A Month Left in the Ice

Into the Dark Chasm

Mara: It's 1962, in the French Alps. Michel Siffre, a cave scientist, is going down a vertical pothole, 130 feet of it, into an ice cavern. He'll stay about 63 days. No sunlight. No clock. No calendar. There's a phone line to his team on the surface, but only he uses it: when he wakes, and before he sleeps. They never call down, and they never tell him the time. Everything else goes into the diary he kept down there.

Eli: Which is the listener's question, exactly: is time real, or something our brains make up?

Mara: His setup puts that question in its rawest form. No sun to rise, no clock to glance at, just a man and his own sense of the hours. What he'd signed up for was subterranean isolation, about as literal as it gets. Today's angle is a speleologist's subterranean isolation exposing the split between physical time and neural construction.

Eli: Meaning a man underground with nothing outside telling him the hour.

Mara: Nothing outside, and nobody allowed to slip him a hint. Just his own guesses, in the diary.

Eli: So the setup is clean: one man, one phone, no way to check the time. What it did to his sense of the hours is Mara's part.

The Warping of the Minutes

Mara: By August 30th, 1962, he's deep into it. He writes: "Forty-second awakening. I cannot sleep tonight, so will give myself over to dictating in the darkness my thoughts on time and other things." And the thoughts are unsettling. That morning he'd phoned the surface and talked a while. Afterward he wondered how long the call had lasted, and "could not even hazard a guess." Then this line: "Time does not seem to pass slowly, but on the contrary passes quickly."

Eli: Quickly. For a man alone under the Alps.

Mara: And a test caught it in numbers. He counted from one to 120, one digit a second. It took him five minutes. In his words, "I psychologically experienced five real minutes as though they were two." That's subjective duration distortion: the count in his head and the real clock drifting apart. Siffre had his own explanation. He believed that in total darkness, memory doesn't capture the time. After a day or two, he said, he couldn't recall what he'd done a day or two earlier.

Eli: And it isn't only Siffre. In a 2021 cave isolation study, participants spent 40 days underground. Before they went in, their sleep-wake cycles ran close to a day. Inside, the average stretched to roughly 31 and a half hours. By the time they came out, they'd lived only about 29 of those longer days. Minutes or days, the guesses run wrong. How the brain encodes millisecond timing, researchers still debate.

The Fabricated Clock

Mara: The research on time perception keeps landing here. People don't perceive time directly. What they perceive are events, things happening and changing, and they make sense of time from those. One researcher goes further, arguing that people never perceive the passage of time at all, only how their own brain changes. Now put Siffre back in his cave. Complete darkness, cycle after cycle, and his own hunch that memory stops capturing time in the dark. Very little happening. That's the setting where five minutes came out as two.

Eli: So the five minutes weren't misread off some inner stopwatch.

Mara: Then where in the brain does the counting happen?

Eli: In stages, by one recent account. The timing signal for things people see moves from the visual areas at the back of the brain toward the frontal regions, getting reworked along the way. That's hierarchical cortical processing: an assembly line, each station refining what the last one passed on. The researchers' conclusion was that time perception isn't one single process. It's the outcome of several stages spread across the cortex.

Mara: So the felt minute is a finished product.

Eli: And the product can be bent. In another experiment, people watched a gray circle stay on screen for the same length of time, thirty times over. Brain cells in the parietal cortex tuned to that particular duration got tired. Show someone 450 milliseconds again and again, then switch to 500, and the new circle felt even longer than it was. Every one of those steps is the brain building a duration out of what it's given. None of it says whether there's any time out there for it to build from.

The Spacetime Fabric and the Arrow

Mara: Back to the Alps. September 14th, 1962. His team tells him it's over, time to come up. Siffre doesn't believe it. By his own count it's only August 20th, and he's sure he has another month to go. Down there, 130 feet under with no clock, his mind had lost more than three weeks. But here's what he said about the rest of it: "My sleep was perfect! My body chose by itself when to sleep and when to eat."

Eli: So the man who couldn't count to 120 kept a schedule anyway.

Mara: Without knowing he was doing it. His own line: "Without knowing it, I had created the field of human chronobiology." That's the study of the timekeeping bodies do on their own, the internal rhythms that run sleep and hunger with no clock to check. So the cave answered the question it was set up to ask. Take away every clock and the sun, and something in him still kept time. It just wasn't the part of him doing the guessing.

Eli: Though a body keeping time still doesn't say what time is. Physics has its own account, and it's stranger. Relativity has no master now. Two observers moving fast relative to each other can disagree about the order of two distant flashes, as long as they're too far apart for one to cause the other. Causes still come before effects. But there's no shared present. Carlo Rovelli and a co-author put it flatly: relativity "does not permit an objective notion of a global present."

Mara: So "now" is local. Every observer carries their own.

Eli: Which is why many physicists, Rovelli among them, describe a block universe. Think of every frame of a film laid out on a table at once. Past, present and future events all exist in one four-dimensional spacetime, ordered earlier and later, and those relations never change. Nothing flows. The one direction physics does find comes from entropy, roughly the universe's steady unwinding toward equilibrium. Ice cubes melt in a glass. Balls roll downhill. Never the reverse. And that frozen block sits behind one of the most quoted lines about time. In March 1955, Albert Einstein wrote about this.

Mara: In one translation, he wrote: "For people like us who believe in physics, the separation between past, present and future has only the importance of an admittedly tenacious illusion."

Eli: A condolence, written in the physics of no global now.

Mara: So that's the sharper problem. A body keeps its rhythm and relativity keeps its intervals, but whether time sits at the very bottom of nature is a separate fight. Eli has the physicists who say it doesn't.

Timeless Equations vs. Real Becoming

Eli: Start in 1967. Two physicists, trying to fold relativity's spacetime into a quantum description of the whole universe, wrote down what's now called the Wheeler-DeWitt equation. Think of it as one equation for the entire cosmos. And time doesn't appear in it. Not slowed, not relative. Gone. Physicists like Carlo Rovelli read results like that as a sign time isn't fundamental. His view is that time shouldn't appear in a quantum theory of gravity at all, and quantum-gravity programs often claim it emerges from timeless physics underneath.

Mara: Then the equations took away time.

Eli: On that reading, time only shows up at large scales.

Mara: Eli, the other camp reads the same physics and comes out somewhere else. Lee Smolin is one of the physicists who hold that time is fundamental, woven into the universe. He's built a version of presentism, the view that only the present exists: the past is over, the future not there yet. In his words, "The future is not now real and there can be no definite facts of the matter about the future." For him, time is the process that generates future events out of present ones.

Eli: So Einstein's tenacious illusion lands squarely in the first camp.

Mara: Not on this side. George Ellis pictures the present as the place where the indefinite future turns into the definite past. Not a fixed block, then. A present that's doing work.

Eli: Same relativity, same equations, two readings. Whether time is the floor of reality or something built on top of it is still argued between them.

The Limits of the Mind's Clock

Mara: Ten years after the Alps, in 1972, Siffre went down again, into a cave in Texas. This time his body did something stranger. Twice, his day stretched to about 48 hours. He'd be awake for 36 hours straight. Then he'd sleep for 12. That's circadian desynchronization: the body's daily cycle coming loose from the planet's day and night. In later experiments with other people, he said, 48-hour cycles became common. And when he went back through his cave diary, cycle by cycle, he found no sign he'd felt those long days any differently from normal ones.

Eli: A double-length day, and the man who said darkness erases memory never noticed.

Mara: And he's blunt about what that means. "I have no theory. I don't make theories. The forty-eight-hour cycle is a fact." Nobody, he said, understands what could cause such a big split in the sleep-wake cycle. What he was sure of was the larger finding, the one that began in the Alps when his body chose its own hours: the experiments proved an internal clock, independent of the natural day and night. Then he put the question back on the table himself. "What is time? We don't know."

Eli: Part of the trouble is that the listener's question is really two, in one framing that people still argue over. Are physical events related in time in ways that can be measured? Or does the felt flow from past to future exist without minds? Physics answers the first with clocks. It compares durations, orders events by cause and predicts how measurements change, and those intervals have measurable consequences. For the second, the brain has been described as an imperfect clock, chunking physical time into experienced intervals, because neural processes take time.

Mara: Which is Siffre at the bottom of that 130-foot pothole, living both halves. His findings point one way: his body held its own physical rhythm, while his conscious sense of duration was built, and built imperfectly. Five minutes felt like two.

Eli: So, plainly. Time is real the way physics measures it: intervals between events, an order of causes, entropy running one way. The feeling of a present that flows is something the brain builds. That doesn't make the feeling fake. Consciousness is real, and the felt passage of time is a key part of it, whether or not it matches physical time.

Mara: So the signals to watch are specific. Whether cosmology can say why the early universe began with such low entropy, setting the arrow going. Whether physics can square equations that run either way with an arrow that only runs one. Whether loop quantum gravity, which weaves space from tiny loops, or entanglement experiments show time emerging rather than fundamental. And whether biology finds what tips a lone body in a cave onto a 48-hour day. Until one of those lands, the clock Siffre's body kept in the dark is a fact without an explanation.

Eli: For further reading: Michel Siffre’s experiments.

Mara: Follow science with us—the open question is: what shapes our sense of time?

Eli: That's it for today. I'm Eli.

Mara: And I'm Mara. Thanks for listening, and until next time on Angle.