Could consciousness be a quantum phenomenon? Nobel physicist Roger Penrose proposes quantum processes in brain microtubules create awareness. The theory is controversial, untestable, and compelling all at once.
Biswarup Ganguly, CC BY 3.0, via Wikimedia Commons
The quantum soul machine
At the core of your neurons are tiny, hollow cylinders called microtubules. Traditionally, their job is structural support and transport, like a cellular skeleton. But in the early 1990s, Nobel laureate physicist Sir Roger Penrose and anesthesiologist Stuart Hameroff proposed a far more exotic function for them. Their theory, known as Orchestrated Objective Reduction (Orch OR), suggests that these microtubules are the site of quantum computations that generate conscious experience.
The idea starts with Penrose's work on the foundations of physics and mathematics. He argued that human understanding shows non-algorithmic properties, which classical computers can't replicate, and turned to quantum mechanics for an answer. Hameroff, meanwhile, was studying microtubules and wondered how anesthetic gases could selectively switch off consciousness. He proposed that anesthetics work by dampening quantum vibrations in these specific structures. They teamed up in 1992, suggesting microtubules could host and protect delicate quantum states from the brain's noisy classical environment. Each microtubule is a polymer made of a protein called tubulin, which could act as a quantum bit, or qubit, capable of existing in a superposition of multiple states at once.
An orchestrated collapse
The "Orchestrated" part of the theory refers to the idea that synaptic inputs and proteins attached to the microtubules help "tune" these quantum computations. The "Objective Reduction" is Penrose's own controversial solution to the quantum measurement problem. He posits that quantum superposition isn't just a state of uncertainty waiting for an observer; it's a real physical state that has its own instability. When a superposition reaches a specific gravitational threshold, it collapses into a definite state on its own.
According to Orch OR, this physical collapse is a moment of "proto-consciousness." A sequence of these events, occurring at frequencies potentially related to gamma brain waves (30-90 Hz), creates our stream of conscious awareness. The theory challenges the mainstream neuroscience view that consciousness is an emergent property of complex classical computations among neurons.
The hypothesis faces major criticism. The principal objection is decoherence; physicists argue the brain is far too "warm and noisy" to sustain quantum coherence for any meaningful length of time. Calculations by physicist Max Tegmark in 2000 suggested that any quantum coherence in microtubules would be destroyed by the surrounding environment in femtoseconds, far too quickly to influence neural processes. Despite the critiques, research continues at the University of Arizona's Center for Consciousness Studies, co-founded by Hameroff, which hosts the biennial "The Science of Consciousness" conference, a major gathering for researchers in the field since 1994.
💡Fun Facts
Stuart Hameroff is a practicing anesthesiologist, and his hypothesis stems from questioning how different inert gases can universally switch off consciousness while leaving non-conscious brain functions intact.
Roger Penrose was partly inspired by Gödel's incompleteness theorems, which imply that human consciousness can grasp mathematical truths that are unprovable by any formal system.
The theory suggests consciousness is fundamental to the universe rather than a product of biology, with each "objective reduction" being a selection of information embedded in the basic geometry of spacetime.
Microtubules are not unique to neurons; they exist in almost all plant and animal cells, which poses the question of what makes brain microtubules special for consciousness.
The University of Arizona campus is generally open to the public. The Center for Consciousness Studies does not have public visiting hours, but hosts regular conferences and events.
Admission
Free to visit the campus. Conference and event attendance requires registration and fees.
Accessibility
The University of Arizona campus is largely flat and wheelchair accessible.
