Aging is defined by time. Even though our bodies are in a constant process of change, some cells in our bodies remain with us from conception. Our bodies have 37 trillion cells that are constantly duplicating, updating, maintaining and replacing themselves. Each cell contributes to a specific organ in the body. Jonas Frisen, a stem cell biologist at the Karolinska Institute in Stockholm developed a method for determining the age of each organ. Although some cells remain with us the duration of our life - neurons of the cerebral cortex, cells of your inner lens in our eyes, muscle and valve cells of your heart - the rest of our body is in a constant frenzy of change and rejuvenation so that with time we get to replace whole organs:

  • Intestines replaced every 2-3 days old,
  • Taste buds replenish themselves every ten days.
  • Skin and lungs (2-4 weeks)
  • Liver is replaced (5 months)
  • Nails (6-10 months).
  • Red Blood cells, every four months after traveling over 300 miles and going through the heart 170,000 times, 60 times per hour our red blood cells are given respite and are renewed
  • Hair if the follicles have not fallen off every 3-6 years)
  • Bones (every 10 years) and lastly
  • Heart--most of it (every 20 years)

Despite this newness, we measure our age by our chronology - how much measured time has elapsed. On average our body is only eleven years old. However with each replication a slight imperfection results. We see these imperfections and assign it to the “aging” of our bodies. We resign ourselves to accepting our aging as an indication of our chronological time but it isn’t. Physical aging are mistakes that happen. But we mesh the two together. Aging and time are glued together and only when we look closer do we see that each is unique and separate.

We have a story, a narrative arc playing in the background of our life. Time is a special dimension, an unrelenting linear and absolute progression. Although time seems intuitive, we have great difficulty even conceptualizing what time is, let alone explaining what it is.

A quick dive into quantum physics dispel any such illusion that time is stable or linear. For example in quantum entanglement two electrons remain connected, no matter how far apart they are, in time synchrony. The electrons remain attached in time but not space. In this quantum universe, time doesn't exist at all. In the split slit experiment - where electrons interfere with each other after going through two slits but only when they are not being recorded - seems to suggest that electrons can go back in time, or at best do not conform to our linear time. Whatever our linear time means. Einstein called time a “stubbornly persistent illusion”. He was wrong, time is our reality that fails to find evidence outside of our consciousness.

Time is something that we create for ourselves and we do this by measuring it. And we measure time with great relish. Other than external means of measuring time - an impressive and historical array of clocks and watches, celestial movement, temples and seasonal rituals - our mental representation of time is fundamentally linked to our body. Our internal time is determined by our own biological, neurological and emotional reality. Many theories attempt to explain how time emanates from our mind and our body. But the biggest contributor to our sense of time is our own sense of aging - time speeds up with age.

Internal Clock

Our bodies are sophisticated watches - chronographs - that seem to get faster with age. The psychologist William James at the turn of the 20th century observed that years seems to pass more rapidly as we grow older. Many have attempted to prove this observation, but with variable success.  Then the French biophysicist Lecomte du Nouy in 1937 associated this phenomenon of a racing time with the slowing in cellular activity in aging bodies. He connected time with our physiological processes. To this day, although there is much evidence supporting this theory, the relationship between our physiological processes and our estimate of time remains contested. Studies do not show clear-cut outcomes. We have not found all of the mechanisms that control our sense of time. But in our explorations, we are learning more about the variability of how we judge time.

For example in 1958 Sanford Goldstone, William Boardman and William Lhamon with Baylor University Houston, Texas asked institutional older adults to count 30 seconds at a rate of one count per second. Older adults (average age 69 years) tended to report a shorter time interval then younger adults (average age 24 years). But the evidence goes back and forth. In 2005 Marc Wittman and Sandra Lehnhoff with the Ludwig-Maximilian University Munich, agree that despite the widespread belief that the subjective speed of the passage of time increases with age, results are inconsistent. They support the widespread belief that the passage of time speeds up with age although they do point out that such incremental changes are subtle.  Despite stereotypes that even though older people see the passage of time increasing, younger participants anticipated that time will be slower when they get older. The authors also concede that there remain other factors that conflict with a purely age-based interpretation of the speeding of time.

Older adults switch from "time lived since birth" to "time left to death.” One lag (since birth) seems long while the other lag (left to death) seems short and is getting shorter. Perhaps it is this sense of urgency, and our attempt to catch up with our legacy when we see time as going too fast. In an experiment in 1961 Michael Wallach, and Leonard Green with MIT found that both the type and quality of activity and the perceived time remaining makes time speed up. This sense of urgency is what influences our impression of time accelerating. Our activity and our sense of urgency determine time. Those older adults who are dying and fearing death feel more pressured by the passage of time. Similarly those who are busy also see time passing by faster. In contrast, Steve Baum with Sunnybrook Medical Center, Toronto and his colleagues report that time also moved slower for many institutionalized elders.  People in institutions who engage in few daily activities see time as going by more slowly. Older adults report both extremes; time getting faster while others report time going slower.


This does not make sense. And we are missing the first principle of gerontology - heteroscedasticity. Older adults become more varied the older the group becomes.

We have older adults who are catatonic in nursing homes while others remain in the community, active, engaged and at the peak of their capacity.  Jacob Tuckman uncovered this fact in 1965 when he reported that although there is a slight increase in the cadence of time among older adults (60 and over) he reported that they were both the group that saw time pass quickly as well as the group that saw time most slowly.  Older adults were just more aware of time and reacted to the perception of time in “both directions.”

And we know that time is flexible and malleable in our mind. The elaboration came when Richard Block replicated a study that found that time intervals with many events are experienced as longer than intervals filled with fewer events.  In uneventful situations, such as in a typical nursing home when a period of time is not filled with distracting events, time seems to pass slower.  For those adults that are engaged and active, there is not enough time to complete their activities, and therefore time goes by too fast. We might be measuring time on the basis of events that happen. Our physiology not only dictates time, but we look at the environment to tell us how fast or slow we need to move time.  The environment might provide a metronome. We are looking for events that happen in order to synchronize our internal time clocks. This is known as the Kappa Effect.

We intuitively measure time by the space in between events - in this case, blinking lights. The experiment is easy. Imagine you have a reference light that blinks once for a split second, then spaced a few inches to the right another light blinks and then twice as far to the right another light blinks. Even though the time lag between the second blink and the third blink is the same, we always assume that the third blink is delayed because it is further away from the first blink. Our internal clock is sensitive to how objects appear in space.  Events bunched together are seen as occupying a shorter period of time while events that are spread out are seen as taking longer time. But it is not just distance. There are numerous factors that influence our timing.

Some of these factors include the type of stimuli (visual, auditory, tactile), the intensity, size or strength of stimuli, complexity, uniqueness, including background and contrast, as well as speed and variance in speed all influence whether we perceive time as slowing or speeding. Most importantly, we attach emotional meaning to events. In 2007 Sylvie Droit-Volet  and Warren Meck reported how our sense of time is moderated by how we feel. So that time seems short when we are having fun and extends when we are bored.

It could be that time does not get faster with age but it seems that it does because we have an urgency to do things before we die. We speed up time in order for us to coherently make sense of our urgency. We tend to try and accomplish too many things despite perhaps not having the energy to accomplish them. And it is not our perception that slows down or speeds up but our memory of it.

Similar to the experience of fear, where time seems to slow down, what speeds up n is our memory not our attention. David Eagleman with Baylor College of Medicine, Houston, Texas designed a clever experiment that conclusively showed that fear for example does not actually increase how fast we are at noticing events, and therefore slowing time. He found that instead what happens is that we gain improved memory that packs that time unit with many details and events.  Knowing this however does not explain neurological conditions that results in both time speeding as in the “zeitraffer” phenomenon, or the obverse experiences called “akinetopsia”, when motion slows or stops altogether.

The fact that time perception can reflect neurological problems indicate that something “mechanical” is happening in the brain. It seems that motion and time are related neurologically. This is not only how we think or memorize, it is how we are built. The only other place this happens is in cinema: a movie that is controlled by the timing of projecting individual frames. Likewise, our brain records individual frames - many more than we are aware of, and perhaps with many different layers, emotional, visual, auditory - and then like a film reel plays them out for us on the basis of an internal time. The brain plays these memory frames at speeds that make the story coherent. So if more detail is needed then it slows the film down (fast time) and when the story is uneventful the brain speeds it up (slow time). All of this is done in the visual cortex.

We are learning that time is a complex psychological phenomenon. It is not an illusion, but a reality that exists at the center of our consciousness. With time there are variances in the context (busy vs bored), differences in individual experiences (older vs younger) and there are also complexity of time (neurological vs external measures.) Understanding that we have memories that are snapshots (some of which remain in our subconscious) rather than a movie, elevates time to the master conductor of our memories. Time orchestrates our memories. But this still does not explain why older adults are more prone to speed time up.

The Logarithmic Time

Aging is like a logarithm, the older we get the short the percentage of time that has elapsed. It’s just mathematics. This was first estimated by Paul Janet (1823-1899). He found that the apparent length of an interval at a given time is proportional to the age of the observer. For a ten-year-old a year adds 10% to her life, but only half that value (5%) for a twenty-year-old. For a 90 year old, 10 years is an ninth of their life, while for a twenty year old 10 years is half their life., hence the perceived shortness of time as we get older. James Kenney wrote an interesting blog on this function and he estimated that time is perceived logarithmic, meaning that it gets shorter as we age. He referred to this function as Logtime. In estimating the length of a year we compare it to our age. We see time proportionally so that the older we are chronologically the smaller the proportion of a time unit. We are predisposed to see time going faster, regardless of all other factors. This observation is further supported by an earlier understanding of time by a German physician Karl von Vierordt (1868). Vierordt‘s Law states that short event are perceived as longer than they are and longer events as shorter.  There is a convergence.  This also applies to historical events as well where we estimate long past events as more recent than they were which gives the impression that time is speeding. For older adults, events that happened thirty years seem more recent. And we do this to help our memory.

Between two to five seconds seem to be the time where we are present, and within this short period we have a fairly accurate time. While memory and anticipation form the majority of our awareness. It helps therefore to have a retrievable memory that assigns more importance to the more recent events (and therefore more likely to be pertinent) and to bunch experiences into more manageable time limits.


Again, Steve Baum and his colleagues report that among 296 institutionalized and community dwelling elderly (average age 75.4 years) faster time perceptions were associated with being healthier - less clinical depression, enhanced sense of purpose and control, and “younger” perceived age - while the opposite perception held true for older adults who were more frail and saw themselves as “older” where time was going slower.

If time orchestrates our memory, dictating the speed and therefore the length of our life’s story then it determines or at least indicates our expected life span. Logtime determines that this period of perceived remaining time is experienced to be shorter the older we get. That is the mathematics of the basis of our perceived shortening time. If our Logtime is determined by how much time we believe we have remaining, then the healthier we are the more accomplishments we want to achieve and the faster time seems to pass. The more things that we want to accomplish, the greater the urgency and therefore the shorter we feel our remaining time to be. Time is faster. 

We dictate time speed by our urgency and our age. In return, our time metronome selects memories to make the story, our narrative arc, coherent. The counter-intuitive prediction being that the faster you think that time is going, the longer you are likely to live. How we see time is an indication of our life story. We might be accessing cues from both our body and the environment that tells us when that final curtain is likely to be.

Mario D. Garrett