We tend to talk about time as though there’s one clean scale running underneath everything, with seconds and years acting like neutral containers that every process simply fills at its own pace. That works fine for ordinary life, where a clock gives us a shared reference and there’s no real need to ask what a second means to the thing being measured, but once you start comparing systems that change on radically different timescales, that shared reference begins to look more useful than fundamental.
A nervous system can go through an enormous amount of activity in a fraction of a second, while a geological process may barely register any visible change over the course of a human lifetime. The same amount of clock time can contain very different amounts of meaningful change depending on the system, which suggests that our everyday sense of “fast” and “slow” is tied much more closely to the kinds of processes we’re used to experiencing than we usually admit.
That got me wondering whether time is really best understood as something that simply passes at a fixed background rate, or whether part of what we mean by time comes from the rhythms and changes happening inside the systems we’re looking at.
Time and Change
Aristotle thought time was deeply connected to change. In Physics, he described time in relation to motion and to the ordering of events into before and after, which already moves us away from the picture of time as some invisible substance flowing independently of everything else.
The connection becomes easier to see once you think about how clocks actually work. A clock always relies on some physical process that changes in a repeatable way. Pendulum clocks use oscillation, quartz clocks use vibrations in a crystal, and atomic clocks count transitions in atoms with extraordinary precision. We don’t somehow measure time directly; we compare one process against another process that we’ve chosen as a standard.
That raises a strange question about what time would even mean in a universe where absolutely nothing changed. If no physical process occurred and nothing could be compared with anything else, saying that an hour had passed would be difficult to connect to any observable difference in the world. You could still imagine time existing abstractly, but there would be no event that could mark its passage.
Aristotle didn’t collapse time into change completely, yet his view makes the relationship hard to ignore. Once time is tied to change, the pace at which different systems transform starts to become philosophically interesting rather than merely practical.
Different Systems Have Their Own Rhythms
Biology makes this especially obvious because living systems don’t operate according to a single internal tempo.
Circadian rhythms coordinate sleep, hormone release, body temperature, and other recurring processes over the course of roughly twenty-four hours, while different tissues also contain their own clocks that respond to signals from the environment and from the rest of the body. These rhythms are constantly being adjusted, synchronized, and sometimes thrown off, which is why things like jet lag can leave your body feeling out of sync even when the clock on the wall is perfectly clear about what time it is.
What I find interesting here is that biological time is already organized around change rather than around the abstract passage of seconds. A living system responds to recurring patterns, builds cycles around them, and develops its own internal schedule for when certain processes should happen.
That internal rhythm becomes even more noticeable when you compare organisms with very different rates of metabolism, growth, or aging. The same external interval can represent a large fraction of one organism’s life and almost nothing in another’s. A week doesn’t carry the same biological weight for every system simply because the clock gives it the same number of hours.
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| Circadian rhythms organize biological activity around recurring changes in light and darkness, giving living systems an internal way of tracking recurring cycles over time. “Overview of biological circadian clock in humans,” YassineMrabet, November 4 2007, Wikimedia Commons, https://commons.wikimedia.org/wiki/File%3ABiological_clock_human.svg. |
What Does “Fast” Even Mean?
The words “fast” and “slow” seem straightforward until you try to use them across very different scales.
A process unfolding over ten thousand years sounds almost impossibly slow from a human perspective, yet that judgment comes from comparing it with the pace of our own lives. For a system whose major changes naturally occur over geological timescales, ten thousand years may be a relatively short interval.
Science deals with this by changing the scale of observation until the process becomes visible. A researcher studying neural activity might care about milliseconds because meaningful changes occur within that window, while a geologist may need to think across millions of years before the pattern becomes clear. Neither timescale is more real than the other. Each one is useful because it matches the characteristic rate of the system being studied.
That idea starts to push against the instinct to treat human experience as the default scale for time. We call something slow because it changes too gradually for us to notice directly, and we call something fast when its changes blur together before we can consciously follow them, but those descriptions reveal as much about us as they do about the systems themselves.
Lived Time
Henri Bergson approached time from a very different direction because he was interested in how duration is actually experienced.
His idea of durée, usually translated as duration, challenged the idea that lived time can be fully captured by dividing it into equal units. A clock treats every minute as interchangeable, yet anyone who has been stuck waiting for something knows that experience doesn’t cooperate with that neatness. Ten minutes can feel drawn out in one context and disappear almost immediately in another, even though the measured interval hasn’t changed.
Memory seems to distort things further. Periods filled with unfamiliar experiences can feel longer in retrospect because more of them stand out as distinct, while repetitive stretches often collapse together when we look back on them. The amount of recorded clock time stays fixed, but the internal structure of the experience can be much richer or much thinner.
Bergson’s point was that scientific time and lived duration answer different kinds of questions. Science needs uniform units because measurement depends on them, but experience isn’t organized into identical blocks in the same way. The flow of time from inside a mind is continuous, uneven, and heavily shaped by attention and memory.
That distinction opens up an interesting possibility: perhaps asking how fast time passes can mean very different things depending on whether we’re talking about measurement, biological change, or conscious experience.
Physics Doesn’t Give Us One Universal Clock
Relativity pushes the question into physics itself.
Before Einstein, it was natural to imagine that the universe had one universal time running everywhere in the background, even if different observers happened to measure events differently. Special relativity removed that assumption by showing that observers in relative motion can disagree about elapsed time in a way that can’t be reduced to a simple measurement mistake.
General relativity goes further because gravity also affects how clocks run. Two clocks placed in different gravitational conditions won’t accumulate time at exactly the same rate, and this has been measured with modern atomic clocks. Satellite systems such as GPS have to account for these effects because the clocks in orbit don’t stay perfectly synchronized with clocks on Earth if relativity is ignored.
This gives us a much stronger sense in which time can differ between systems. The difference here isn’t about perception or biological rhythm. It’s built into the geometry of spacetime itself, where the amount of proper time that accumulates depends on the path an object takes.
The old picture of a single cosmic clock becomes difficult to hold onto once physics allows different observers to accumulate genuinely different amounts of elapsed time.
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| Relativity predicts that elapsed time changes with motion and gravity. This graph shows how those effects vary with orbital height, where clocks can accumulate time at slightly different rates depending on their position and motion. “Time Dilation vs Orbital Height,” Prokaryotic Caspase Homolog, February 10 2019, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Time_Dilation_vs_Orbital_Height.png. |
So What Kind of Time Are We Talking About?
By this point, I don’t think all of these examples should be forced into one definition.
Biological rhythms describe how living systems organize recurring change. Bergson was concerned with how duration is experienced from the inside. Relativity describes measurable differences in elapsed physical time. They’re connected by the broader idea of change, but each one is answering a different question.
That’s probably why conversations about time become confusing so quickly. We use the same word for several related ideas and then expect them to line up perfectly.
The more interesting possibility is that time doesn’t come with one obviously privileged scale. Different systems reveal different kinds of temporal structure depending on what they’re doing, how quickly they change, and what kind of measurement we’re using to describe them.
From that perspective, a clock gives us an extremely useful standard, but it doesn’t automatically settle every question we can ask about time.
So when we ask whether time is passing quickly or slowly, the question may be missing a reference point.
Quickly or slowly for what?
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