Why Does Time Slow Down and Speed Up?

Illustration: Elena Scotti (Photos: Shutterstock)
Giz AsksGiz AsksIn this Gizmodo series, we ask questions about everything from space to butts and get answers from a variety of experts.

Time contracts, expands, swallows and spits you out into this instant, which feels—depending on your perspective—either impossibly remote from where you were two years ago or barely removed from it at all. Flight delays, breakups, bouts of serious illness—all can bring you back to the high school classroom where it’s somehow slo-mo clock. You feel every tick. Meanwhile, an uneventful year can spool out in what feels like six days. Or maybe the reverse is true for you. The perception of time is intensely personal, not to mention effectively unmeasurable. But few if any internal clocks are synced to UTC—no one experiences time at an even, unvarying rate. For this week’s Giz Asks, we’ve reached out to a number of experts to find out why.


Aaron Sackett

Associate Professor, Marketing, University of St. Thomas, who research focuses on judgement and decision-making, among other things

One of the main reasons our perception of time fluctuates so much more than many other stimuli in the world around us is that we can’t detect time directly through our senses. Our eyes detect light, our noses and tongues detect physical matter, and so on. But there is no sensory system dedicated to detecting the passage of time. Instead, our brains have to figure it out indirectly, and that opens the door to many possible influences.

If you’re thinking about how time is currently passing by, the biggest factor influencing your time perception is attention. The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time’s passing—perhaps by something interesting happening nearby, or a good daydreaming session—you’re more likely to lose track of time, giving you the feeling that it’s slipping by more quickly than before. “Time flies when you’re having fun,” they say, but really, it’s more like “time flies when you’re thinking about other things.” That’s why time will also often fly by when you’re definitely not having fun—like when you’re having a heated argument or are terrified about an upcoming presentation.

If, on the other hand, you’re thinking about how time has passed since some past event, the biggest factor influencing your time perception is memory. Generally speaking, the more events you can remember happening in a span of time, the longer that span will feel. If you think back to an event from a year ago, the extent to which that feels like a short or long time ago is largely dependent on how much “stuff” your mind recalls between now and then. In isolation, a single event from last year might not seem so long ago. But if recalling that event leads you to reflect on many other events that happened since then (for example, perhaps you’re reminded that since then you’ve switched jobs, gotten a new apartment, started a new romantic relationship, and begun learning a new language), that event will feel considerably more distant as a result of this additional context.

A strange and interesting side-effect of all of this is that you can often feel like time has simultaneously dragged and flown by. At the end of a packed-full day—perhaps an eventful day of vacationing, or a busy day at work with lots of different activities—you may feel as though time has flown by, and yet… that very morning feels like days ago. Your mind hasn’t paid close attention to time all day, making the day feel brief and time’s passage quick. Yet you have memories of many events since the day started, making it feel like it has been a very long day indeed. I suspect that mixed signals from attention and memory are often the reason why we find our own perception of time so interesting.

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Philip Gable

Associate Professor of Psychology and Director of Experimental Psychology at the University of Alabama, whose research focuses on attentional scope, memory and time perception, among other things

Einstein observed that our experience of time is subjective. When descending the first hill of a rollercoaster, or being in a car careening out of control, time may seem to slow. Yet, time seems to “fly” when you are having fun! It is the emotional experience in each of these situations that makes time seem to go faster or slower. But, is emotion the only reason?

This is where motivation, or the impetus to act, comes into play. Usually, we want to approach pleasant things, like dessert, and avoid unpleasant things, like threats, but sometimes we want to approach negative things when we are angry, such as mean people. It is this motivational system to approach or move away that changes our perception of time. Motivation to approach causes time to seem to pass more quickly, whereas motivation to withdrawal causes time to seem to pass more slowly.

Functionally, time passing more quickly during approach motivation causes us to spend longer amounts of time acquire food, money, or even revenge. In contrast, time passing more slowly during withdrawal motivation causes us to get away from potentially harmful situations faster.

Simon Grondin

Professor, Psychology, Université Laval (Québec), and the author of The Perception of Time—Your Questions Answered

Time perception could be approached in so many ways, from the processing of milliseconds to the impression that life passes more or less faster over life span. Indeed, time determines most aspects of life, and the adaptation to the requirements of life requires being able to perceive time efficiently.

If you are listening to radio and there is a moment of silence, you will soon notice that something (speech) should happen, that something temporal, a slightly too long gap, happened. We are probably always ready to be involved in a timing activity to capture the temporal abnormalities. You may stop at the red light on your normal way, but will soon feel something is wrong if it takes just a slightly longer duration before it turns to green. No need to start timing when you arrive; it looks as if there is a system, an internal clock of some sort, that you can read at any moment to be informed, to let you know that it takes too long. And this impression that it takes too long could be magnified if you are in a hurry. It is as if this clock is sensitive to arousal, as if the clock turns faster with higher arousal. In psychology, researchers often posit that there is such a clock, namely a pacemaker emitting pulses, and the accumulation of these pulses determines the experience of time, the impression that a time interval is short or long. Any event having an effect on arousal, as is the case for instance with events provoking emotions like joy or fear, is susceptible to disturb time perception.

There are other situations where time seems to fly. The key ingredient of this impression is attention. If you pay attention to time, time won’t fly. But if you are busy doing a pleasant activity, you will not see time passing. This effect of attention on time perception is one the most repeated finding in the timing and time perception literature. If you have a cognitive task, not necessarily pleasant, that captures your attention during a given period of time, you will find this period to be short, shorter than if you would have had no activity during the same period. In other words, the accumulation the pulses referred to above is under the control of attentional mechanisms.

Time is also crucial, under one form or another, in different pathologies. It is known for instance that people with ADHD will have difficulty to wait and may even have some difficulty to read future consequences (kind of “temporal myopia”). The relation to time may also be distorted on a larger scale. Anxious people, more than others, will have the impression, that a given distance in the future is close, a tendency that goes in the opposite direction for depressed people who are inclined to be turned towards the past.

On an even large scale, we sometimes feel that time is now passing faster as we get older. Here, we are not dealing with “short or long”, but with “fast or slow”. The fact of being so busy at some period of life may lead to the impression that, at the end of a given week, not as much as planned or expected at the beginning of that week was done. The repetition of such impressions may lead to the impression that time passes faster than it used to, when there was less to do during childhood. Indeed, this is one of several hypotheses for explaining this impression that life is passing faster as we get older. This overall impression may also be related to the accumulation of occasions where we find ourselves so surprised that a given event occurred so long ago. When you are 8, nothing happened 10 years ago; but when you get older, you may have some vague impression that an event happened 8 or 10 years ago, while this event may have happened 20 years ago. “September 11” did not happened roughly 8 or 10 years ago; it happened 8 + 10 years ago.

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Adrian Bejan

Professor, Mechanical Engineering, Duke University, who has recently researched the question of why days seem shorter as we get older

Time’s flying by is of concern only to those getting older; the young don’t have this problem.

My work is physics, and the physics of this are very simple. Our eyes record images, but they are not recording images continuously; they’re taking the equivalent of snapshots. The process is staccato, jerky, like a horse-drawn buggy on a bumpy road. These discrete images travel from the retina to the brain, in a flow of electrical signals. That travel is facilitated by a link—the link between the retina and the brain—and it has a speed. With age, as the body grows, the length of those links, and the distance between the retina and the brain, increases; meanwhile, as one ages further, the speed of these signals decreases, as the body degrades. This degradation effects every muscle in the body, including the eyes—so in a sense our ‘camera’ gets rusty and starts to move slower, and the number of clicks decreases each day. This is why an aging person feels like life is rushing by.

But there are things you can do to change this process. One would be to experience more images worth clicking or recording with your eyes—by doing different things, avoiding routine, avoiding being an automaton. It pays to get off the couch. What’s important is to stop being boring, not only to yourself but those around you, and to experience new things. Another would be to take care of yourself physically—to preserve your body’s camera.

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Benjamin Devlin, S. Aryana Yousefzadeh, and Warren H. Meck

Department of Psychology and Neuroscience, Duke University

Voluntary and involuntary changes in our internal state have a strong influence on timing and time perception in the hundredths of milliseconds-to-hours range. Our internal state can be modulated by neurobiological, psychological, and environmental factors, and most often it is some combination of all three. Take the example of a hungry individual waiting for their food to come at a restaurant. The hungrier you are (which is causing changes in both your biology and psychology) the more likely it is going to FEEL like it is taking forever for your food to arrive. Conversely, if you are in a state of happiness and enjoying exciting conversations at the dinner table, then you are less likely to notice a 5-minute difference in the time it takes for the food to come.

A transient change in our internal state, like the emergence of fear, can affect our perception of time. Researchers have found that in situations of life-threatening danger, our brains adapt by releasing a surge of adrenaline, thus speeding up our internal clock and thereby making the external world appear to go slower. This could be one real-world example of an unconscious “slowing down” of time perception, thus potentially allowing us more time to make decisions and take effective action. The neurons in your brain that are responsible for time perception, typically referred to as “time cells”, are modulated by these various changes in our internal state. Together, these cells comprise timing circuits in the basal ganglia that are damaged or lost in some human neurodegenerative diseases (i.e., Huntington’s disease and Parkinson’s disease). Patients suffering from these diseases experience disruptions in their ability to accurately time durations in the seconds-to-minutes range. These deficits can be partially remedied with treatments that affect the release of the neurotransmitter dopamine from these cells, suggesting a direct neurobiological link between dopamine levels and time perception. Additionally, dopamine is a reward signal that affects our perception of time by speeding up and slowing down our internal clock based on how pleasurable our experiences are.

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It’s also the case that time perception and cognitive processes such as attention and memory are intrinsically linked. If we’re highly engaged in what we’re doing, for example, we probably aren’t paying very much attention to the passage of time unless temporal processing is an important part of the task. In this case we effectively lose track of the “ticks” and “tocks” generated by our internal clock. As a consequence, the engaged activity feels shorter (i.e., time flies) compared to when we’re constantly thinking about how much longer we have to wait until we can finish the task and move on (i.e., time drags). How an experience fits within a temporal context also determines the speed of our internal clock, which is why Fridays seem to pass a lot faster than Mondays. Working through a Monday in the context of “the beginning of a week” with a long to-do list makes us feel like the day (and the rest of the week) is never going to end. By the time we get to Friday, however, we feel like we have put the worst of it behind us and are motivated to get through the day and start the weekend.

Memory-related timing processes have recently been characterized in brain regions that are important for episodic memory – i.e., the hippocampus and entorhinal cortex. Some researchers have posited that time perception is largely a function of binding together the temporal sequence of events. If more information is stored in a shorter timeframe within episodic memory, this can be interpreted as a slower perception of time. In short, a variety of physiological, pharmacological, and cognitive factors influence the way we perceive time in the hundredths of milliseconds-to-hours range, and these factors are constantly and dynamically changing both within and outside of our control.

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