Neuroscience can map every function of the brain and still not explain why there is something it is like to be one. The gap between mechanism and experience, named by David Chalmers, refuses to close.
Documented
The naming and the frame
Documented: Chalmers, Facing Up to the Problem of Consciousness (1995), separated the easy problems, functions explicable in principle by cognitive science, from the hard one, subjective experience itself. The ancestry is older: Nagel's What Is It Like to Be a Bat? (1974) made the point with wings, and Levine's explanatory gap (1983) gave it its first technical name. The problem's status today: no accepted solution, and no agreement on what a solution would even look like.
Assessment: Documented as the central open problem of consciousness science. Unlike most entries here, the mystery is not contested by cranks at the edges; it is announced from the center of the field.
Stories
The ghost that survived the machine
The folk version is everyone who has ever felt their own thinking and doubted a scanner could hold it: the soul by another name, the inner light the instruments keep missing. It powers a thousand dorm-room arguments and one very durable intuition, that I know I am conscious more certainly than I know anything else.
Assessment: Documented as near-universal intuition, which is precisely what the researchers argue about. Illusionists like Dennett and Frankish reply that the intuition is the thing to be explained away; the folk tier is not the solution, it is the evidence under dispute.
Interesting claims
The bridges being built anyway
The interesting claims are the proposed crossings: Integrated Information Theory makes consciousness identical to a mathematical quantity, Phi, and grants it to anything sufficiently integrated, thermostats included; Orchestrated Objective Reduction places it in quantum events inside neural microtubules, extending it backward before life; panpsychism simply installs it as a base property of matter. Each solves the problem by redefining where consciousness lives.
Assessment: All documented, all seriously argued, none confirmed. The field's honest summary: three decades of ingenious answers to a question we cannot yet check. The hard problem remains the best-labeled hole in modern science.
Sources and further reading
Chalmers, Facing Up to the Problem of Consciousness (1995), the naming
Nagel, What Is It Like to Be a Bat? (1974)
Levine, Materialism and Qualia: The Explanatory Gap (1983)
Dennett and the illusionist replies; Frankish, Illusionism as a Theory of Consciousness (2016)
Tononi, Integrated Information Theory; Hameroff and Penrose, Orchestrated Objective Reduction, the bridging claims
Worth asking
If no instrument can detect your inner life, is it the universe's biggest phenomenon or its most persistent misunderstanding?