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A key question that the science of psychedelics has not even begun to answer is whether the new neural connections that psychedelics make possible endure in any way, or if the brain’s wiring returns to the status quo ante once the drug wears off. The finding by Roland Griffiths’s lab that the psychedelic experience leads to long-term changes in the personality trait of openness raises the possibility that some kind of learning takes place while the brain is rewired and that it might in some way persist. Learning entails the establishment of new neural circuits; these get stronger the more exercise they get. The long-term fate of the novel connections formed during the psychedelic experience—whether they prove durable or evanescent—might depend on whether we recall and, in effect, exercise them after the experience ends. (This could be as simple as recollecting what we experienced, reinforcing it during the integration process, or using meditation to reenact the altered state of consciousness.) Franz Vollenweider has suggested that the psychedelic experience may facilitate “neuroplasticity”: it opens a window in which patterns of thought and behavior become more plastic and so easier to change. His model sounds like a chemically mediated form of cognitive behavioral therapy. But so far this is all highly speculative; as yet there has been little mapping of the brain before and after psychedelics to determine what, if anything, the experience changes in a lasting way.

Carhart-Harris argues in the entropy paper that even a temporary rewiring of the brain is potentially valuable, especially for people suffering from disorders characterized by mental rigidity. A high-dose psychedelic experience has the power to “shake the snow globe,” he says, disrupting unhealthy patterns of thought and creating a space of flexibility—entropy—in which more salubrious patterns and narratives have an opportunity to coalesce as the snow slowly resettles.

• • • THE IDEA that increasing the amount of entropy in the human brain might actually be good for us is surely counterintuitive. Most of us bring a negative connotation to the term: entropy suggests the gradual deterioration of a hard-won order, the disintegration of a system over time. Certainly getting older feels like an entropic process—a gradual running down and disordering of the mind and body. But maybe that’s the wrong way to think about it. Robin Carhart-Harris’s paper got me wondering if, at least for the mind, aging is really a process of declining entropy, the fading over time of what we should regard as a positive attribute of mental life.

Certainly by middle age, the sway of habitual thinking over the operations of the mind is nearly absolute. By now, I can count on past experience to propose quick and usually serviceable answers to just about any question reality poses, whether it’s about how to soothe a child or mollify a spouse, repair a sentence, accept a compliment, answer the next question, or make sense of whatever’s happening in the world. With experience and time, it gets easier to cut to the chase and leap to conclusions—clichés that imply a kind of agility but that in fact may signify precisely the opposite: a petrifaction of thought. Think of it as predictive coding on the scale of life; the priors—and by now I’ve got millions of them—usually have my back, can be relied on to give me a decent enough answer, even if it isn’t a particularly fresh or imaginative one. A flattering term for this regime of good enough predictions is “wisdom.”

Reading Robin’s paper helped me better understand what I was looking for when I decided to explore psychedelics: to give my own snow globe a vigorous shaking, see if I could renovate my everyday mental life by introducing a greater measure of entropy, and uncertainty, into it. Getting older might render the world more predictable (in every sense), yet it also lightens the burden of responsibility, creating a new space for experiment. Mine had been to see if it wasn’t too late to skip out of some of the deeper grooves of habit that the been-theres and done-thats of long experience had inscribed on my mind.

• • • IN BOTH PHYSICS and information theory, entropy is often associated with expansion—as in the expansion of a gas when it is heated or freed from the constraints of a container. As the gas’s molecules diffuse in space, it becomes harder to predict the location of any given one; the uncertainty of the system thus increases. In a throwaway line at the end of his entropy paper, Carhart-Harris reminds us that in the 1960s the psychedelic experience was usually described as “consciousness-expansion”; knowingly or not, Timothy Leary and his colleagues had hit on exactly the right metaphor for the entropic brain. This expansion metaphor also chimes with Huxley’s reducing valve, implying as it does that consciousness exists in a state of opening or contraction.

As a matter of experience, a quality as abstract as entropy is almost impossible for us to perceive, but expansion, perhaps, is not. Judson Brewer, the neuroscientist who studies meditation, has found that a felt sense of expansion in consciousness correlates with a drop in activity in one particular node of the default mode network—the posterior cingulate cortex (PCC), which is associated with self-referential processing. One of the most interesting things about a psychedelic experience is that it sharpens one’s sensitivity to one’s own mental states, especially in the days immediately following. The usual seamlessness of consciousness is disturbed in such a way as to make any given state—mind wandering, focused attention, rumination—both more salient and somewhat easier to manipulate. In the wake of my psychedelic experiences (and, perhaps, in the wake of interviewing Judson Brewer), I found that when I put my mind to it, I could locate my own state of consciousness on a spectrum ranging from contraction to expansion.

When, for example, I’m feeling especially generous or grateful, open to feelings and people and nature, I register a sense of expansion. This feeling is often accompanied by a diminution of ego, as well as a falloff in the attention paid to past and future on which the ego feasts. (And depends.) By the same token, there is a pronounced sense of contraction when I’m obsessing about things or feeling fearful, defensive, rushed, worried, and regretful. (These last two feelings don’t exist without time travel.) At such times, I feel altogether more me, and not in a good way. If the neuroscientists are right, what I’m observing in my mind has a physical correlate in the brain: the default mode network is either online or off; entropy is either high or low. What exactly to do with this information I’m not yet sure.

• • • BY NOW, it may be lost to memory, but all of us, even the psychedelically naive, have had direct personal experience of an entropic brain and the novel type of consciousness it sponsors—as a young child. Baby consciousness is so different from adult consciousness as to constitute a mental country of its own, one from which we are expelled sometime early in adolescence. Is there a way back in? The closest we can come to visiting that foreign land as adults may be during the psychedelic journey. This at least is the startling hypothesis of Alison Gopnik, a developmental psychologist and philosopher who happens to be a colleague of mine at Berkeley.

Alison Gopnik and Robin Carhart-Harris come at the problem of consciousness from what seem like completely different directions and disciplines, but soon after they learned of each other’s work (I had e-mailed a PDF of Robin’s entropy paper to Alison and told him about her superb book, The Philosophical Baby), they struck up a conversation that has proven to be remarkably illuminating, at least for me. In April 2016, their conversation wound up on a stage at a conference on consciousness in Tucson, Arizona, where the two met for the first time and shared a panel.