In 1890, William James finished a book he had been working on for twelve years. He had started it when he was thirty-six. He finished it at forty-eight. The book was “The Principles of Psychology,” two volumes and more than twelve hundred pages, and somewhere inside it he described an observation about time that a French philosopher named Paul Janet had made roughly a decade earlier.
“The same space of time seems shorter as we grow older,” James wrote, citing Janet’s idea. “In youth we may have an absolutely new experience, subjective or objective, every hour of the day.” (Source)
That was written in 1890 and it’s still the most honest statement of the problem anyone has produced. Not the solution. The problem. Stated with the precision of a man who had just watched twelve years collapse into what felt, looking back, like a couple of long afternoons.
I turned sixty this September. My father used to say that by his fifties, summers went by so fast he barely had time to resent them. Gerald Holt wasn’t a philosophical man in any conventional sense, but he noticed things. He noticed that time had changed velocity sometime in his forties and never slowed back down, and he wanted to know why. I’ve been asking the same question, somewhat more systematically, for most of the past decade.
Here is what the research actually says. And what it doesn’t say, which matters more than people realize.
The intuitive explanation is the one Janet formulated and James repeated: the proportional theory. At age ten, a single year is roughly ten percent of your entire life. You have never seen one like it. Every fall is a first fall at a new grade, or the year you got a bicycle, or the summer your grandmother died and everything changed. At sixty, one year is less than two percent of your accumulated experience. The year doesn’t feel shorter because time is literally moving faster. It feels shorter because it is, proportionally, a smaller piece of the whole.
This is a satisfying explanation and almost certainly incomplete.
The proportional theory predicts that time should accelerate smoothly and continuously across a life: a linear ramp from the slow childhood summers to the compressed decades of old age. That isn’t what people actually report. What people describe is something more episodic. Certain periods feel long, the years of new jobs and young children and first apartments. Other stretches vanish: the ones defined by settled routine. If proportion were the only mechanism, you wouldn’t expect that texture. Something else is doing the real work.
The more useful explanation has to do with how the brain constructs memory, and through memory, its sense of time passing.
The brain doesn’t experience time the way a clock measures it. It experiences time through the density of memories it lays down. A week in which you started a new job, moved to a new city, and met someone you would end up knowing for the rest of your life registers as a very long week. Not because the days had more hours. Because each day contained more distinct episodes for the brain to file and process. Each genuinely new experience requires the construction of a new memory trace, and those traces are what give elapsed time its felt weight.
Now consider what happens when life settles. You wake at the same hour. You drive the same route. You eat lunch at roughly the same time. The brain, confronting a scene it has processed hundreds of times, doesn’t build a new memory. It retrieves the template it already has. The day is handled efficiently. And efficiently, from the brain’s perspective, means quickly. A day that required no new encoding leaves almost no record, and a thin record feels, in retrospect, like no time at all.
Claudia Hammond, a psychologist who has written extensively on how we experience time, calls this the “holiday paradox.” You take two weeks somewhere unfamiliar. In the moment, the days seem to whiz by: there’s too much to notice, too much that doesn’t fit your existing templates. But when you return home and someone asks how the trip was, it feels like a rich two weeks. A long two weeks. The two weeks at your desk before the vacation barely registers. You couldn’t reconstruct what happened on that Thursday.
The paradox is that the stretches that feel fast in the moment feel long in memory, and the ones that drag while they’re happening leave almost nothing behind. (Source)
I want to stop here and acknowledge something the research community has been honest about, even if the popular writing on this topic often isn’t.
A 2005 study by psychologists Marc Wittmann and Sandra Lenhoff surveyed 499 people between the ages of 14 and 94 and found that age accounts for at most about ten percent of the variation in how fast people feel time passes. Ten percent. The rest of the variation, roughly ninety percent, is individual, not age-driven. Some sixty-year-olds experience time as moving quickly. Some thirty-year-olds describe the same thing. The relationship between aging and time acceleration is real but modest, and it explains far less of the individual experience than the way people talk about it would suggest. (Source)
This is worth knowing before you conclude that everything inevitable is happening to you on schedule. It might be. It also might be something else entirely.
There is a second mechanism that operates at a more neurological level, and it’s less settled than the memory-encoding account.
The brain maintains an internal sense of duration through circuits that appear to depend on dopamine, the neurotransmitter most associated with novelty and reward. The working hypothesis, supported by animal studies and some human research, is that dopamine helps calibrate the internal clock: high-dopamine states make intervals feel longer, low-dopamine states compress them. If this is right, the natural decline in dopamine production that comes with age would make each moment feel shorter, not in retrospect but as it’s happening.
A 2016 study of 233 healthy adults found that people over fifty tended to underestimate the length of a two-minute interval compared to people under thirty, which is consistent with the hypothesis. (Source) But whether day-to-day subjective experience is meaningfully changed by this, whether it explains the felt acceleration rather than just explaining a particular lab task, is genuinely uncertain. The evidence is suggestive, not conclusive.
I wrote earlier this year about what actually changes in the brain after sixty, and what actually improves. (Source) The dopamine research belongs in that same category of things that are real, not fully understood, and more conditional than the headlines make them sound.
Which brings me to what the memory-encoding research does say, without overpromising.
The research consistently shows that novelty is the primary driver of felt duration in memory. Not effort, not pleasure: novelty. A difficult week doing the same difficult thing you’ve been doing for twenty years will feel short. A week spent learning something you’ve never done, even if the learning is frustrating, tends to feel long in retrospect. The brain is measuring elapsed time by the rate at which it had to process new information, and new information is the signal that something worth remembering happened.
What this doesn’t suggest is that you should fill your schedule with experiences. That produces the same compressed memory that routine does, just with different tasks. A year in which you were very busy doing the same kinds of busy things is a year that will feel, in retrospect, as thin as a quiet year. Busyness and novelty aren’t the same thing, and confusing them is a very common error.
Something closer to the actual implication: notice things you haven’t noticed before, in places you’ve already been. Drive a different route home. Look at the corner you’ve driven past eight hundred times and actually look at it. Take up something that requires your brain to build new templates rather than retrieve old ones. Not because a study tells you to, but because the mechanism the research describes is pointing at something specific: the brain marks time by marking newness, and you can feed it newness without going anywhere.
One honest caveat from the research: a 2022 study found that the memory boost from novel environments was measurable in younger adults but was absent in older ones. (Source) The relationship between novelty and felt time gets more complicated with age, not simpler. The prescription is real but it doesn’t resolve cleanly.
My father’s summers were going by fast because he had spent thirty years learning exactly how to live them. He’d seen them. They weren’t taking him anywhere new. I don’t think he knew that was the problem. He just noticed that time had changed and wanted to know why, which is more than most people get around to asking.
He died before I was far enough into my own fifties to understand what he was asking about.
What the research can offer, with appropriate caution: the brain marks time through the residue of new experience. Routine is efficient. Efficiency is the enemy of felt duration. The years feel shorter when there’s less for the brain to encode, and you have more control over the rate of encoding than the proportional theory, with its inescapable arithmetic, would have you believe.
What you do with that is yours to figure out. The research ran out here.
