an illusion and does not really exist at all. All these ideas are part of current academic debate.

The Stakes Are High

The sheer strangeness of every theory of consciousness inspired philosopher Eric Schwitzgebel to call his latest book The Weirdness of the World. Rather than simply defending his preferred theory, he surveys the entire landscape of consciousness research and reaches a sober conclusion: “Something that seems almost too strange to believe must be the case.” But we are in no position, he argues, to determine which of these strange theories is correct.

Schwitzgebel’s conclusion might tempt us to bury our heads in the sand and retreat into the comfort of ignorance. But too much is at stake. Consciousness plays a central role in determining a being’s moral status. The main reason we can kick soccer balls but not cats is that cats have conscious experiences and soccer balls do not.

Our ignorance should therefore push us to think harder, not stop. One approach is to ask which kind of error would have more serious consequences. If we wrongly deny consciousness to conscious beings, we could cause tremendous suffering. If we wrongly attribute consciousness to beings that lack it, we would merely treat them better than necessary.

This asymmetry suggests that we should not hastily relegate uncertain cases, such as insects or crustaceans, to the same category as soccer balls. It also shows why consciousness research matters—quite apart from the aura of mystery and strangeness it lends the world.