LIFE | TIME PERCEPTION

Why Do Days Get Shorter As We Get Older?

And we even count the seconds differently!

Recently, I decided to read an old diary of mine from when I was 16. Reading it, I couldn’t help feeling that my days were longer back then, that I had a lot of time. Now, it seems that the clock runs faster, that I’m always out of time. One day is Monday, and I have the whole week ahead; the next day is Sunday, and I haven’t even got some rest!

Obviously, the flow of time does not change. What changes is how we perceive it. This is a feature of how our brain works. An illusion.

And the key to understanding this illusion is understanding the concept of perception.

Photo by Jeremy Thomas on Unsplash

How do we perceive the flow of time?

We can only perceive sensory stimuli. That is, what we detect using our five senses — smell, touch, taste, hearing, and vision. And these stimuli can be measured. For example, we can measure how loud a sound must be for us to hear it or how much sugar a lemonade needs to be tasty.

But when it comes to measuring the perception of time, things are different. First, we do not have one specific sense to detect changes in time. Second, we cannot manipulate the speed of time, so we cannot directly measure how changes in time flow affect us.

But we can still indirectly assess the perception of time by testing how different people perceive the same time length.

In one study, the researchers asked the participants to mentally count 120 seconds (2 minutes) with their eyes closed. They registered how long it took each participant to finish using a chronometer. Here’s what they found:

On average, counting 120s took:

• the younger participants (15 to 29 years old) — 115s
• the young adults (30 to 49 years old) — 96s
• the older adults (50 to 89 years old) — 87s

This simple experiment shows that older individuals counted 120s faster than the younger, confirming that the perception of time accelerates as we get older.

Why does this happen?

While we do not possess a specific sensory system for sensing time, we perceive the flow of time through our regular experiences in an ever-changing world. For example, we know that time passes as we see days turning into nights or the changing of seasons. We feel changes in our bodies and changes in our lives.

So, it has to do with our life experiences and how those experiences mark our memories.

All seconds are equal, but some seconds . . .

We do not remember all the moments in our lives equally. There are events that we recall more vividly, with more details. Such events stand out. They are landmarks, time references, identity makers. The pillars of our biographical memory.

No doubt, we tend to remember more details from our youth experiences. Especially, first times — first kiss, first sexual relationship, the first time we visit a new town, first time traveling to a foreign country, first experience living alone, first job…

Novelty is key. New experiences leave deeper marks on our lives and thus on our memories. The thing is, the probability of living new, defining experiences is greater during the first decades of our lives.

Imagine your life is like a bag full of small boxes. An event occurs every time a ball falls inside a box. But a new event only happens when a ball falls inside an empty box; the other balls in that box are repeated events. You only have so many boxes. So, the probability of a ball falling inside an empty box will decrease over the course of your life, as you are running out of empty boxes.

If novelty is what makes us aware of time landmarks, then our perception of time can only get weaker as we age.

It is like a logarithmic curve:

As we get older and collect experiences, only the meaningful ones will leave a mark on our perception of time. Image by the author.

Moments as a collection of mind pictures

We remember through images. When we think about an event in our life, we see it in our minds. But the way we collect these pictures changes through time.

It has to do with physics. We capture images through saccades, the rapid eye movements when we change our sight. The images then travel from our eyes to our brain, where they are analyzed and may be stored.

Babies don’t do much, but they are incessantly looking at everything, capturing new images of the world around them. Children have faster eye movements than adults, and the images travel a shorter distance from the eyes to the brain.

As we grow up, the distance from the eye to the brain gets longer and more complex. And as we get older, our movements get slower, including saccades and mental processing. We get fewer images, especially new ones.

As a result, the frequency of mental images is greater during our youth.

The misalignment between perceived time and real time during lifetime, modified from Bejan (2019).

This figure highlights another feature of time perception throughout life:

The time we lived is different from the time we remember

When we are having a great time — for example, those vacations in which we have a lot of fun — time seems to fly. But when we look back, we remember those vacations so dearly and with so many details that we perceive them as long. It’s the ‘Holiday Paradox’.

We memorize our dearest experiences differently — they occupy a special place in our memories. They mark us, and their meaning changes naturally with time.

So, going back to my diary…

I had started writing because there was something new in my life: for the first time, I had a dog. Those pages register the first year in his life and my experiences in that new relationship.

There, I found a lot of episodes I remembered so well from my youth! Those were distinctive experiences. I have the images carved in my mind, and I have talked about those episodes so often that they will stay with me forever.

Those images, those feelings, those discoveries… I will never forget!

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