Quantum mechanics has never been short of mysteries. From superposition and entanglement to the measurement problem, it has repeatedly challenged our familiar assumptions about the physical world.
It was perhaps inevitable that some of these mysteries would attract the attention of researchers interested in another phenomenon that remains incompletely understood: consciousness.
The relationship between quantum physics and consciousness is not new. Indeed, it reaches back to the early debates about measurement, when physicists struggled to understand what happens when a quantum system is observed.
If measurement involves a transition from multiple possible outcomes to a definite result, what role does the observer play? And if the observer is a conscious being, might consciousness itself have some special relationship with the physical processes described by quantum mechanics?
These questions have generated a considerable variety of proposals. Some have become serious subjects of scientific and philosophical investigation. Others have travelled considerably further than their evidence permits.
To understand the difference, we need to distinguish between asking whether quantum processes might contribute to consciousness and claiming that quantum mechanics explains phenomena such as telepathy, psychic communication or survival after death.
They are not the same proposition.
The possibility that quantum physics might contribute to an explanation of consciousness is not equivalent to the claim that consciousness possesses extraordinary quantum powers.
One of the better-known attempts to establish a connection between quantum mechanics and consciousness is the theory developed by physicist Roger Penrose and anæsthesiologist Stuart Hameroff.
Their proposal, known as orchestrated objective reduction, or Orch OR, suggests that quantum processes occurring within structures called microtubules in neurons contribute to conscious experience.
Microtubules are components of the cellular cytoskeleton. They help maintain cellular structure and participate in intracellular transport and other biological processes.
Penrose had independently proposed that consciousness might involve a physical process associated with the reduction of quantum superpositions. Hameroff suggested that microtubules might provide a biological setting for such processes.
Their combined proposal attempts to connect quantum physics, biological organisation and consciousness within a single explanatory framework.
It is an ambitious hypothesis, and it has attracted substantial criticism.
One difficulty concerns the ability of delicate quantum states to persist in the warm, wet and complex environment of the brain. Environmental interactions tend to produce decoherence, potentially destroying the quantum coherence required by the proposal before it could perform the suggested biological role.
The precise biological and physical mechanisms proposed by Orch OR remain disputed, and the theory has not been established as an explanation of consciousness.
Nevertheless, it illustrates an important distinction. A hypothesis proposing that quantum processes contribute to the operation of a biological system is at least a question that can be investigated through physics and biology.
It does not follow that quantum entanglement can explain every mysterious feature of conscious experience.
Unfortunately, the distinction becomes considerably less clear when we move beyond proposals about the physical basis of consciousness itself.
Consider the idea of telepathy.
In popular accounts, quantum entanglement is sometimes invoked to explain how two people might communicate information without any ordinary sensory or physical connection. The reasoning often begins with a genuine feature of quantum physics: entangled systems can exhibit correlations that cannot be explained through ordinary local hidden-variable models.
But the conclusion does not follow.
Entanglement does not provide a means of transmitting controllable information between distant particles. The individual measurement outcomes remain unpredictable, and the correlations become apparent only when the results are compared.
There is no established physical mechanism through which entanglement could provide a telepathic communication channel between human brains.
The fact that two quantum systems can be entangled does not mean that two people who share an emotional or biological relationship become quantum-entangled in the relevant physical sense.
A relationship between a mother and child, for example, can involve extraordinarily complex biological, psychological and social processes. It does not follow that these processes constitute quantum entanglement, or that entanglement explains any intuitive awareness they may experience.
This brings us to another curious development.
Some researchers have attempted to connect quantum entanglement with the relationship between a pregnant mother and her unborn child, proposing that a quantum connection might persist even after physical separation and provide a form of nonlocal intuition.
The suggestion is intriguing at first glance. The mother and child are biologically connected, and the developing organism depends upon an extraordinary network of interactions.
But biological interdependence is not evidence of quantum entanglement. Nor does the existence of quantum processes within biological systems establish a mechanism for transmitting information through entanglement across arbitrary distances.
The proposed explanation requires evidence for each of these steps. The vocabulary of quantum physics cannot substitute for that evidence.
Similar problems arise in claims about meditation.
Some experiments have investigated whether collective meditation events produce correlations in the outputs of quantum random number generators. The suggestion is that human consciousness might somehow influence the behaviour of quantum systems, or that geographically separated generators might become correlated through the collective mental activity of participants.
Such claims require particularly careful examination.
Quantum random number generators are physical devices whose outputs are intended to exploit quantum processes to produce unpredictable results. Their statistical behaviour can be investigated, and experiments can test whether their outputs depart from what would be expected under specified conditions.
But a statistical departure is not, by itself, evidence that meditation has influenced a quantum system.
The experimental design, the statistical analysis, the treatment of multiple comparisons and the possibility of systematic errors all matter. A small probability value cannot rescue an experiment whose assumptions or analysis are defective.
And even if an experiment established a genuine correlation, that would still leave open the question of what physical mechanism produced it.
This is a recurring problem in the appropriation of quantum physics.
A genuine scientific phenomenon is identified. An association is proposed between that phenomenon and something not adequately explained. The association is then treated as though it establishes a physical connection.
But an analogy is not a mechanism, and a correlation is not an explanation.
There is an additional difficulty when we consider claims about consciousness surviving death.
The measurement problem in quantum mechanics has sometimes been interpreted as evidence that consciousness occupies a special position in the physical universe. If consciousness somehow participates in the production of definite measurement outcomes, might it also possess a physical existence independent of the brain?
Could quantum information survive the death of the organism? Could entanglement provide a means through which consciousness persists?
These are extraordinary questions, but the suggested answers require considerably more than an appeal to quantum mechanics.
Quantum information is not synonymous with personal identity, memory or conscious experience. The fact that physical information is subject to conservation principles in particular quantum processes does not establish that an individual's consciousness continues after the biological processes supporting it have ceased.
Nor does quantum entanglement provide evidence for an afterlife.
We should distinguish here between an absence of scientific explanation and positive evidence for a proposed explanation. The fact that consciousness remains incompletely understood does not make every suggested account equally plausible.
And this is where we think our exploration becomes particularly interesting.
The problem is not that people are fascinated by quantum physics, nor that they are interested in consciousness. Both subjects deserve sustained investigation. Nor should we dismiss a hypothesis merely because it challenges familiar assumptions.
The problem arises when the strangeness of one phenomenon is used to establish the existence of another.
Quantum entanglement is genuinely remarkable. Consciousness is genuinely remarkable. But the fact that both challenge familiar explanatory assumptions does not establish that one explains the other.
We have spent four instalments examining what entanglement actually involves. We have encountered shared quantum states, nonlocal correlations, the limitations of separable descriptions and the physical relationships involved in measurement.
None of these requires telepathy, psychic communication or the survival of consciousness after death.
Indeed, the actual physics is sufficiently interesting without adding claims that it cannot support.
Perhaps this is the most useful distinction we can draw from the present exploration.
An unexplained phenomenon can provide a reason to investigate. It cannot, by itself, provide evidence for whatever explanation we happen to find attractive.
The mysteries of consciousness remain. The foundations of quantum mechanics remain subjects of investigation. There may yet be important discoveries concerning their relationship.
But those discoveries will have to emerge from evidence, experimental investigation and explanations that can withstand scrutiny.
The world does not become more mysterious simply because we attach the word quantum to something we do not understand.
Sometimes, the mystery is already extraordinary enough.
And that leaves us with a rather different question.
How do scientific ideas acquire the authority to explain phenomena far beyond the circumstances in which they were originally developed? How does a legitimate scientific concept become an apparently universal explanatory resource?
Perhaps the most interesting relationship we have yet to examine is not between entangled particles and consciousness, but between scientific knowledge and the ways in which people use it.
That is where we shall turn next.
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