In April 1994, a young, mulleted Australian philosopher named David Chalmers delivered a lecture at the University of Arizona and articulated what’s now known as the “hard problem” of consciousness. Namely, how is it that unfeeling biological processes can give rise to the feeling of a unified, conscious self? How does the mind, in other words, arise from matter?

The following year and thousands of miles away, a 14-year-old Brit named Robin Carhart-Harris was doing a little consciousness research of his own: he and a couple friends had just taken LSD for the first time. It was the nadir of the psychedelic dark ages, over two decades since the passing of the Misuse of Drugs Act, which provided the legal basis for the regulation of drugs across the UK; psychedelics were listed as Class A, Schedule I substances — the Act’s most tightly controlled category. For the young Carhart-Harris, that first LSD experience would prove fateful: It “gave me the initial sense of wonder, and it did determine the path that I took,” he told me recently over a Zoom call. Looking back, that path would turn out to be as implausible as the wall-melting visuals of an acid trip.

Today, Carhart-Harris is the Ralph Metzner Distinguished Professor in Neurology and Psychiatry at the University of California, San Francisco, a position he’s held since 2021. He’s in his 40s, with sharp features, a crop of silvering dark hair, and glacier-blue eyes that seem as fixated and alert as an owl’s. He speaks with the measured cadences — sometimes almost in a whisper — of one used to defending controversial ideas. But he’s by no means reserved. The first time we spoke back in January, I was immediately disarmed by his openness and soft-spoken exuberance: Here was someone who clearly loves what he does for a living.

Within the small but ever-growing field of contemporary psychedelic science, he’s become something of a Carl Sagan-like figure: a straitlaced and prolific researcher who also happens to have a gift for communicating abstract scientific ideas to a popular audience. (He’s probably the only neuroscientist to have appeared as a guest on Gen Z influencer Emma Chamberlain’s podcast, for example, and this past weekend, he appeared in longevity influencer Bryan Johnson’s livestreamed 5-MeO-DMT experience; he’s also working on a forthcoming book about psychedelics.) But more importantly, he’ll be remembered as one of the very few pioneering researchers who, in the earliest years of this century, had the audacity to reignite the spark of psychedelic research that had been almost completely snuffed out a decade before his birth.

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Carhart-Harris’ first psychedelic foray cracked open a mental door through which he was able to catch a brief, dazzling glimpse of uncharted coastlines in the geography of his own mind. Plenty of psychonauts before him had explored that psychological terra incognita. But for Carhart-Harris, exploring and reporting those experiences after the fact wasn’t enough — not if we hoped to truly understand the mind. For that, we would need maps. 

At first, the surest path to achieving that goal seemed to him to be psychoanalysis, the subfield of psychology founded at the end of the 19th century by Sigmund Freud. Freud likened the human psyche to an iceberg, with only a small tip poking into conscious awareness and the vast majority — the unconscious — lurking unseen in the depths. The ego, or our sense of being a unified self, is, according to Freud, actually composed and at the whim of a throng of subpersonalities, each pursuing its own agenda and vying for dominance over the others. He believed dreams were a kind of gateway through which the cryptic murmurings of the unconscious could be heard, and even deciphered.

Carhart-Harris started a master’s program in psychoanalysis at Brunel University of London, but his interest soon waned. A budding naturalist, dream analysis seemed to him to be a maddeningly squishy route into the unconscious mind. (It was a master of arts program, he told me pointedly.) “I felt like in my character, even at that young age, that I wanted more rigor,” he says. “I was frustrated by the looseness of it.” The “royal road” to the unconscious, as Freud had famously described dreams, seemed to the young Carhart-Harris to be more of a labyrinth. He remembered his first LSD trip back in ‘95, that feeling he’d had of fleetingly gazing upon previously unknown psychological terrain, and wondered: Was it possible that a drug could be a more direct and fruitful pathway to the unconscious than dreams?

And so one day he perched himself in front of a computer and searched for anything containing the words “psychedelics” and “unconscious.” Up popped a link to Realms of the Human Unconscious, a book published in 1975 by the Czech psychiatrist Stanislav Grof. Written during the Soviet occupation of Czechoslovakia, Realms recounts Grof’s experiments dosing hundreds of people with LSD, including fellow psychiatrists and people with mental health disorders, at the Psychiatric Research Institute in Prague and later at Spring Grove State Hospital in Maryland. Grof was deeply impressed by what he came to regard as the genuine therapeutic potential of psychedelics, famously comparing their utility for the field of psychology to the telescope’s for astronomy and to the microscope’s for biology. Carhart-Harris was captivated: Here, finally, was an approach to studying the unconscious that gelled with his own intuitions (and experience), one which seemed to bridge the gap between psychoanalytic theory and hard science. “This changed everything,” he recalls.

Grof’s later work — much of it elaborating upon his theory of birth trauma — waded into some intellectual territory that was too far out for Carhart-Harris’ tastes. But Realms showed him that he didn’t have to embark on the venture of mapping the unconscious completely blind: there were others who had begun sketching out the topography before him, aided by the illuminative power of psychedelics.

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If Grof confirmed for Carhart-Harris that those far-flung mental shores were real, it was David Nutt who helped him build a ship to reach them.

Nutt is a neuropsychopharmacologist — a scientist studying the effects of drugs on the brain — with a flair for going against the establishment grain. In 2009, he was fired from his position as chair of the UK government’s Advisory Council on the Misuse of Drugs for arguing in a paper that the country’s existing laws were dangerously divorced from the actual science of drugs and their respective risks and benefits. (He’s also famously claimed that taking ecstasy is less risky than horse riding.) When Carhart-Harris first met him, in 2005, he was a professor in his 50s at the University of Bristol. Carhart-Harris found in Nutt a reputable researcher unafraid of a little notoriety; Nutt, in turn, found a bold and energetic protegé. 

With Nutt as his adviser, Carhart-Harris completed a Ph.D. in the psychopharmacology of the brain’s serotonin system — the same system which the so-called “classic” psychedelics, including LSD and psilocybin, act upon. Then in 2009, with funding from Amanda Fielding, the late Countess of Wemyss and March and founder of the Beckley Foundation, Carhart-Harris embarked on a study observing brain activity under the influence of psilocybin. Neuroimaging technologies like functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), coupled with psychedelics, he hoped, would together bring the vaguely charted realms of the unconscious mind into the light of empirical science.

And after decades of stigma and prohibition, scientific interest in psychedelics was also on the rise. Just a few years earlier, in 2006, a landmark paper published by researchers from Johns Hopkins University showed that psilocybin in conjunction with psychotherapy can produce profound “mystical-type experiences” which the volunteers in the study later said had been among the most significant events of their entire lives, and had caused a variety of positive behavioral changes — claims that were backed up by the people around them — including shifts in mood, outlook, and social behavior. Still, the burgeoning field was shaky, at best. “[If] we overdose a participant or send him psychotic, this is dead,” Carhart-Harris remembers thinking before he embarked on his first study with psychedelics. “One serious adverse event, and [psychedelic research] is firmly back in deep freeze.” 

He recalls Nutt putting things to him more bluntly: “Don’t fuck this up.”

Thankfully for the nascent psychedelic renaissance, he didn’t. For the study — published in 2012 in the Proceedings of the National Academy of Sciences — a group of 15 healthy adults were given psilocybin or a placebo before being placed in a fMRI scanner, a machine that looks like a giant cylindrical eyeball; the subjects are lain onto a flat surface and then slid down the middle of the machine, into the scanner’s iris. Each full scanning session lasted a little under an hour. Being stuck inside of a narrow metal tunnel with a cacophony of machinery pounding around your head doesn’t seem like the ideal setting for a psychedelic experience, yet the study proceeded smoothly, without a single serious adverse event. Afterwards, both groups were asked to rate the intensity of their experiences based on a number of descriptive criteria, including “Things looked strange” and “My sense of time was altered.” Unsurprisingly, the psilocybin group’s ratings dwarfed those of their sober counterparts across the board.

What was surprising were the brain scans of the psilocybin group. Going into the study, Carhart-Harris and his colleagues had assumed that the quantifiable data gleaned from a tripping brain would somehow resemble the quality of the experience itself: a kaleidoscopic profusion of activity. Instead, they found that the brain under the influence of psilocybin was, as it were, quieting down. fMRI measures changes in blood oxygen levels across different areas of the brain to determine, in effect, how those regions are talking to one another. The more closely synchronized the changes in two particular areas are, the greater the functional relationship between them (hence the “f” in “fMRI). In the psilocybin group, blood oxygenation levels in “hub” regions — the neural equivalent of major international airports — like the thalamus and the anterior/posterior cingulate cortices were reduced. And the steeper the drop-off, the higher the volunteers rated the intensity of their trips. The temporary decrease in mental chatter occasioned by psilocybin, Carhart-Harris and his coauthors concluded in the paper, gives rise to “an unconstrained style of cognition.”

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Two years later, in 2014, Carhart-Harris published another paper outlining his theory of what he called “the entropic brain.” Drawing upon the findings from the fMRI study with psilocybin, he argued that psychedelics induce a state of “primary consciousness” akin to that experienced by very young children and perhaps also by human beings’ evolutionary ancestors. The idea is that modern adult brains have evolved to maintain a delicate internal balance between entropy, or randomness, and order. 

We need to be able to explore our environment and forage for information (hence the “entropic” brain state), but since we outsource so much of our cognition to the people around us and to society at large, it’s also useful for us to fall into more or less healthy routines once we’ve learned the general rules of the culture we’re born into (that would be the orderly part coming online).

But as many of us can readily attest, that equilibrium is a delicate one. The brain can veer into an excessively disordered state, resulting, for example, in psychosis. On the other hand, it can become too rigid, locking us in counterproductive patterns of thought and/or behavior — as in the case of depression, say. (That word is illustrative, according to Carhart-Harris: “I’ve always thought that there’s something intuitive about the term itself, like a depression in a landscape…that’s easy to fall into, and if you do it’s hard to get out of,” he said during a 2023 appearance on the neuroscientist Andrew Huberman’s podcast.) In the overly-orderly brain of someone living with chronic depression, OCD, or PTSD — all of which involve ruminative patterns of thought — the ego becomes less of a protective shell for navigating the complexities of the social world and more of a prison trapping us inside ourselves, and often as a result, closing us off from social connection.

What psychedelics have the potential to do, Carhart-Harris proposed, is temporarily loosen the grip of the brain’s key connector hubs — particularly that of the default mode network, which comes online during self-referential thought (social anxiety, worrying about future obligations, and so on) — and induce a high-entropy brain state. But it’s not the jumbled confusion of psychosis; it’s more like a state of sheer psychic potential, akin to that of a newborn experiencing everything for the first time. Freed from the domineering dictates of the ego, the highly entropic brain is shaken up, snowglobe-like, allowing for the formation of new neuronal connections and habits.

***

That’s the theory, anyway. 

Carhart-Harris led another study, published in 2016 in The Lancet, which found that 12 adults with treatment-resistant depression all reported measurable decreases in their symptoms following two guided psilocybin sessions, seemingly backing up the entropic brain model. A follow-up study published five years later in The New England Journal of Medicine, however, showed that psilocybin’s antidepressant effects weren’t meaningfully higher than those caused by Lexapro, the widely prescribed antidepressant. Carhart-Harris is careful to point out that there were a number of secondary outcomes from that latter study, including the likelihood of remission, that seemed to favor psilocybin, but due to some methodological limitations, the authors had to admit it was possible that those could be attributed purely to chance. But a more recent analysis of clinical trials using psychedelics and antidepressants to treat depression found no statistically significant difference between the two. In short: It seems promising that psilocybin-assisted therapy can help to alleviate depression for some people, but it will take more research to figure out if they’re actually more effective than traditional SSRIs like Lexapro.

Studying the efficacy of the two is obviously important, but Carhart-Harris is also thinking in broader terms: comparing not only two categories of drugs but two radically different medical paradigms: the long-reining, pill-a-day regimen of prescription medicine, and a potentially new model in which one has the option to undergo a psychedelic session with a trained therapist and potentially feel better for months afterward, maybe longer. He says he’s “on the cusp” of gaining approval to proceed with another study testing the efficacy of psilocybin versus Lexapro, this time exclusively with younger adults (ages 18 to 25). “They're at a pivotal point in life, and they could easily go down a track of taking an SSRI every day for many years,” he says. “Is that going to help them really? Is that going to give them a life of deep satisfaction, or will it just help them get by? … maybe they should also understand, and their families should understand, that there could be another treatment that could be more thoroughly restorative — and that would be the psilocybin.”

On a theoretical level, Carhart-Harris’ entropic brain model could also yield new insights into the origins and nature of consciousness. As of early 2026, Chalmers’ infamous hard problem remains as obstinate as ever: there’s still no scientific consensus for how conscious experience can arise from the interplay of billions of neurons, and some experts believe that the scientific method itself, with its orientation around objectively testable hypotheses, is fatally unable to account for purely subjective experiences.

Carhart-Harris makes no claim to have solved the riddle of consciousness. He’s still the cognitive cartographer, devoted to the project of charting the connection between mind and brain. “The best we can achieve is a really good map,” he tells me. “And I think over the next few decades, we're going to get better and better maps.”

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