In 1935 Einstein, Podolsky and Rosen published a paper now known as the EPR paradox. Formally, the authors wanted to show that quantum mechanics is incomplete; in practice, they gave the first description of what would later be called quantum entanglement.
Einstein called it spooky action at a distance. He was convinced it was an artefact and that a deeper local theory with hidden variables stood behind quantum mechanics.
In 2015 Ronald Hanson's group at Delft University of Technology ran a loophole-free Bell test: electron spins in diamond defects 1.3 kilometres apart, with neither the locality loophole nor the detection loophole left open. The result: Bell's inequality is violated, and local realism is dead.
This measurement is no longer up for dispute. The same year, similar results came from Zeilinger's group in Vienna and from NIST in the United States, and later from Munich, all telling the same story.
What this does not imply
Quantum nonlocality does not get you to a brain that is a quantum computer, to consciousness smeared across the universe by entanglement, or to a mind you can "upload" to the cloud and "tune" to a field.
The usual interpretive mistake is to take a real physical fact (entanglement exists) and bolt a speculation onto it (entanglement operates in the brain), as if the first supported the second. It does not.
What this may imply
Since the mid-1990s Roger Penrose and Stuart Hameroff have been developing the Orch-OR hypothesis: coherent quantum states exist in neuronal microtubules, and their collapse is tied to moments of conscious choice. Most physicists were sceptical, since at body temperature decoherence should destroy any coherence almost instantly.
Recent years have given the hypothesis some support. In 2023 Gregory Scholes's group at Princeton showed that excitation energy travels along microtubules farther than classical models predict (ACS Central Science). In 2024 Philip Kurian's group at Howard University found superradiance in tryptophan networks inside microtubules, a collective quantum effect that persists at room temperature (Journal of Physical Chemistry B). This is a long way from proving Orch-OR, but the hypothesis can no longer be dismissed out of hand.
It is an interesting position: a theory that once sat outside serious discussion has moved into testable speculation.
Tononi and integrated information theory
Giulio Tononi proposed a different approach, integrated information theory (IIT). Consciousness, for Tononi, is a measure of how integrated a system is, written Φ (phi). The more a system behaves as a single whole and the less as a set of independent parts, the higher its Φ.
The theory is elegant. Its main weakness is computational: the exact Φ of a system the size of a brain cannot be computed, because the complexity grows exponentially. Critics led by Scott Aaronson point to something else as well: IIT makes strange predictions for artificial systems, for instance assigning a simple grid of logic gates more consciousness than a human. Tononi acknowledges the problem but keeps the theory.
For an honest theory this is a normal position: it makes predictions that can be criticised.
What I think
I sort my conclusions into three levels of confidence.
Established: quantum mechanics is nonlocal (Delft, 2015, and later experiments); information is physical (Landauer, 1961; experiment, 2012); consciousness depends on how integrated brain activity is, and the number of neurons alone decides nothing: the cerebellum holds most of them yet contributes almost nothing to consciousness.
Preliminary: microtubules may sustain quantum effects longer than previously thought. Orch-OR has become a subject of discussion, though it remains unproven.
Speculation: if gravity is emergent (Verlinde), the universe is a neural network (Vanchurin) and consciousness is integrated information (Tononi), then all three claims may describe one phenomenon from different sides. That is speculation, of course, but speculation you can start testing.
Quantum consciousness today is a set of measurements, each of which is still alive, with no finished theory underneath them yet.